Lean rear cylinder

Ernest Montague afm199 at earthlink.net
Fri Oct 2 09:34:07 PDT 2009

Pilot jet was completely clogged up, which explains the 2000-4000 rpm 
backfiring, overheating and crappy running.

On Oct 2, 2009, at 6:16 AM, Randy Grein wrote:

> There is a jetting differential front to back, can't remember for sure 
> which way - but sounds like you need to go up a size on the rear.
> Randy Grein, WMRRA #141
> On Oct 1, 2009, at 10:04 AM, Ernest Montague wrote:
>> My rear cylinder is running super lean for some reason.  The header 
>> interior is clean and light grey/white with no carbon. I am running 
>> pump gas, which always leaves my headers a bit black.  But the rear 
>> is very light colored, the front the normal blackish.  It's not a 
>> head gasket leaking water ( at least last time water got in the 
>> combustion chamber via head gasket it steam cleaned everything. The 
>> chamber just looks lean, valves very clean and grey/tan.  I looked 
>> for missing vacumn plug, bad slide rubber, plugged main jet, etc.  
>> The mains front and rear are 170s a range that has worked well in the 
>> past with the M4 system and BMC big mouth race filter (factory pro 
>> design).    Even if it was the main I can't believe it would be so 
>> different from front to back.
>> Also backfires and pops at cruising  2500-4000 rpm.
>> Bike is mostly ridden at full throttle on the track.
>> Suggestions?
>> Ernie

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