pulsing idle on 96 yz need some ideas

[cuban b]

I got this yz that ran like junk. I cleaned the carb and now it is running pretty well except the idle is funny. It doesn't always stay idling, but the main thing is a quick pulse. The RPM's go up a little every half second or so. I'm not sure what would cause this.

any help is appreciated, thanks

 

[rholbrook]

Too small of a pilot

 

[AaronPaige]

If your fuel is to low of octane it will bun to fast and cause it to run rough especially two strokes don't like the new mixed fuels, or sucking air around your reeds could do it... Lots of causes can you run the idle up a little and have it smooth out?

 

[cuban b]

sucking air is a possibility. or the jets. I'm not very experienced with bikes, so I'm new to jetting. I don't think it's the gas because it doesn't really run roughly, it's pretty smooth but revving slightly.

So how would too small of a pilot cause a pulse, and not just a constant "wrong" amount of gas?

 

[Rot Box]

I agree too small of pilot jet or the pilot circuit is not completely clean. You can adjust the fuel screw on the side of the carb (this fine tunes the pilot jetting). Turn it in all the way and count how many turns (helps to write it down for future reference). Then turn it out 3 turns and see if that makes an improvement. This is the small brass screw not to be confused with the idle adjustment screw. Keep in mind it is only efficient between .75 and 3 turns out. Out is richer--in is leaner. If you need less than .75 turns install a smaller pilot jet. If you need more than 3 turns install a larger pilot jet. Does that make sense?

If the jet doesn't fix it there's the chance it could be sucking air as Aaron mentioned. Reed valve gaskets, base gasket or crank seals may need to be replaced. Gas should be fresh, air filter should be clean and the spark plug should be fairly new before any major changes in jetting. Hope this helps,

Andrew