The stinger is 18mm rather than the calculated 14.5mm I may try sleeving that eventually.
Here are some photos:
Acceleration is the best that it has been.
Sunday, August 15, 2010
Zen is Zen
My new expansion chamber seems to be working better than my old one. It has a very smooth diffusion cone that expands to about a 90mm ID. my last one was 76mm and my first one was 70mm.
The stinger is 18mm rather than the calculated 14.5mm I may try sleeving that eventually.
Here are some photos:
Acceleration is the best that it has been.
The stinger is 18mm rather than the calculated 14.5mm I may try sleeving that eventually.
Here are some photos:
Acceleration is the best that it has been.
Monday, August 9, 2010
Sunday, August 8, 2010
I worked on tuning my Zuma. I have the head pipe a slip fit and it allows about 2" of movement. I first slid the pipe out. It really made the acceleration better. The top speed was one mph less. I moved the pipe in an inch from where I started with it. The machine really too a hit on acceleration and the top speed went up .6 mph to 48.6.
Perhaps I could lighten the rollers a bit and get the acceleration back. I had calculated that one inch is about a 4oo rpm peak change.
I am going to reassess my pipe design. My convergent cone is an average of 28 degrees. To my understanding a steep convergent cone will produce a strong reflection but over a narrow rpm range particularly in the rpm above the peak power rpm. It may also lead to increased temperature of the piston. I have not had problems with that issue.
I have decided to make a new convergent cone. I am designing for 18 degrees. Most formulas suggest between 14 and 20 degrees with the higher value for higher peaks.
Hopefully the engine will have a the ability stay in the powerband during the variator phase of running and then pull past the peak for top speed.
Perhaps I could lighten the rollers a bit and get the acceleration back. I had calculated that one inch is about a 4oo rpm peak change.
I am going to reassess my pipe design. My convergent cone is an average of 28 degrees. To my understanding a steep convergent cone will produce a strong reflection but over a narrow rpm range particularly in the rpm above the peak power rpm. It may also lead to increased temperature of the piston. I have not had problems with that issue.
I have decided to make a new convergent cone. I am designing for 18 degrees. Most formulas suggest between 14 and 20 degrees with the higher value for higher peaks.
Hopefully the engine will have a the ability stay in the powerband during the variator phase of running and then pull past the peak for top speed.
Friday, August 6, 2010
August 5, 2010
Got a chance to work on my Zuma today.
I put im a new contra spring. a blue polini spring. I have two alternative choices, a white spring was 3.74 mm x6 turns and the blue was 3.84x6 turns. I miked the stock spring. It was 3.99 x 4 turns.
The ID of the springs are 44.5 mm and the free length is 68mm for stock and 110mm for the aftermarket springs. I didn't measure the compressed length but would estimate it at 55 mm.
I am not versed on spring constants. I think it would be safe to say that the stock spring has more force but less preload.
I put in the blue spring as it was thicker than the white.
The bike runs better, I am still running the 4gram x6 weights and the bike picks up faster at low end and doesnt flatten out at 30+ mph (before pulling to 50) like it did before. I would say that at low rpm it had more force keeping the rpm higher. I didn't get nearly as much rpm drop off at higher rpm at around 30 mph.
It is irritating to see the speedometer go to the peg and hear the rpm continue to grow.
My compression is pretty low as my cylinder was raised and the head was not machined equally yet. My squish is entirely too fat.
Got a chance to work on my Zuma today.
I put im a new contra spring. a blue polini spring. I have two alternative choices, a white spring was 3.74 mm x6 turns and the blue was 3.84x6 turns. I miked the stock spring. It was 3.99 x 4 turns.
The ID of the springs are 44.5 mm and the free length is 68mm for stock and 110mm for the aftermarket springs. I didn't measure the compressed length but would estimate it at 55 mm.
I am not versed on spring constants. I think it would be safe to say that the stock spring has more force but less preload.
I put in the blue spring as it was thicker than the white.
The bike runs better, I am still running the 4gram x6 weights and the bike picks up faster at low end and doesnt flatten out at 30+ mph (before pulling to 50) like it did before. I would say that at low rpm it had more force keeping the rpm higher. I didn't get nearly as much rpm drop off at higher rpm at around 30 mph.
It is irritating to see the speedometer go to the peg and hear the rpm continue to grow.
My compression is pretty low as my cylinder was raised and the head was not machined equally yet. My squish is entirely too fat.
