Ok I purchased a 01 SP500 a few weeks ago for parts,the original owner said he parked it after taking it to the dealer and they wanted $600 to replace the cam.I bought it home and decided to try to start it and it run but only at part throttle any more it would bog and die unless the throttle is released but idled perfect.I tore the carb apart and it looked good but cleaned it anyway,put it back on and same thing.I pulled the valve cover and sure enough the exhaust lobe had a good deal of wear so I replaced it along with the ex. rocker, adjusted the valves and it still does the same thing.I took the diaphram cover off the carb started it and pressed on the vacuum diaphram to prevent it from opening and the engine runs at a much higher rpm without any bog and of course no power that way but as soon as I pick up on the slide "lift the needle from the main jet" it dies but I cant tell if it is starving for fuel, getting too much or has another issue I'm over looking.This thing has wrecked my brain all day.I can even ride it as long as the diaphram is not allowed to open but wot is only 15mph

 

Does it have very high mileage?
make sure the exhust is not restricted?....(plugged)...........Caper.......

 

Hmm,not sure about the miles on it,the guy sold the pod. I'll disconnect the pipe at the rear in the morning to be sure it's not stopped up,didnt think of that.

 

I hated not to try to fix it,the engine runs fine,no knocks or smoke not to say it's not down on compression,anyone know the psi by chance,might as well check it as well

 

Most if not all small engine need at least 100 PSI to run.....If yours starts and idles fine...I would say your Comp. is good.......My guage goes into "RED color anything under 100 PSI.............Caper............

 

just a guess, but would it have a vacume issue? did you look at the spark plug to see if its running extremly rich/lean? you dont suppose the fuel pump isnt strong enough to supply the amount of gas required it needs at high rpm's. just a couple of idears to throw around.

 

I unhooked the pipe and that's not a issue,I'm thinking fuel pump too.If I let it idle for 5 seconds and gun it it revs perfect for just a split second and if I hold the throttle wide open it's up and down trying to reach a high rev but wont if that makes sense? Like I said if I let it set running idle for a few seconds it will rev like it should but only for a moment.I checked the fuel filter, actually bypassed it with no difference.I disconnected the fuel line while it was running off what fuel was in the bowl ,it pumps but has very little pressure and it takes for ever for the bowl to refill after it's dry. The line that comes from the pump and goes to the crankcase,is that suppose to have vacuum or does it push out air to run the fuel pump?

 

the fuel pump is run by vacume from the crank case i do beleave.

 

fuel filter, coil, plug wire?