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Author Topic:   running lean
Dirt Full Roller

Total posts: 39
posted July 31, 2003 11:35 AM  
I have a Q-jet I have no vac lines hooked up is this why it is running lean if so what is the one or ones that need to be hooked up thanks

Dirt Forum Champ
Total posts: 1019
posted July 31, 2003 11:51 AM  
As long as the ports where those vacuum lines were hooked up are now blocked off, this won't be a cause for the carb to be lean.
What causes the quadrajet to be lean in many cases is the fuel feed tubes sometimes will fall out of the top of the carb and into their fuel wells and fuel cannot then be picked up and delivered when the secondaries open.
Remove the top of the carb and on the underside of the top of the carb there should be 4 brass tubes. Sometimes one or both of the outer ones can fall out and be sitting in the fuel well below.
Another cause for a lean condition could be a jammed power piston. It is the aparatus that holds the primary metering rods. Once you remove the carb top, it'll be the "thingy" that is sticking thru the center of the gasket from below (not the accelerator pump piston that is off on the LF corner of the carb).

There's a number of other things that can cause the condition as well, such as secondary air flaps that don't open, or even a mismatched internal gasket that allows a vacuum leak.
But these are some things to check anyway....

Hope that helps,

[This message has been edited by KPLugnut (edited July 31, 2003).]

Dirt Freak

Total posts: 402
posted July 31, 2003 01:18 PM  
dont forget the size of the secondary metering rods. What was the carb off of originally? Obviously some are set up to deliver more fuel than others. The carb on my 355 right now came off of a 71 455 olds. only took minor tweeking ot run. I had one off of an 86 4.3 chevy that i stripped for parts. the secondary rods had almost no taper to them.

Dirt Full Roller

Total posts: 39
posted July 31, 2003 03:31 PM  
it is out of a 76 chevy blazer

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