July 12, 2010
Too hot to ride today so I decided to take my zuma motor apart. I remeasured my ports and decided to open them up a bit. I looked at the port tunnels on the cylinder and realized that I would not meet my goals with carving. The exhaust port is already at 60% width and I have not done much to make it wider. When I got done with my files the exhaust port is now about 24.6 mm from the top of the cylinder. It is about a mm above what I was running prior. I used my files and worked for several hours on smoothing the ports. I could reach all the way into the transfers. My transfers went up half a mm to 32.5. The left side was .5 mm lower than the right. I did my best to equalize.
The problem that I am encountering is that the tops of the port tunnels are very close to the stock port figures. I decided that I would add a second base gasket to increase mean port timing and remove material from the top. My stock squish was 1.4 mm. I removed some material from the cylinder head. I didn't get enough removed and my squish is now 1.7 but better too much as I can cut off more. I am going to take it to about .8mm.
I have been running 24 grams on the stock variator. Too much right now, the bike is a dog until 33-35 mph then rockets past the speedometer stop. I didn't use my GPS as I figure I need more static compression. I may need to go back to my 19.5 (total) gram set of weights. I am hoping that getting the compression back up will do a lot for mid range. That is my next step.
Too hot to ride today so I decided to take my zuma motor apart. I remeasured my ports and decided to open them up a bit. I looked at the port tunnels on the cylinder and realized that I would not meet my goals with carving. The exhaust port is already at 60% width and I have not done much to make it wider. When I got done with my files the exhaust port is now about 24.6 mm from the top of the cylinder. It is about a mm above what I was running prior. I used my files and worked for several hours on smoothing the ports. I could reach all the way into the transfers. My transfers went up half a mm to 32.5. The left side was .5 mm lower than the right. I did my best to equalize.
The problem that I am encountering is that the tops of the port tunnels are very close to the stock port figures. I decided that I would add a second base gasket to increase mean port timing and remove material from the top. My stock squish was 1.4 mm. I removed some material from the cylinder head. I didn't get enough removed and my squish is now 1.7 but better too much as I can cut off more. I am going to take it to about .8mm.
I have been running 24 grams on the stock variator. Too much right now, the bike is a dog until 33-35 mph then rockets past the speedometer stop. I didn't use my GPS as I figure I need more static compression. I may need to go back to my 19.5 (total) gram set of weights. I am hoping that getting the compression back up will do a lot for mid range. That is my next step.
MacGyvering my Zuma
July 10, 2010
I measured my squish band yesterday it was 1.35 mm. I used the rosin core solder method. I checked several times and only once did I get that low of an amount. Several other readings were in 1.7mm range. The stock head has a rather strange shape of the squish area.
Next time engine is apart I am going to check the jetting by the oil line method and perhaps reduce the squish along with some more porting.
I measured my squish band yesterday it was 1.35 mm. I used the rosin core solder method. I checked several times and only once did I get that low of an amount. Several other readings were in 1.7mm range. The stock head has a rather strange shape of the squish area.
Next time engine is apart I am going to check the jetting by the oil line method and perhaps reduce the squish along with some more porting.
July 8, 2010
I got a chance to check the jetting. I took the stock jet out and found it to be a 103. I found that I had a 110 in my kit and was pleasantly surprised that it made the bike fourstroke, definitely too rich. I have a 98 but didn't try it. Other than turning the idle mixture in it seems pretty good. I did a ride and found that I didn't gain much at full throttle until after an indicated 40. It will cruise at 40 at about 60% throttle. At least it roughed in.
I have my pipe cut down to 30". It ran great on top end at 29" before and had a stronger mid range at 32" but was slower getting above 40mph. Not sure if want it at 29" again. An inch is about 400 rpm. I am measuring from piston face to the end of the rear cone.
My GPS was dead and didn't get a top speed run. I rode it around for about 8 miles. Once the stock speedo hits about 45 it is pegged and I can't tell what it is doing. I am sure that big bore riders see that all the time.
I am running 24 grams on my stock variator right now. I need a big socket to get my contra spring out.
I got a chance to check the jetting. I took the stock jet out and found it to be a 103. I found that I had a 110 in my kit and was pleasantly surprised that it made the bike fourstroke, definitely too rich. I have a 98 but didn't try it. Other than turning the idle mixture in it seems pretty good. I did a ride and found that I didn't gain much at full throttle until after an indicated 40. It will cruise at 40 at about 60% throttle. At least it roughed in.
