General Category > Quadrajet Carb Talk and Tips
Timing and a lean condition
Cadman-iac:
Question, is it possible to have a lean condition just above idle if your mechanical timing is just beginning to come in at 700 rpm?
After trying 3 different carbs and each one has the same issue, I began to think it might be something else. I pulled the hose off the advance and checked the timing as the speed increased and noticed it started to advance just above idle. I had to stop for the night, so I don't know yet at what rpm it's all in. But could this be possible for the timing coming in too quickly cause a lean condition?
The timing is rock steady at idle and it always returns to the set point immediately, no bouncing around, just quick activation with throttle.
I'll find out tomorrow at what rpm it's all in at.
77cruiser:
I would think otherwise it would do it when you connect the vac. adv. too.
Cadman-iac:
--- Quote from: 77cruiser on November 13, 2025, 07:08:21 PM ---I would think otherwise it would do it when you connect the vac. adv. too.
--- End quote ---
It does, I just unhooked it to check when the mechanical started to kick in. I didn't try to see if it was lean without the vacuum advance on. Might try that tomorrow too.
Cadman-iac:
It's not the timing, does it with or without the vacuum advance connected, and I swapped distributors and it still does it.
One note, this is with the truck in gear, brake applied. Still gotta do a road test with the new distributor.
This distributor has the 5 pin module that will retard the timing by 10° when the 5th wire is grounded. Will have to figure out how I want to use this feature now.
Something else, I posed the question online, twice, and got two opposing views from AI.
I don't put any stock in anything that AI says, because you can ask a question exactly the same 5 different times and get 5 different answers. The best way is to do the testing yourself.
novadude:
Not sure about a lean condition, but in general, I have found that a slow, factory-type curve performs better on stock-ish SBCs. I am not a fan of the "all-in by 2500" approach for mild street engines, as I think those curves generally provide too much timing too soon for a mild engine. They seem to runn better with a slower curve.
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