kinda solved the problem with my 86r...

[dirtbike77]

lately i been having problems with the bike, it was running horrible... sputtering and cutting out... i also put a clucth update kit in it, but for some odd reason it would drag through the gears? i ended up putting the older push rod along with the other mechanism... that solved that problem.. i also put a new plug in it.. supported the coil correctly, removed the air box lid... the bike runs great... only one small problem... my 6th gear is still flat...first through fifth it rides real good... but when i put it in 6th gear it kinda loses power and even cuts out... i have a 148 jet in it.. could that be a problem?


heres a older pic of my bike... it looks alot diffrent now... im working on getting new pictures...

[tony_250r]

First, if I had a stock engine, I would put the air box lid back on. Running the stock engine without the air box lid causes loss of torque and sounds louder. If someone tells you they gained hp by running a stock engine, it was most likely due to them leaning the fuel mixture out.

You can gain the same hp by tuning the stock carb correctly. After you get the stock engine tuned, you can use air box vents for a leaner stock engine set-up.

What's up with your engine set-up, other that what looks like a FMF Fatty pipe?:
[list]
Do you have a stock bore, carb, air filter, reed valve and reed, porting and head?
What silincer are you running?
When was the last time you re-packed the silincer?
When was the last time you did a top-end "how many hours are on the piston"?
When was the last time you inspected the reed valve?
[/list:u]

[dirtbike77]

bored .80 over
fmf pipe
fmf silencer.
after mearket reeds, with 6 pedals..
just recently got the head shaved, along with a new top end rebuild.

[tony_250r]

I guess you conducted the spark plug test. On the 86 atc 250R the stock main jet is a 145. I would say you are within range using a 148 main jet with your set-up.
The best thing to do now is go up on the main jet, then make a test run. If richening it up helped or corrected the problem, then you are in the right direction. Always take the spark plug test after tuning or changing the main jet.

I know changing jets up and down is a drag. But that's the only way to isolate your problem. If changing the jets dose not correct the problem, we know to look somewhere else.

You have to jet way over, then work your way down. Doing it that way, you'll see exactly how the jetting is acting on the engine. There is no short cut.