I have my pipe cut down to 30". It ran great on top end at 29" before and had a stronger mid range at 32" but was slower getting above 40mph. Not sure if want it at 29" again. An inch is about 400 rpm. I am measuring from piston face to the end of the rear cone.
My GPS was dead and didn't get a top speed run. I rode it around for about 8 miles. Once the stock speedo hits about 45 it is pegged and I can't tell what it is doing. I am sure that big bore riders see that all the time.
I am running 24 grams on my stock variator right now. I need a big socket to get my contra spring out.
July 7, 2010
I have been monitoring the max speed that I get after about a 1/4th mile hill of 30 feet. In the past 3 weeks I have been testing a lot of variables with expansion chamber length, transmission settings and carburetion.
My first tests showed that I couldn't get the engine to come up on the pipe. I lengthened it from about 25 to 29 inches and it would come up on the pipe strong but even with 16.5 grams in the variator I could feel the engine get stronger from about 37 mph until it flattened out at 47.7mph. My pipe was getting cobbled up so I made a new pipe with a 32" length. The pipe comes on lower now and would pull to about 46. The only way that I know I am optimum is when I go past that point.
I knew my pipe is really too long for max speed now and plan on cutting my new pipe down some perhaps an inch.
I also am going to put in a stiffer contra spring and rebuild my variator with some decent weights. I may want more rpm with acceleration and want to make sure that the internal friction of the variator doesn't overcome the weights.
No matter which setup I used I encountered almost the same top speed. I calculated the port time area and it was decent for almost 13000 rpm. To me that pointed to the intake system. The reeds and carb.
My first tests showed that I couldn't get the engine to come up on the pipe. I lengthened it from about 25 to 29 inches and it would come up on the pipe strong but even with 16.5 grams in the variator I could feel the engine get stronger from about 37 mph until it flattened out at 47.7mph. My pipe was getting cobbled up so I made a new pipe with a 32" length. The pipe comes on lower now and would pull to about 46. The only way that I know I am optimum is when I go past that point.
I knew my pipe is really too long for max speed now and plan on cutting my new pipe down some perhaps an inch.
I also am going to put in a stiffer contra spring and rebuild my variator with some decent weights. I may want more rpm with acceleration and want to make sure that the internal friction of the variator doesn't overcome the weights.
No matter which setup I used I encountered almost the same top speed. I calculated the port time area and it was decent for almost 13000 rpm. To me that pointed to the intake system. The reeds and carb.
July 6, 2010
A myth busted?
For as long as I have read on this list I have been told that a 49 cc engine is better served with the stock sized 14mm carb. 70cc engines should have a stock (14), 17.5 or 19 mm carbs.
I can't explain why my 49 cc engine likes my 21 mm OKO carb. I can't say that it is tuned as it has had no tuning except in the idle range but it runs great with it. It was raining when I got off work so I started the engine, warmed it up a minute or so and was rewarded with stronger acceleration than with the stock carb. Just rode up and down the blacktop.
How could the tuners be wrong? My bike should fall flat on its face when i opened the throttle.
I can't wait to get a chance to play with the settings. Find out what makes it slower then go the other way.
For as long as I have read on this list I have been told that a 49 cc engine is better served with the stock sized 14mm carb. 70cc engines should have a stock (14), 17.5 or 19 mm carbs.
I can't explain why my 49 cc engine likes my 21 mm OKO carb. I can't say that it is tuned as it has had no tuning except in the idle range but it runs great with it. It was raining when I got off work so I started the engine, warmed it up a minute or so and was rewarded with stronger acceleration than with the stock carb. Just rode up and down the blacktop.
How could the tuners be wrong? My bike should fall flat on its face when i opened the throttle.
I can't wait to get a chance to play with the settings. Find out what makes it slower then go the other way.
July 3, 2010
Well I am about to step off into the aftermarket carb (21 oko)/49cc cliff. I got my aluminum manifold with larger carbon reeds. Amazingly each reed is 4 mm wider and longer.
I installed the carb and manifold then scratched my head about making up a throttle cable. I ended up welding up a bracket and splicing the stock pull cable to a new short cable.
The tuning game begins again:
At first the bike would run only on the choke. I started turning in the idle mixture till it started carbureting. Pretty soon it was idling and accelerating against the clutch. That is it for today. Will do more tomorrow or the next.
My pipe is long at present It is 32.5" from the piston to the back of the rear cone. I was getting decent top end power when it was 29" I cut out all the small segments and welded in a 12" piece of 3" muffler pipe, before it is done I may be back to about 29". I have some new parts for tuning the transmission.
