57ford 292 with holley 4v and ford dura spark ign, similar issues,turned out to be to lean,put larger  jets in primaries. problem cured. prev replaced durs module and coll,no cure ,richer primaries cured the issue.

Check your balancer if its original for possible slippage, not uncommon. And your distributor isn't pre 1957 by chance?.. If so, it won't work properly with that later Summit  carb..


Paul

What  a bout a  vapor lock That would cause  the problem your talking about, and  highway driving  is prime time for it to happen!

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You might check and see what your total available Advance is. Initial + Vacuum+ Centrifugal. You should be aiming for around 44 total. What do the Plug Insulators look like color wise?. 

  

I think the 46's are probably fine but it does sound like you have a tuning problem.


Lawrenceville, GA

also it would backfire through the exhaust when I step on it. i may have a timing issue

.\Thanks Charlie, so do you think then that the 46es are better for what i have? I do have plenty of fuel pressure.

Leaning out is not plugs.  Since you have tried two carbs, and assuming they were reasonably well tuned, you probably have an ignition or fuel supply problem.  If you did not spend time tuning, then you need to.

I think the 45s probably are not necessary for your build since it sounds pretty well stock with a few bolt-ons.  Gap will be the same, about .032 for stock ignition, possibly wider for electronic ignition.



Lawrenceville, GA

Anyone have any input here or have this same experience. Since my build 292, bored .030, pertronix 2, header, mumert intake, summit 600 carb, original 4 speed T98...
My engine builder installed autolite 46, after about 6 months i put in 45s as it seemed to be the preference for some longer highway driving. Which I do from time to time but not often. Somehow my engine seems to lean out and stop pulling around 2800 rpm. I have checked timing, trid different carbs. Something is up and I am not sure what. I am thinking I might put the 46s back in. what is the best gap for the 46s? Thanks folks.