Popping while idling

[jakeyz250]

Jetting problem???? Or Exhaust???

I have a 1990 yz250 that pops really loud while idling. A friend thought that my reeds were probley bad, so I put new boyesen power reeds in. Now its alot snappyer but it still pops. I have adjusted my AS but i can't get it to stop popping. The bike had a FMF Gold Series pipe on it, and when i checked out the settings in the carb, the main jet was as lean as possible, and the needlee clip was in the second position instead of the third. But that should have any effect on the idle setting. Could the problem be with the exhaust? I think the silencer is stock. Please let me know if anybody has any ideas. :bang: I have a 1982 yz250, and i think the jettings is probley standard on it. so mabey if that could be the problem,, i could switch out the main jet.

 

[cr2504life]

Did you try playing with your air screw? You mention that the main was lean as possible?? What do you mean? Maybe you could try a different pilot jet(richer).

 

[jakeyz250]

Yes, I did mess with the air screw. That doesn't make the popping go away. Well. What i am going by when i say that my main is lean as possible is my other yz 250 manual. which says that has a chart here of the main jet settings. Std. jet is #370 . and what is in the carb now is a #340. which the lower the number the leaner it is. When I put in my boyesen reeds. I changed teh pilet jet to what boyesen recommened. which was the third clip posiition. But after I ran the bike around. It ran like it never warmed up. you know what i'm saying, like it would cut out on me when I would give it too much throttle. So i changed it back to what it was, and it ran like a peach, exept for the popping.

 

[jakeyz250]

can anybody help??

 

[Joe_148]

hows the silencer packing? shouldnt matter but still..

have you checked the head gasket? ive heard that if you have a coolant leak the bike will pop..

 

[jakeyz250]

What is the packing supposed to look like. I thought about that once, and i took apart the silencer, but I don't know what its supposed to be like inside. I don't seem to have any coolant leaks. My oil never turned white, and my coolant level hasn't dropped at all.

 

[jakeyz250]

I switched silencers on my yz250's, and it still pops. Are there any other suggestions? Could it just be the way the bike sounds with the fmf pipe?

 

[a454elk]

Doesn't popping mean lean. Is there a chance you have an air leak on the engine side of the carb? Bad gas maybe? Does it run fine otherwise, throttle, etc? Do one change at a time, jetting, unless way off, probably wouldn't cause that. Clean out the gas and carb so you know you have a clean slate there. Spray carb cleaner around the bolts and boot where the carb meets the engine, if it dies, you're sucking in air. Let us know how things go.

 

[jakeyz250]

The popping has been a problem since at least the last owner had it. I have new gas in it, and I have cleaned the carb multiple times. Other than the popping, the bike runs fine. It has a lot more pep now that I put the Boyesen Power Reeds in. It also used to not start easily before I put the reeds in it. Now it will start right away. I will check for any air leaks tomorrow. Thanks

 

[matt-itude]

Just a thought guys but how about the crank seals and base gasket be included in the search for an air leak?

 

[jakeyz250]

I sprayed down the boot, bolts, gaskets... and now i have a clean engine, but it still pops! :bang: Mabey thats just how the bike sounds with this pipe... I would switch pipes from my 1982 yz to my 1990 yz, but the 1982 has the exhaust go out the left, and the 90 goes out the right.


Could a small crack in the pipe cause this. Or mabey if the engine itself has a small crack. Does aluminum hide cracks?? Would the bike run bad all around if it had a crack in it?

 

[gowen]

Years ago, I have a '86 yz250, smiler to yours, I also had the FMF fatty pipe and silencer, reeds, and also had alot of motor work, I had the bike jetted according to my local dealer who used to race and work as a pro mechanic in mx. and my friend, my YZ always popped. I would play with my ypvs timing and get the popping to go away, but would change the powerband at the time. Which is what I was looking for.

 

[a454elk]

A base gasket would not suck air in, probably lose oil through it from pressure. Electronics maybe?? Clean out the stater. Crack in pipe would be more of a tick, maybe popping on decel though.

 

[jakeyz250]

hey gowen.. Thats cool to knkow that i'm not alone...haha.. What kind of engine work did you have done? , Did it still pop when you changed the timing? what effects did it have on the powerband?

I will still check all the electronics though now... they should probley be checked now anyways.. Thanks

 

[jakeyz250]

Is there supposed to be old oil in witht the ypvs? My other yz doesn't have oil in there, .. And if there is supposed to be oil in there, I would think that it would be clean..!!!!?????

 

[matt-itude]

hey if your pulling the cover to check the electronics make sure you flywheel hasnt slipped a little out of time. I know the bike runs good but stranger things have happened

 

[matt-itude]

FYI if a crank seal can suck air so can a base gasket. both however are usually noticable by the oil pushed out. remember as the piston moves up vacuum (lower pressure) in the crank case draws air in under the piston through the reeds or anywhere it can get in (reed cage, carb flange, crank seals, etc) on the way back down the reeds close and then we have pressure usually causing a visible oil leak from the premix if a leak exists.

 

[jakeyz250]

i just wish i had one of the little tdc guages

 

[matt-itude]

alot of the time you can just pull the nut off and with a flashlight look inside where the flywheel key way is cut and see if the cut in the flywheel and crank are still lined up without pulling the flywheel.

 

[jakeyz250]

ok, i might have to check that out.. I always wanted to check the timing on my 82 yz, but never have..

Also, after i took off the cover for the powervalve, i could see that there is a notch in the arm deal, and nearby on the enigne, is another hole, should they line up?

 

[matt-itude]

your getting alittle indepth for me on the yzs as far as how the power valve is timed and actuated. also to make sure the key way is lined up dosent indicate your timing it just helps insure it hasent slipped from where it was set. Keep in mind just as you all have been talking that a highly modiffied bike doesnt run like a stock one at idle off idle, half throttle, full throttle etc. just like a funny car doesnt idle like a daily driver. not to discourage you because there is alot of things to be tried to tune this possible problem. and i (not that thats saying much) havent seen one that couldnt have a problem like you describe tuned out of it. Keep trying ond dont forget to go out and play a little.

 

[blackoutyz125]

Ignition timing, could have a sheard key. Pre-ingintion maybe. What does your spark plug look like after you take it outa the bike, color etc.

 

[Anssi]

How about turning out the idle screw until the bike only idles for a few seconds when you let off the throttle?

 

[jakeyz250]

The spark plug has always been dark, even though the bike runs awesome with the jetting towards the lean side.

Hey blackoutyz125, where do you ride?

 

[jakeyz250]

I don't know if it was like this before, but now when i turn over the engine, the powervalve seems to be pretty close to the piston. I don't know if it is actually hitting, but it makes the extenal arm for the powervalve move slightly. Did I mess something up, or did those tabs wear out? What is that special little thing you guys have done that fixes that? like grinding something down? Thanks