15 min warm up?

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Nov 27, 2015
Buffalo NY
first I feel it necessary to post a picture of my 3 year old son who LOVES "the 40".

As for the thread - I bought the 40 back in December. I replaced the intake manifold gasket with a remflex due to an obvious leak, replaced the plugs, I rebuilt the carb, removed the smog stuff, set the timing and dwell.

Unless I let it warm up for 15-20 minutes, it runs like complete garbage. By that, I mean it stalls at every significant deceleration, and has backfire out of the tail pipe. If I let it warm up, it runs great - I don't get it. I will admit I am a total novice when it comes to motors. I've done all the work on the truck but it's all learn as I go -

Thoughts? Enough info or no?

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When you had the intake manifold off, did you inspect the inner plenum area below where the carburetor mounts?

They are prone to cracking in that location and could be creating what you are describing.
Lots of pictures in THIS THREAD
Thanks Poser -

Yes that area had a spot which had been previously welded. I got my hands on another intake manifold, however it turned out that had also been welded.

I tested both manifolds using an air compressor and both welds let air through. I took it to a couple shops and neither would re weld the spot.

I talked myself into thinking it wasn't a big deal (mainly because I was anxious to drive it, and said I would address it this winter after I tracked down another intake manifold). My thought process was that even though it was letting a bit of air through the weld, it was just going to a sealed chamber (because of the heat shield/block off plate between the intake and exhaust manifolds).

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