I'll share where this takes me.
I have tuned the OKO carb before and really thought it was a good value, with flat slide and std Keihin main jets.
Well I am about to step off into the aftermarket carb (21 oko)/49cc cliff. I got my aluminum manifold with larger carbon reeds. Amazingly each reed is 4 mm wider and longer.
I installed the carb and manifold then scratched my head about making up a throttle cable. I ended up welding up a bracket and splicing the stock pull cable to a new short cable.
The tuning game begins again:
At first the bike would run only on the choke. I started turning in the idle mixture till it started carbureting. Pretty soon it was idling and accelerating against the clutch. That is it for today. Will do more tomorrow or the next.
My pipe is long at present It is 32.5" from the piston to the back of the rear cone. I was getting decent top end power when it was 29" I cut out all the small segments and welded in a 12" piece of 3" muffler pipe, before it is done I may be back to about 29". I have some new parts for tuning the transmission.
I'll share where this takes me.
I have tuned the OKO carb before and really thought it was a good value, with flat slide and std Keihin main jets.
June 29, 2010
I have been noticing that my bike runs better on top end after a few 1/4 mile blasts. I was initially figuring that my variator is changing do to heat. It very well might be. I was running some calculations and noticed that as I changed the air temperature upward I was getting a higher peak in the order of 400 rpm increase for every 75 degrees. Guess my test runs need to be longer. Makes me appreciate the importance of having a lot of data collection that I am lacking. Gonna just have to rely on the butt dyno.
I have been noticing that my bike runs better on top end after a few 1/4 mile blasts. I was initially figuring that my variator is changing do to heat. It very well might be. I was running some calculations and noticed that as I changed the air temperature upward I was getting a higher peak in the order of 400 rpm increase for every 75 degrees. Guess my test runs need to be longer. Makes me appreciate the importance of having a lot of data collection that I am lacking. Gonna just have to rely on the butt dyno.
MacGyvering my Zuma
June 27, 2010
I got my expansion chamber cut apart again tonight. Figure that I would lengthen the belly of my chamber to see what it did. I got a new piece of pipe without the multitude of welds. I got greedy and increased the center section another 3.5". Giving me about 32.5" from the piston. That was too much. Great low up to about 35 then some strain up to 43. I figure that at about 35 mph I was past the edge of variator and in the overrev mode. I want the power to be there. Gonna cut it down 3"
While I had it apart I decided to take a photo of the inside stinger. It is picking up the exhaust air from the fat part of the expansion chamber (a low pressure area) rather from the end with higher pressure and noise.
I got my expansion chamber cut apart again tonight. Figure that I would lengthen the belly of my chamber to see what it did. I got a new piece of pipe without the multitude of welds. I got greedy and increased the center section another 3.5". Giving me about 32.5" from the piston. That was too much. Great low up to about 35 then some strain up to 43. I figure that at about 35 mph I was past the edge of variator and in the overrev mode. I want the power to be there. Gonna cut it down 3"
While I had it apart I decided to take a photo of the inside stinger. It is picking up the exhaust air from the fat part of the expansion chamber (a low pressure area) rather from the end with higher pressure and noise.
The weirdest thing last evening was that in the quest for more performance I put in my 110 Mikuni jet. Every time in the past that I tried using the 110 jet I would get nothing but too rich four stroking.
Last evening I was rewarded with a clean running engine with a bit more acceleration. The ambient temperature here was still close 90 degrees with high humidity. Does the 120 jet need to be tried? Guess I had better get one.
Jennings speaks to this in his book. He shows this graph of typical behavior of an expansion chamber:
I have been adding 2 inch sections to my pocket bike pipe. I have been using an old standard LP tank for my tubing. I basically have the full length of the tank inserted on my pipe. I figure that if I richen the jetting and get away with it I could be either lowering or raising the resonant frequency of my pipe as I may be increasing or lowering the exhaust temperature.
I would really like to cut the chopped up part of my expansion chamber (It is so ugly) and put in a new piece of pipe but figure that I had better work on the jetting first. Form follows function. Depending on temperature of the exhaust I am around 11000 rpm at peak power. I don't think that 48 mph is 11000.
Much to do!
Last evening I was rewarded with a clean running engine with a bit more acceleration. The ambient temperature here was still close 90 degrees with high humidity. Does the 120 jet need to be tried? Guess I had better get one.
