1956 312 Y block heat riser

Kultulz: No worries on the post.

I just thought some observations of similar symptoms sometimes come in handy.
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Nah, you're OK. It was not directed to you.

That OP has an extremely nice car and if it shot carbon it would embarrass the hell out of me not to mention the cost of gas wasted.

If the mufflers do not have weep holes, maybe consider adding them. I am sure the humidity is worse in FL as compared to CAN.

It might be also that it needs to be taken out on the BIG ROAD and opened up a few times ... ;)
 
Thanks for all the good info guys, I will follow up with the results after I get back to Canada. Just to be clear, this only happens on a cold start and if I razz her a bit it really makes a mess of the garage floor. After the initial blast on start up it seems to go away and the exhaust is certainly clean after warm up. Can someone tell me what's involved in checking that heat pipe? I'm concerned that I'm in for a big job when I get home. Regarding the plugs, as I recall the mechanic said he pulled and re-gapped them. He said they were all in good shape. The guy came highly recommended by several classic car owners as the "go to" mechanic in the area for classic cars.
 
I unwind the spring on mine in the first week as I live SoCal. Next was the intake gaskets with semi blocked crossover. I want intake manifold heat for better atomization but not to boil the gasoline in the bowls; all YBlocks are air gaps and seem to run cooler than most engines I’ve had.. I set the chokes on the first higher rpm just enough to keep it from dying cold. I’ve done that with each carb that’s been on it. With now dual quads I idle on both and set up progressive. Same now for the rear carb. Full pump on cold start only.
When I changed the exhaust manifolds to 57-up I removed the flapper for a spacer. It was the same as the pipe but not the manifold. I used a die grinder to taper the spacer for flow. I have a lot of condensation depending on the weather.

If the choke heat pipe is rotted or broken in the crossover in the manifold trust me you will hear it as an exhaust leak. One of mine in the dual quad manifold I use has Allen set screws for plugs in each end.
 
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