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.
Friday, August 6, 2010
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!
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