Jennings speaks to this in his book. He shows this graph of typical behavior of an expansion chamber:
I have been adding 2 inch sections to my pocket bike pipe. I have been using an old standard LP tank for my tubing. I basically have the full length of the tank inserted on my pipe. I figure that if I richen the jetting and get away with it I could be either lowering or raising the resonant frequency of my pipe as I may be increasing or lowering the exhaust temperature. I would really like to cut the chopped up part of my expansion chamber (It is so ugly) and put in a new piece of pipe but figure that I had better work on the jetting first. Form follows function. Depending on temperature of the exhaust I am around 11000 rpm at peak power. I don't think that 48 mph is 11000.
Much to do!
Getting it running better, much better. I added another 2 inches to the body of the chamber. I didn't think that I was that close on what it took to get it "on the pipe". It accelerates stronger than I have felt it before now. I have my head pipe set at a medium length so need to try it shorter and maybe longer.
My Variator is funny. RPM stays high till about 30 where the rpm drops some till about 35 when it goes again. I think I am ready for a heavier contra-spring and some decent weight in the variator.
My pipe has way too many welds and a rather cobbled up mount, probably typical for many prototypes. The next version will look cleaner.
As others have said I should put a big bore for more speed but then I would get no satisfaction in knowing that I had done it myself.
I have a spread sheet showing some of my data on my 49cc. Ask.
My Variator is funny. RPM stays high till about 30 where the rpm drops some till about 35 when it goes again. I think I am ready for a heavier contra-spring and some decent weight in the variator.
My pipe has way too many welds and a rather cobbled up mount, probably typical for many prototypes. The next version will look cleaner.
As others have said I should put a big bore for more speed but then I would get no satisfaction in knowing that I had done it myself.
I have a spread sheet showing some of my data on my 49cc. Ask.
MacGyvering my Zuma
June 24, 2010
I got version 3 of my pipe up and running.
I mentioned that the pipe had a narrower powerband. I spent some time working on tuning it. At first I thought that I had jetting issues and went up and down with the my range of jetting. I am back up at my Mikuni 100 jet for now. Nothing I did with the jetting would let it run on the pipe.
I went ahead and drilled my stock weights down to 5.5 grams from 6.5 grams. I am only running three of them. My contra spring is stock. I put in some heavier clutch springs.
It is far from acceptable but I can get the engine on the pipe at about 25 mph and it pulls pretty hard, I have had it to 45. There is some strangeness in the jetting that gets better as the speed builds.
My big head pipe and matched exhaust port I think is the the reason that my low end is weaker. It does feel like the pipe comes on harder than the old one did.
Here are some photos of my work today.
I got version 3 of my pipe up and running.
I mentioned that the pipe had a narrower powerband. I spent some time working on tuning it. At first I thought that I had jetting issues and went up and down with the my range of jetting. I am back up at my Mikuni 100 jet for now. Nothing I did with the jetting would let it run on the pipe.
I went ahead and drilled my stock weights down to 5.5 grams from 6.5 grams. I am only running three of them. My contra spring is stock. I put in some heavier clutch springs.
It is far from acceptable but I can get the engine on the pipe at about 25 mph and it pulls pretty hard, I have had it to 45. There is some strangeness in the jetting that gets better as the speed builds.
My big head pipe and matched exhaust port I think is the the reason that my low end is weaker. It does feel like the pipe comes on harder than the old one did.
Here are some photos of my work today.
It is tacked up not finished final length is still open. I haven't welded the expansion chamber to the head pipe, it is a slip fit for now.
I am now thinking of a heavier contra spring.
I am now thinking of a heavier contra spring.
MacGyvering my Zuma
June 20, 2010
I have been analyzing my stock zuma cylinder and came to some interesting conclusions.
I have measured the port time-areas as outlined in Jennings. My exhaust port is pretty close to stock at the piston and is about 400mm square. When I calculated the port time-area as he outlined it 40 years ago, I came up with enough exhaust breathing for 10,400-11,800 rpm.
Of course the real problem with the exhaust port is that the port is very retrograde. Instead of gently widening say 10% from the piston face it got dramatically narrower. It really hoses down the power and makes a pipe rather ineffective.
I have also checked the transfer port time area and it seems pretty good for the rpm noted above. At this point I don't plan on widening the transfers but am using my riffler files to smooth them.
