Ignition timing effects on jetting ?

Andy86 wrote:

Been having some major issues dialing in the jetting on my 87 yz250 Constantly carbon and oil fouling new plugs within a few hours, it was...

Been having some major issues dialing in the jetting on my 87 yz250

Constantly carbon and oil fouling new plugs within a few hours, it was running really rich and the plugs were constantly wet

Tried loads of variation's of pilots, main jets and needle clip heights all not really having much of an effect

I gave up and decided to try a different approach and looked into the ignition timing, i borrowed a friends dial gauge and it turns out the ignition timing was a little off, the stator plate was to far to the left of the flywheel mark, according to my friend too advanced ?

So we moved the stator plate a few mm to the right of the flywheel mark retarded according to him ?

Now the the plug is nice and dry but white and seems to indicate a very lean mixture, you could smell the burning when riding

The needle clip was at the top notch, to try and combat the severely rich mixture from before the timing change, so we moved the needle clip to the middle notch and now plug seems almost right off white just starting to go brown

I have moved the needle clip to the lowest notch as rich as possible 5th notch down but haven't had a chance to test it yet

Once it stops raining i will test it and if the plug seems good i will swap to 360 main jet instead of the 350 thats in there now and put the needle clip back to the 3rd notch in the middle

Just wondering if any timing and jetting experts here have any thoughts or input on this ?

Im just shocked that the timing seems to have had such a major effect on jetting

To simplify stator plate too far to the left and jetting changes had no effect on plug condition

Yet moving the stator a few mm to the right and jetting changes are now having an instant effect on plug condition

Gone from plug covered in oil and lots of exhaust spooge, to a noticeable drop in spooge and an almost perfect plug, just slightly still lean

All just from a timing change and lowering the needle clip from top to bottom

Any replies greatly appreciated guys

mxb2 wrote:

Race shop section?

Andy86 wrote:

I thought about posting it there, but just figured it would gather more attention and hopefully more replies on the main board, if its not permitted...

I thought about posting it there, but just figured it would gather more attention and hopefully more replies on the main board, if its not permitted here i apologize for the inconvenience and could a mod please move it so i don't have to post it twice

Thanks for the reply though mxb2 its appreciated

HippieLogger wrote:

"White ain't right" advancing the timing as you have done has caused detonation. The white on the plug is vaporized aluminum from the top of the...

"White ain't right" advancing the timing as you have done has caused detonation. The white on the plug is vaporized aluminum from the top of the piston.

Set the timing and jetting to factory specifications as a starting point for tuning and make sure your running fresh gasoline of a high enough octane.

If you can't find high octane gas, consider lowering the compression ratio.

Since changing the needle height hasn't had an effect, consider a new needle? Just a guess here, maybe a leaner taper needle?

hillbilly wrote:

2 str are opposite of a car engine which is what is sounds like friend is going on. You made it fire sooner ,right? I'd say...

2 str are opposite of a car engine which is what is sounds like friend is going on. You made it fire sooner ,right?

I'd say the crank seal on the clutch side is really the problem,letting oil in as it fails.

Remember,the main jet is the dangerous one,you go smaller on it and risk seizing.

You can also seize with small pilot on long downhills where the throttle is closed and rpm is high starving the engine of lube and cooling fuel spray.