Leans out in midrange

[rcklobster]

Hello again!

I finally got my 650 up and functional and am now working on fine tuning everything. The only problem I have now is a definite lean spot from about 4k to 6k RPM. This only happens in midrange throttle, if you baby it along, it won't lean out, and if you twist it it will power through it.

Any ideas?

Also, there is a slight increase in valvetrain noise when it leans out.

Thanks!

[Nessism]

Is the bike stock?

Have you performed all the various maintenance tasks? Clean the carbs? New O-rings in carbs? New intake boot O-rings? Vacuum sync the carbs? Valve adjustment? Airbox sealed w/fresh filter (that is also sealed to the airbox)?

[posplayr]

he probably has a 4:1 and is feeling the flat spot due to reversion

[chef1366]

That's not valvetrain noise. That's pinging! (detonation) http://en.wikipedia.org/wiki/Engine_knocking
Shim that needle or get a Dynojet needle. You need to richen that needle and fast or you may hurt something.
If you need to ride it and can't fix it right away retard the timing a few degrees.

[rcklobster]

To be completely honest I don't know if it is stock, it appears to be, but who knows.

Pinging, you say? Well that isn't good at all. I will have to pull the carbs and try to shim the needle and see what happens. Any idea how much I should shim it? Or at least a good place to start?

Thanks for all of the help!

[chef1366]

Get some Assorted small washers from Radio Shack.
Take off the plastic spacer over the jet needle.
Stack the washers the same heigth as the spacer. Take away two to start and replace the plastic washer with those washers.

[rcklobster]

Will do. Thanks for the info hopefully the problem will be corrected.

[trippivot]

normal needle adjustments are 0.5mm or about 0.020"

[Willmrx]

Had the same issue with my 1981 GS650G. I rebuilt the carbs using K&L carb kits. And I just removed the plastic spacer and I put a washer on top of the c clip, the same size as the one that retains the needle spring. Went for a 80 mile plus ride, no more noise and the bike pulls stronger in the 3500 rpm to 5500 rpm range!


Will