I plan on widening the exhaust port further at the junction of the head pipe. Stock is something like 14 mm high. Raising the top of the port really puts the angle askew to a stock head pipe. I have opened the top and depending on how you measure it I am now about 21 high and 24 wide. I plan on making a stub exhaust flange and centering it at the port about 24 mm wide. The angle that the port opens to the face is quite an angle now so I'll have to compensate for it.
The stock head pipe is about 21 mm ID at the flange and gets smaller at the first bend. It does gradually widen again.
I figure that the stock piston should tolerate the 11000 rpm and maybe higher, if a 47mm bore engine can tolerate 10,000 rpm.
I'll report back once I get the engine back together again. Much to learn.
I have been analyzing my stock zuma cylinder and came to some interesting conclusions.
I have measured the port time-areas as outlined in Jennings. My exhaust port is pretty close to stock at the piston and is about 400mm square. When I calculated the port time-area as he outlined it 40 years ago, I came up with enough exhaust breathing for 10,400-11,800 rpm.
Of course the real problem with the exhaust port is that the port is very retrograde. Instead of gently widening say 10% from the piston face it got dramatically narrower. It really hoses down the power and makes a pipe rather ineffective.
I have also checked the transfer port time area and it seems pretty good for the rpm noted above. At this point I don't plan on widening the transfers but am using my riffler files to smooth them.
I plan on widening the exhaust port further at the junction of the head pipe. Stock is something like 14 mm high. Raising the top of the port really puts the angle askew to a stock head pipe. I have opened the top and depending on how you measure it I am now about 21 high and 24 wide. I plan on making a stub exhaust flange and centering it at the port about 24 mm wide. The angle that the port opens to the face is quite an angle now so I'll have to compensate for it.
The stock head pipe is about 21 mm ID at the flange and gets smaller at the first bend. It does gradually widen again.
I figure that the stock piston should tolerate the 11000 rpm and maybe higher, if a 47mm bore engine can tolerate 10,000 rpm.
I'll report back once I get the engine back together again. Much to learn.
MacGyvering my Zuma
Here is the expansion chamber as it was on June 17, 2010
Here is my new head pipe compared to the stock headpipe.
Here is my new head pipe compared to the stock headpipe.
MacGyvering my Zuma
June 16, 2010
I did some trial runs with my elongated and silenced expansion chamber. Pickup was better but it still hit a wall at 46 mph. I am guessing that the breathing of the engine is well.... out of breath.
I have been using the stock head pipe about 8" long and tapered, starting at 19mm. (which should be a good thing.) It is made for a 35-40 mph design with midrange. According to Jennings the headpipe should be no more than 8x the port diameter in length. I am at about 10-12x at this point.
I need better breathing. My plan now was to make a new head pipe of one inch ID. I worked on making a flange and curving the headpipe, I cut several small pie wedges of pipe and welded them together. I stuck it on and realized that the centerstand is right where I want the pipe to run. Time to switch projects.
No problem I hated the centerstand from the minute I got this bike.
I have made side stands before and have used two sections of square tubing. The outer is one inch and the inner is 3/4". I welded the larger onto the frame tube where many of others have bolted or welded on plates.
My new stand tucks in great. It is recessed completely. I will take the lower plastic off so that I can weld the lower seam.
My new expansion chamber languishes tonight, and will perhaps for another week. At least I have a flange and headpipe.
I know pictures. let me see what I can do. I will definitely get a photo of my current expansion chamber before I cut the heck out of it.
I did some trial runs with my elongated and silenced expansion chamber. Pickup was better but it still hit a wall at 46 mph. I am guessing that the breathing of the engine is well.... out of breath.
I have been using the stock head pipe about 8" long and tapered, starting at 19mm. (which should be a good thing.) It is made for a 35-40 mph design with midrange. According to Jennings the headpipe should be no more than 8x the port diameter in length. I am at about 10-12x at this point.
I need better breathing. My plan now was to make a new head pipe of one inch ID. I worked on making a flange and curving the headpipe, I cut several small pie wedges of pipe and welded them together. I stuck it on and realized that the centerstand is right where I want the pipe to run. Time to switch projects.
No problem I hated the centerstand from the minute I got this bike.
I have made side stands before and have used two sections of square tubing. The outer is one inch and the inner is 3/4". I welded the larger onto the frame tube where many of others have bolted or welded on plates.
My new stand tucks in great. It is recessed completely. I will take the lower plastic off so that I can weld the lower seam.
My new expansion chamber languishes tonight, and will perhaps for another week. At least I have a flange and headpipe.
