General Category > Quadrajet Carb Talk and Tips
off idle stumble/lean mixture
Cliff Ruggles:
It's no secret I'm not a big fan of those camshafts. Went down that road when they first came out, and once again not that long ago, and both times very disappointed in the results.
Aside from the Thumpa and Mutha-Thumpa super tight LSA grinds, I get more complaints in here about XE cams than any other.
I know it's not good news, and doesn't help the situation, but hopefully with careful tuning you can get past the negative traits thrown into this deal by the XE camshaft.......Cliff
forkitman:
This is all a hobby, a labor of love. Sometimes I think I need a different hobby,LOL. Thanks again for your advice.
I will keep you updated . Bob
jwilson645:
--- Quote from: Cliff Ruggles on August 29, 2016, 05:32:36 PM ---M series metering rods are correct.
We NEVER read plugs to determine rich/lean, impossible with this new fuel.
We tune for results, smooth off idle, and at light heavy throttle, thru transition, etc.
RPMS have NOTHING to do with the movement of the power valve, it moves with throttle angle/engine load, which you can not duplicate without actually driving the vehicle.
A stronger spring lowers the cut-in point, but seldom the correct course of action to tune for light part throttle issues. The PP spring is for tuning heavy part throttle and quick movements of the throttle which require increased fuel delivery. The accl pump also helps these scenarios.
For light/part throttle operation and light load tuning do it with the APT system. I prefer to determine the correct jet size FIRST, by doing some heavy part throttle driving, then go back and fine tune the part throttle/light load range with the APT.
If you can't come in range and the jet size is fine, they go with smaller metering rods (assuming too lean). If it's rich, go with larger metering rods.
The camshaft you are using is not a user-friendly cam. It may be contributing or even causing the low rpm issues. I've had a number of engines in here with multiple issues, and the XE cams have been a common denominator more times than not.
The are on 110LSA, with short seat timing events and excessive opening/closing velocity for the valves. "Chop" or irregular engine operation below 2000rpms is not uncommon with them, and is caused by the early intake closing point, combined with the short seat timing/quick valve events (bouncing the valves on the seats and some noticeable "reversion").
This certainly produces a nice sounding idle, if you like a little "lope", but I've seen those engine run rough up thru and past 1500rpm's or so until things would smooth out, with the only real contributor being the camshaft.....FWIW.....Cliff
--- End quote ---
Cliff, is there any particular brand cam that you recommend? I have the XE cam also and am having a helluva time getting my carb dialed in. I know that isn't the only issue but I don't really like the way my truck idles with it anyway. It's a 350, bored .040 with stock 99 Vortec heads and stock exhaust manifolds.
Cliff Ruggles:
What is the compression ratio and which XE cam are you using?.....Cliff
77cruiser:
What's the timing initial & mechanical curve setup? Any mods done to the carb?
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