moderateatvrider

hello everyone, got some problems with my bike that i need some help figuring out. when i start the bike itll run fine for 2-3 minutes, then it starts to rev really high(almost at max rpms) and doesnt respond right to throttle(sometimes throttle will bog it out doesnt do anything). The only way it can kind of control it (and it seems to work pretty well) is by plugging the breather hole/vent out of the bowl of the carb. When i plug that hole it stops reving really high(almost instantly) but the throttle now seems to stick(I hit the throttle and itll respond nicely but slowly idles down). Now ive cleaned out the carb around 4 times and blew it all out with an air compressor, so it should be well cleaned by now, it also now has a new diaphram installed as well. I do know that there is a bad valve(I think its the intake valve) because its got around 155-160 psi when engine is cold but once it warms up its a little under 120psi. Also think there is a electrical issue because the head light only gets bright on the last stroke as the bike dies out(No battery installed). Not sure if either of these problems could cause this but hoping someones been there done that and knows the root of the throttle problem. Also every time i check the spark plug its black and fluffy Thanks in advance for ur help.

Got the new chain in and its running alot better, also the valve timing is actualy staying where i set it, and didnt know it till now but the engine/valves before replacing the timing chain where making alot of noise/tapping but now i dont hear any noise coming from the engine, what a difference!!..Now Ive run into a new problem that i cant solve, after running the bike for about 15-20 minutes the spark plug is getting covered in black carbon, it also spits out black smoke when i hit the throttle..Is there any other part i should look at besides the air/gas mixture screw?, i set it at 2 1/2 turns out and adjusted it out a little at a time but it seems to have made no difference, now its probaly around 3 turns out but same smoke..Also i cant use most of the throttle, i can only use about a 3rd of the throttle and past that it starts to miss and sputter..ive also noticed that once in a while the bike will start to idle up pretty high out of no where but if i shake the bike it will go back to normal..wierd..but i know i cant be far now, just this last bit holding me up..Thanks in advance for any help, im pretty stuck at the moment..

finally got the cam chain in the mail, just waiting for rivet tool now..While im waiting i wanted to check and make sure the chain is the right one because i wont be able to compare it to the old chain the way im installing it by hooking it up to the old chain and slowly cranking the new one in and old out, so does anyone know the specs on what the chain should be??The new one i recieved is 25H-104L..hope its right..

Ya I'm gonna double check all the parts when I change out the chain, I'll be able to order the chain and rivet tool in the next couple days and I'll keep everyone posted on how it works out. Thanks for all the help. Fingers crossed

I checked out all the tentionerparts and all is in good shape and working flawless but noticed what I think might bethe problem, the tentioner is at its outmost position and when I place it back in its hole(still all set at its outmost position) its not touching anything inside, there's no tention on it, even if I hold it in place and crank the engine I can feel it push up very sporaticlly but mostly just sits there. So I'm thinking that the chain has streched past what the tentioner can handle but not sure if that's how its supposed to work. If so can a stetched chain cause te valves to tighten and loosen seemingly be themselves?? Thanks for the help.

Thanks mudflap64, ya it has an auto tensioner, never got to messin with it tho, but tried everything else so hope thats it..Any idea what problems to look for?,How do i know if it is bad?..thanks again for your help, might be able to ride this year after all..

Im having the exact same problem with a quadrunner 250. The vavles keep tightening them selves out of adjustment..Best I can figure is its a cam or chain problem but not sure which one..If you do figure this out please let me know what your cause was maybe itll be the same for me..Mine started out the same way but now itll only drive for 10 minutes until the vavles get too tight and it wont run any more, it really sucks..Hope u get ur answer.

Well as for the petcock some machines have a vac line to both that and the fuel pump, as is the case with the suzuki quadrunner 250, so make sure the lines are where they are supposed to be, those vac lines being hooked up wrong can cause all kinds of fuel problems. So the flooding could be alot of different issues, I would start checking the manual against all the new parts to make sure they are identical to what that engine needs. For example: The jets/ needle ports on the carb could be bigger then the engine can handle, or too strong of a fuel pump could cause issues. Next once all the replaced parts are checked against the manual especially All the carb parts, then i would start with the carb making sure that the float and needle are operating right, alot of flooding problems come from the float parts. *If carb float internals turn up no problems I would check all the choke parts(cable movement and all parts connected in the carb.) A stuck choke will flood it out and cause the engine to respond to the full throttle like you described. Hope this helps.

I would check the choke parts fisrt:make sure its working properly, i have a couple machines that dont have a choke and i have to start them with ether..If no problems there i would then say its a fuel delivery issue: an idle set too low for cold starts, or a problem in the small/idle port in the carb. Hope this helps..(also check the spark plug make sure its clean and working properly, sometimes we over look the simple things)

:aargh:I need a little help figuring out a vavle tightening problem im having with the bike. I adjust the valves with a feeler gauge, start the bike and ride for about 10 minutes then its starts to run really rough, check the valves and their now too tight, so i adjust them again run the bike for about 5 minutes and the bike starts to bearly drives now, check the valves and their too tight again...Now this happens to both intake and exhaust at the same time and approx the same amount of change. Also sometimes i go to start the bike after it starts to run rough (adjusting the valves back out because now thier to tight) after a couple pulls and it doesnt start i go to check the vavles again and they are wayy too loose, causing the bike to not start..Some how the valve timing/gap keeps changing..Could this be a cam or timing chain problem??They both looked good after visual inspection.Cant figure it out and need some help, any help is greatly appreciated, thanks.