I know pictures. let me see what I can do. I will definitely get a photo of my current expansion chamber before I cut the heck out of it.
Jue 15, 2010
Last night I got a chance to work on my silencer. I left a stub of the new stinger hanging out of the back of the chamber (Most of it is buried inside it.) I had half of a late model YZ silencer in my shop. I welded end caps on the silencer. The stinger was small enough to just let the silencer slide over it.
I held the silencer over the stinger on the running engine and have to admit that it really mellowed out the tone. Nothing like the racket of the pocket bike chamber I started with.
I need to grind down some on the silencer to finish it up and then will weld it onto the expansion chamber.
I held the silencer over the stinger on the running engine and have to admit that it really mellowed out the tone. Nothing like the racket of the pocket bike chamber I started with.
I need to grind down some on the silencer to finish it up and then will weld it onto the expansion chamber.
MacGyvering my Zuma
May 26,2010
I went out tonight with my Garmin Foretrex and found that I could go 47 one direction and 45 the other. I did go 49.3 in front of my house on a short hill, I would like to say that my bike would do that on flat but isn't true yet. My speedometer is very accurate in the range that it is calibrated.
I am not disappointed in the least At this point I have 30 dollars worth of jetting and a 25 dollar expansion chamber. My jetting steps are in 10s and perhaps there is a bit more by trying some alternate setting. My bike idles well as you would expect. it pulls evenly. I have had my mixture all over. I have tried full rich on the needle and very rich on the main that I could only barely clear. I stay away from lean. My exhaust port was whittled in place and is not ideal. My belt is worn.
I have a new belt coming and will try lighter rollers when I am changing the belt. I have thought about making my own reeds I have the materials and carbon fabrication knowledge. It might be a bit tedious cutting them out with a dremel. I saw some available for 30 dollars.
I would like to see my bike go 50 or better on a stock bore. It may take a jug removal. I won't be working on my bike for a while, going to our farm for vacation. Will be riding my dirt bike.
I am not disappointed in the least At this point I have 30 dollars worth of jetting and a 25 dollar expansion chamber. My jetting steps are in 10s and perhaps there is a bit more by trying some alternate setting. My bike idles well as you would expect. it pulls evenly. I have had my mixture all over. I have tried full rich on the needle and very rich on the main that I could only barely clear. I stay away from lean. My exhaust port was whittled in place and is not ideal. My belt is worn.
I have a new belt coming and will try lighter rollers when I am changing the belt. I have thought about making my own reeds I have the materials and carbon fabrication knowledge. It might be a bit tedious cutting them out with a dremel. I saw some available for 30 dollars.
I would like to see my bike go 50 or better on a stock bore. It may take a jug removal. I won't be working on my bike for a while, going to our farm for vacation. Will be riding my dirt bike.
MacGyvering my Zuma
May 25, 2010
Considering that the engine definitely picks up power at 30+, even with 19.5 grains I am going to go lighter My next trial with the gearing is to bore the stock weights with a 3/8" drill. Right now the center hole is 8.8 mm and a 3/8" is 9.5mm. The OD of the brass is 11 mm. Since I am only using 3 weights I will have two sets with one being lighter than the other.
I also measured my belt. I presume that it was the original belt on the scooter. Has 2000 stock miles. My belt was 15.3 mm wide. Stock width is what 16.5. Time for a new one. Am I right in presuming that the increased width will increase the tension opposing the contra spring. More rpm?
I don't presume to have that much knowledge about 2 strokes, I think the 50cc scooter is the last stand for two strokes in the USA. What I do understand is math. I use it every day in my business.
Considering that the engine definitely picks up power at 30+, even with 19.5 grains I am going to go lighter My next trial with the gearing is to bore the stock weights with a 3/8" drill. Right now the center hole is 8.8 mm and a 3/8" is 9.5mm. The OD of the brass is 11 mm. Since I am only using 3 weights I will have two sets with one being lighter than the other.
I also measured my belt. I presume that it was the original belt on the scooter. Has 2000 stock miles. My belt was 15.3 mm wide. Stock width is what 16.5. Time for a new one. Am I right in presuming that the increased width will increase the tension opposing the contra spring. More rpm?
I don't presume to have that much knowledge about 2 strokes, I think the 50cc scooter is the last stand for two strokes in the USA. What I do understand is math. I use it every day in my business.
