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Diagnose part throttle issue

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Trevor Jessie

Trevor Jessie

Yoda
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I think I may have asked this before, but here it is again.

Everything runs pretty well when I accelerate or cruise ... unless I transition to part throttle (slight accel) from cruise. Then the car goes lean and starts missing. Punch the accelerator down and the problem goes away. Initially I thought the problem was too light of oil in the dashpots. I switched to gear oil and the problem lessened, but it is still there. This is a basically stock 1275 with twin SU's ABC needles. The ignition is standard, and the problem occurs with or without the vacuum advance. The timing seems stable. (I actually tried an alternate distributor.)

In my mind this is a carb issue, but what am I missing? The car has no emission equipment and there are no detectable vacuum leaks.

Any suggestions?
 
That was my thinking, but with a basically stock engine I can not see why I'd need drastically different needles.
 
I don't remember, I'll have to check.
 
Plugs are gapped at 0.025
I don't suspect a coil/plug problem since it accelerates fine at WOT. But at this point I'm entertaining all ideas.
 
I found some AAZ needles I don't think they've been modified. They seem to be working a bit better. Truthfully, the engine is so worn out it is amazing that it pulls itself at all. I should probably leave well enough alone.
 
Worn out motors will give you fits with pretty near anything.
 
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