Is it possible to improve top speed without changing tire size or gearing? Here’s my dilemma, I have an 85 Yamaha Tri-Z 250 (2 stroke trike) which a few months ago only had a UNI air filter with the stock carb jetted (Mikuni VM 32mm) airbox lid on, Boyesen Pro Reeds and the stock pipe with an Answer silencer (similar to DG). When I raced my brothers Banshee (with FMF pipes, silencer, KN Filter and jetted carb) we were dead even from stop to top speed (roll start in pavement). Recently I installed an LRD pipe and silencer, a Mikuni TMX 36mm carb and rejetted it myself for no lid use. When I raced my brothers Banshee again with all my new mods I was as fast at low end but slower at top speed (Full Throttle). My brother has only added a cool head since then and I also raced a friend’s banshee and he was faster top speed so I do not think the cool head makes the difference. Is that possible or am I paranoid? How can I be slower after getting an aftermarket pipe & SILENCER AND a bigger carb without airbox lid? Am I missing something? What can I do to get more top speed?

 

your bike should deffinetly be faster now after those mods. i will take a shot at your prob. when you jetted your carb how did you do this. the reason i ask this is i think your bike might be lean on the main jet. if its lean on the main jet it will make power but not rev out and if it is really bad it will fall on it's face. what i suggest doing is putting in a bigger main jet untill it "blubbers" at full throtle. once you do this then go down on size on the main jet and it should be really close to perfect. i think this will fix your problem.

 

When I first jetted my main it was very rich (I was running a 470) and it would not run at all at full throttle the engine breaks up when at full throttle. Then I switched to a 440 and it ran fine at full throttle for about 4 seconds then make a small break but keep running strong, this was with the lid on. Then I remove the lid with the same 440 main and it ran great but I went down to a 420 main afret that to make sure it will run with no "blubbers" with and without airbox lid. Am I wrong? Should I go to 440 main again? Will that make a difference? I thought 2 sizes main will not make any difference!

 

Sweet bike!

 

Was that a torque pipe? If so that could very well be your problem. Try putting the stock pipe back on with you current jetting. And if that fails call JOHN at " Phils cycles & ATV " in El-reno OK. He is the Mechanic,he has a Tri-z that is very fast and it has great topend. he really like threewheelers so I think he will help you out.

Biggerisbetter.

 

I nearly forgot to add...

It's like on a naturally aspirated car, you can get a free flowing exhaust and gain top end power or you can go a little more restrictive, gain some back-pressure and have better low end...

It all depends on what you want or need...

 

<< When I first jetted my main it was very rich (I was running a 470) and it would not run at all at full throttle the engine breaks up when at full throttle. Then I switched to a 440 and it ran fine at full throttle for about 4 seconds then make a small break but keep running strong, this was with the lid on. Then I remove the lid with the same 440 main and it ran great but I went down to a 420 main afret that to make sure it will run with no &quot;blubbers&quot; with and without airbox lid. Am I wrong? Should I go to 440 main again? Will that make a difference? I thought 2 sizes main will not make any difference! >>



The only way to know for sure is to find the correct jet with the lid on. Then off. I think your lean with the method you used. I'd go back to the 440,(lid off). If it still breaks up consistantly try a 430. When you put the top back on it's going to be rich, no way around it. All you can do is put the jet back in that you found by testing.