Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Big cam, stinky rich idle
77cruiser:
I'm thinking the idle is too lean, try setting idle to max. vacuum, & see how it is. O2 sensors don't work very well at idle with a big cam every misfire reads excess oxygen & reads it as lean.
dave at hsp:
ejowrench, thanks for the reply.
I have not tried ported vacuum. I always set up a big cam engine with full vacuum. Let me tell you why. I try and set the initial at 12 to 16, then run full vacuum and add another 12 to 14, then pull in the centrifugal with another 12 to 14, so I end up with 40 to 42 total at 3500 in the end. I really shoot for the end result as long as I can get my initial good enough to start hot, and the full vacuum at idle so it WILL idle.
I think if I run ported at idle, it will idle even slower because of not enough advance. Make sense?
Dave
dave at hsp:
Marx3, I haven't driven it and watched to see where it's at cruising and wot. The roads have been wet and I really haven't had time. My dad was diagnosed with stage 4 cancer 4 weeks ago, so I've been pretty busy with him.
As far as the sensor mount, I tig welded a bung in the collector on the passenger side, just past the end of the header.
Got my 02 sensor screwed in there. This is the first time I have used the LM-2, so I'm still learning.
I ran the car down the road Sunday with the kid that owns it, but like a dummy, I didn't have the LM-2 plugged in. It runs really good though. Good throttle response and smooth at wot. I hope to get some readings this weekend, if it ever stops raining.
Thanks!
Dave
dave at hsp:
77cruiser, by idle too lean, do you mean the idle tubes? .042 was the biggest long bit I had, so I had my daughter order me more bits up to .050 today. (she is a sales rep for MSC industrial supply) So, once I get those, hopefully Friday, I was gonna go up .002 at a time to see what happens. How big is too big on the air bleeds in the base plate? I'm at .140 now and was gonna go another .002 at a time.
Thanks!
Dave
ejowrench:
Dave, so what you are saying is you set the initial timing at 12degrees, the vac advance at idle adds another 12 degrees, so at idle you have a total of 24 degrees?
When you slowly open the throttle with this set-up, the vacuum drops down, retarding your timing when it should be advancing. On ported vacuum, as soon as you start to open the throttle, the vac advance starts to quickly advance the timing, and then the centrif advance comes on, a nice smooth fast advance curve. Make sense?
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