Resurecting the old 86

[CR250R@WINTERS]

Guys (or gals),
I need a little help here. I have an old bike that I have, but I am having a little trouble getting it to perform at its peak. The bike is a 1986 CR125R , the carb is clean and I have checked everything that I can think of. It starts great and seems to run strong most of the time. The one thing that I can't get ironed out is that if you go from an idle to full throttle as fast as you can twist it, the engine just boggs out until you let off the gas a little and then it takes off. If you apply the throttle slower it doesn't happen and runs fine at full throttle. Just seems to be with that quick twist that is the problem. I have checked the jets, the air cleaner, etc, etc. and can't find anything wrong. Need to check that old ATC valve yet. Any thoughts or suggestions would be greatly appreciated.

 

[Bodge]

Try a richer pilot jet or lower clip position on the needle, soulds like the engine is a bit lean. Check the atc valve 1st though.

 

[DEANSFASTWAY]

You could probably hold that ATC valve shut and you wouldnt know the difference until youre riding it , then i bet most people wouldnt even know its there .aftermarket companies used to sell a straight exhaust port spigot toreplace the whole thing back then . Id look at the redds while I have the carby off . Good luck , good bikle I had one back themn it was trick with the gold rims and all .

 

[MXP1MP]

I used to have one of those, mine was all pro circuit modded, check the jetting stock jetting was pretty close for that year it was pretty jetting fuss free. My procircuit modded bike did not have the ATAC in fact almost all the parts had been removed by the previous owner. Procircuit still offers a pipe for the bike and DG still has silencers. I used just regular boysen power flo reeds (epoxy resin (old skewl) kind with almost stock jetting. I think I leaned out the main from a 162 to a 160. and the air screw at 1.5 turns out but then again my bikes carb had been bored also! that bike had everything procircuit made then for it. Swing arm, alum subframe, porting, carb boring and suspenion revalved.

 

[MikeT]

Try a richer pilot jet or lower clip position on the needle, soulds like the engine is a bit lean. Check the atc valve 1st though.

Lean condition. Do what Bodge says.