I have an 88 250r that is ported and polished with a fmf fatty gold series and a keihin pwk 39mm...which I finally got tuned for my silencer with no spark arrestor, but i went riding yesterday and I had to put on a new fmf silencer with a spark arrestor and now my bike runs terrible. It was back firing every once and a while, bogging down below quarter throttle, and cutting out and dying at low speeds. I figured that the clip was too lean so I richened it up and it wouldn't even go, it kept dying. So I leaned the clip all the way out and it ran better, well it ran great at full throttle, but it would die as soon as I backed off the throttle. Please help me. should I get a longer needle?

 

It does sound like jetting, but the fact that you played with the needle setting already leads to something else. It could be the pilot jet, but that doesn't really control much. Have you checked to see if you have an airleak or anything? You may also have a bad spark plug. I know it seems simple, but you should try a brand new correctly gapped plug, even if the one you are using seems to be brand new. It is probably something really simple.

 

So Am I running too lean, or too rich?? Should I change my needle length or my pilot jet or something else. I don't have an air leak, I checked that earlier and It ran OK.

 

Check that the spark arrestor screen (if equipped) isn't clogged. Or that the packing has come lose and is obstructing the outlet. If it's a FMF Turbine core there's no screen, but packing can block the outlet.

After that check all the simple stuff...good gas, new plug, air filter, tank vent.........

 

nothing is working??? please help me

 

well I think it has something to do with you needle since. well what does you plug look like? if its wet then go up a notch if it dry then go down. it shouldn't be hard to fix. later