2-stroke/single-speed...operation for topend performance?

augidog

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Apr 20, 2008
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golden eagle system, 14tooth drivegear, 60lb bicycle/195lb rider...topend of 37mph...

tanaka 32cc purefire, upgraded to 12mm carby (from 10mm) & boost-bottle. stock crank and porting. E3 spark plug and tuned stinger extension (on stock converter/muffler) are pending.

the main reason for the carby-upgrade was tunabilty, as it has the high-rev mixture screw available...when the rear wheel is off the ground (no load) i can make it scream in either a lean or rich condition, but under load neither (extreme) setting will pull worth a dang. i'm hoping the E3 plug will help me with that.

with no gearing, the engine has to be kicked in by the time i've pedal-assisted up to 20mph, and it has to be tuned to achieve maximum rpm from there...i have a mile to reach topend, but it doesn't seem as if i need that much room.

so, what should i do? i added a piece of tubing to the screw so i can adjust mixture while running under load, but i'm noticing no real bump in maximum performance, there seems to be only one setting that makes it right for all conditions.

am i missing something or am i just going to have to admit i've hit the ceiling for this engine? is the boost-bottle (which is about 1/3 too large by volume) affecting topend?

i look forward to some serious discussion about carby-settings, boost-bottle, possible high-perf fuel...no need to tell me to start shaving metal off, no internal mods will be done on this engine...remember i need to be able to road-ride this when i'm finished racing, i can't be blowing it up...thanks :cool:
 
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J

Jim H

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Augi, have you seen the offset woodruff key that advances the timing on these motors? They increase engine rpm...think I saw them on some scooter sites that use these type engines.
 

augidog

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i have seen 'em, have been looking at some karting sites where tanaka seems to be quite popular, and have pondered the mod for a future build, but there doesn't seem to me much benefit unless there's some porting involved...and i get plenty of revs, i just can't seem to create any more power in the combustion chamber.

my goal this time out is to showcase a "stock" engine/drivetrain...the larger carby isn't really a bump if one were to gear down and go after more torque at 30mph. i could climb a tree with the 12tooth drivegear...

next year? well, we hope after our showing this year to attract some serious sponsorship...
 
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ocscully

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Jun 23, 2007
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Rpm?

Augie,

Any chance you have the RPM at which that 37mph was recorded? jpilots ratio calulator would indicate 9100+ rpm. Do you feel you were reving that high? The numbers I used in the calculator are the 14t driver you mentioned and then I calculate the GEBE Sheave to be the equivlant of 267t for a total reduction in the 19:1 range. Please don't take this question as me saying that you are wrong or in error I'm still just trying to understand the differences in reported top speeds and the math used in ratio calculator.

ocscully
 

augidog

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maybe santa will bring me a "tiny-tach" next x-mas, but...

yup, i'm getting some good revs...dennis says the engine can handle approx 12k, but putting some power behind the revs is a different story...
 

augidog

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so...this isn't like an engine that would be asked to perform throughout it's range...but only as rpm's increase...like i should be able to make fine-tunage as momentum steps in...much to learn.

any tips, secrets, links?
 
L

Large Filipino

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I'm no expert but it sounds like you're hitting a dead spot at speeds?
Sometimes dropping the gear by just a tooth can help that rut even if it means higher RPM on top.
Like when I read car magazines on top speed runs. Most cars top speed happens at a lower gear than what the tranny has in gears. Fourth gear gets you to top speeds but when they shift to 5th it drops.
It would be cool if you can hook up your engine to a dyno then you know at what RPM your engine is making the most power. Then you gear according to that RPM,to get you to top speed at that RPM.
 
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augidog

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changing drivegears takes only seconds, and worthy of experimenting...thanks fer knocking my brainpan around...tune for fat r's but drop down to give it more advantage, sounds like fun...i know we're only guessing, but it feels right :cool:

no real ride-time this weekend, tourist influx for a "clam-tide", i'll lay low until monday and get fresh fuel, maybe my E3 plug will be at the post office then...

one thing, there is a custom 16tooth heading my way, so i need to find the most powerful top speed under the current load, then hope i can still squeeze a bit more when i gear up..whatever happens, i will let ya know, tho :)

anyone who has the tip i need to maximize performance once i reach maximum r's, or to find that balancing point, please clue me in.
 
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augidog

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for anyone who really wants to get into it, here's the pdf i got from walbro's site...not sure if it's the exact one, but the construction and illustrations are:
 

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