May 23, 2010
I removed one weight from each lobe of the variator. I don't notice any vibration. I imagine that with only 19.5 gr I get the rpm up pretty fast. I doubt if it is optimum but it is a Sunday and I am in the middle of no-where. I am not worried about focking up a 900 dollar scooter. The lightweight piston should turn lots of rpm.
Between my wife and I we have 4 other two strokes including my prized 83 RZ and 75 RD 350s ex roadracers, both were purchased new, I quit racing them in 1984, life took over. She has a 50 Suzuki 5 speed and a Honda Elite with an 86cc stroker. I put a CR80 pipe on it. My current street bike is a Yamaha SR500, it will do the ton on a good day and has loads of midrange. I have sold all my big bikes, what is the challenge of making a 165 mph bike faster? I want to ride hard and get no tickets.
I removed one weight from each lobe of the variator. I don't notice any vibration. I imagine that with only 19.5 gr I get the rpm up pretty fast. I doubt if it is optimum but it is a Sunday and I am in the middle of no-where. I am not worried about focking up a 900 dollar scooter. The lightweight piston should turn lots of rpm.
Between my wife and I we have 4 other two strokes including my prized 83 RZ and 75 RD 350s ex roadracers, both were purchased new, I quit racing them in 1984, life took over. She has a 50 Suzuki 5 speed and a Honda Elite with an 86cc stroker. I put a CR80 pipe on it. My current street bike is a Yamaha SR500, it will do the ton on a good day and has loads of midrange. I have sold all my big bikes, what is the challenge of making a 165 mph bike faster? I want to ride hard and get no tickets.
I slapped some paint on it. I probably will add a second brace but it works.
MacGyvering my Zuma
Posted 5/22/2010
MacGyvering My Zuma.
Today I was working on my bike. I made a right angle rubber intake manifold and a half inch thick open foam sock. I am running it dry although I think some light oil might be better filtration.
I also decided that the day was the day that I should cut off my stock muffler and weld on my pocket bike chamber. The stock head pipe is tapered so I figured that I should cut off the intake pipe on my expansion chamber and weld the stock tapered head pipe onto the diffusion cone. Some technical difficulties ensued. My mig welder was not available so I used my conventional stick welder. The chinese expansion chamber is very thin walled but I got it done.
Spent time working on my jetting. I found with the expansion chamber I could barely get the bike past 25 mph. Just couldnt get the revs up. The silencer had a restriction in it. I took the silencer apart and ground it out.
Thought that I would MacGyver the transmission. I looked at the weights that I had at hand and found that I didn't have any
. Ok my plan was to remove 3 of the weights. Wow what a difference that made. Revs cam up. I weighed my weights and they were about 6.5 grams. I guess I am running 19.5 grams.
Once I got the jetting fairly close It would rev much better and really start coming on at about 15 mph. Once it got to the high 30's it would start pulling to about 45 mph.
During my exhaust tear down I noted the unusual exhaust porting. I can stick my finger in the exhaust port only to feel it get larger near the piston. I suppose that I should tear it down but I just may stick greased cotton in the port and dremel it for now.
My pile of ex Zuma parts is increasing. Gone is the plastic cover. I think I am going to cut off the case past the center bolt. It was full of belt.
More later.
I also decided that the day was the day that I should cut off my stock muffler and weld on my pocket bike chamber. The stock head pipe is tapered so I figured that I should cut off the intake pipe on my expansion chamber and weld the stock tapered head pipe onto the diffusion cone. Some technical difficulties ensued. My mig welder was not available so I used my conventional stick welder. The chinese expansion chamber is very thin walled but I got it done.
Spent time working on my jetting. I found with the expansion chamber I could barely get the bike past 25 mph. Just couldnt get the revs up. The silencer had a restriction in it. I took the silencer apart and ground it out.
Thought that I would MacGyver the transmission. I looked at the weights that I had at hand and found that I didn't have any
. Ok my plan was to remove 3 of the weights. Wow what a difference that made. Revs cam up. I weighed my weights and they were about 6.5 grams. I guess I am running 19.5 grams.Once I got the jetting fairly close It would rev much better and really start coming on at about 15 mph. Once it got to the high 30's it would start pulling to about 45 mph.
During my exhaust tear down I noted the unusual exhaust porting. I can stick my finger in the exhaust port only to feel it get larger near the piston. I suppose that I should tear it down but I just may stick greased cotton in the port and dremel it for now.
My pile of ex Zuma parts is increasing. Gone is the plastic cover. I think I am going to cut off the case past the center bolt. It was full of belt.
More later.
Subscribe to:
Posts (Atom)