View single post by Judson Manning
 Posted: 12-04-2007 04:34 pm
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Judson Manning

Joined: 03-14-2005
Location: Atlanta, Georgia USA
Posts: 406

I had a problem with 'sneezing' carbs when I used the double o-ring anti-popping spacer set-up and too rich of jets.  Replacing the o-rings with regular gasketing material was one step in solving my problems the other was ensuring proper atomization to keep droplets of fuel from condensing on the manifold walls.

Looking at your jettings, this is probably the most lean set-up I've seen run on a 907 (which I think is good!).  Most people begin with the Spec 9 (160 main jet) which I find to be ridiculously rich even in a racing application. 

On my 2.2 I'm drifting betwen 135 and 138 mains with 170-190 A/C and 55-58 idle jets and 36mm chokes.  EGT and O2 readings still say I'm running too rich, but that may be a function of the cams I'm running.

The one exception is your pump-jet at 55.  The Spec 9 lists a 60 pump jet while I've had very good luck with 40 and 50 pump jets on my Dellortos.  A 45 pump jet is listed for most applications and is where I'd start.  Too much raw fuel being spewed directly onto a hot intake valve can't be much fun!

You didn't mention what cams were mated to that flowed head and manifold.  It could be the carb-manifold-cam-head-header combination isn't quite optimized.  My first thought is the 38mm chokes could simply be too big for a street 2.0.

Another thought would be a poorly closing intake valve.  After you play with the pump jets and chokes, it might be worth checking to see if the intake valves are properly shimmed.  Worst case, you could have a burned intake valve.