Welcome to Cadillac Forums @PCG01
I'll redirect your query to the appropriate subforum discussion- what model '65 Cadillac are you working on?

 

How long is vehicle sitting before you notice this problem?

 

I'm guessing you know you have a good pump. I would start looking for a tiny pin hole in the fuel line.

 

Is the carb insulator missing and its boiling out from heat soak?

 

No(t sure what the carb insulator is?

 

its a plastic compound spacer 1/2 -3/4 inch that stops heat transfer from the intake to the carb - you could have googled it? run your car good, let it sit and take the carb bowl covers off - gas inside? should be some in it....

 

Thanks
Will try this weekend

 

Sounds more like a weak fuel pump to me or possibly a pin hole in the line from the tank

 

I have a 1965 deville 429 with low fuel bowl if it sits and I have to prime the carb several times to start it. Weak fuel pump, leaky line somewhere, carb valve leak?..

 

Merged with your existing thread on the same topic.
Please allow a single thread to work for you.

 

Probably leaky well plugs in the carburetor. Very common.

 

Somebody will have to do some testing on it. Somebody will have to see how hard it is to pull fuel through the fuel line from the gas tank. If it is hard to pull fuel from the gas tank then it probably isn't the fuel pump. If fuel flows easily, then somebody should test the fuel pressure to determine how close to spec it is.