93 suzuki quadrunner 250 valve issue

[moderateatvrider]

: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.

[Mudflap64]

Not sure if your model has one, but it sounds like a malfunctioning automatic chain tensioner on the timing chain. I can see a little variance when the chain is worn but what you are describing sounds like ALOT of variance in opposite directions. See if yours has an A.C.T. Thats where Id be looking.

[moderateatvrider]

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..

[Mudflap64]

Not sure on your bike, but when I had a ACT fail it had a heavy spring inside it wich broke. The spring wound inside itself so the tension on the chain was constantly changing. Eventually the chain skipped & it pointed out the problem. Anothe rthing you should check is to make sure there isnt alot of wear on the tips of the valves or rockers. If theres a big groove worn into either it could caused the adjustment to loosen up & wander all over the place. Just a few of my thoughts.

[moderateatvrider]

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.

[Mudflap64]

Sounds like a stretched chain to me too. That could cause problems if when you are adjusting the valves the cam is not @ zero open position for the valves. If you are going by the TDC of the crank shaft mark, or even getting to TDC by piston position, the cam(s) may not be properly oriented. How much rotational slop is in the cam(s)? If the chain is that loose it could have jumped a tooth or even be jumping teeth back & forth. Another thing to note is if the valve timing is that far off or the chain has skipped teeth, you could possibly have a bent valve that is hanging up. Id be doing a serious inspection of all the cam timing components. It sounds like it might just be time for a rebuild. Keeep us posted.

[moderateatvrider]

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

[moderateatvrider]

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..

[moderateatvrider]

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..

[oxidized_black]

you might need a rebuild kit for the carb ... and/or a good carb cleaning ...