Piston Wash - How Long?

[SkiDaddy]

Question for the tuners - How long does it take after a jetting change for the piston wash pattern to reflect the new mixture?

And do you check wash paterns like a plug chop at full throttle? Does the wash represent full throttle mixture, or just an overall average?

Finally, the jetting on both carbs (OEM38s on a RN) is identical, but there's significant variance from one cylinder's wash pattern to the other. Normal? (Professionally ported BTW).

Thanks.:smile:

 

[douglee25]

I've found it difficult to do a plug chop on a standup because first of all, they usually aren't ridden at full throttle for more than a second or two. The second reason is, new plugs tend to take a while to actually show color or variances of color. This can be the result of different gas additives from state to state or gas station to gas station.

A plug chop at full throttle represents that which is done at full throttle. Once you idle or run mid throttle, etc, the plug color is technically going to be off. The wash itself on the piston can take several rides for it to form. I ran a motor for about 10 rides that was way too rich. I didn't see any piston color whatsoever.

If the jetting on one carb to the next is identical, yet you have varying plug colors, it could be a couple things. Leaking head gasket (water intrusion), bad crank seal on that cylinder (lean condition), bad carb seal on that cylinder (lean condition), or even a leaky crankcase at the parting line. A pressure test would confirm a lot of this. If still the color is significatly different, I would think something is different in the carbs themselves. You may at that point have to jet differently.

Doug

 

[SkiDaddy]

Plug color is almost identical after just riding, no plug chops.

If you're way too rich it will leave the piston top clean.

 

[Idok]

bob....E always has told me about 30 sec's to a minute MAX to reflect changes.......


we dont often do WOT plug chops either.......

 

[SkiDaddy]

I agree on 30 seconds for a plug chop (if you can hang on that long!:bigeyes: ), but for piston wash I'd imagine it'd be much longer.

Weather looks crappy for the weekend so maybe I'll check top end jetting now that the bottom is good (stronger than ever!:Banane01: ).