Join Date: Jun 2009
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I had a very similar problem after running apparently for awhile with a leaky power valve. I'm guessing the carbon buildup had fubar'd the egr valve which got sticky, and wouldn't close every time after acceleration. Led to lean "bog" on acceleration, and crappy idle after a run. Took off the EGR valve cleaned it up good and my problem is gone (actually took a couple tries before it closed reliably). You can test the EGR in your driveway - just put a vacuum on the EGR nipple at idle - as it opens, the engine runs like crap. It's supposed to be open only at speed.
Is the diameter of your new carb the same as your old one (both 1.08?) If you grabbed a 1.21, along with your smaller jets, you'd have a very lean mix I'd guess.
If you found a vacuum leak around the throttle shaft on your old carb, you know how to find them. Make sure there is not some uplugged port sucking in unmetered air on your new carb. I found the other day that I've been driving for a year sucking in unfiltered air from a portal in the air horn.
Mine is a 1978 4.2, MC2100 1.08 with 47 jets and a 5.5 power valve (late opening). Runs like a scalded cat. Now I've just got to get it past emissions.
Last edited by zshooter1; 06-29-2009 at 01:05 PM.