Technical Running too rich issue...

ok kids, so my intake is the original updraft intake. I fabbed a "u" pipe from it and mounted a downdraft carb. She runs pretty good for the most part. The problem I am having is that she runs rich after she heats up. From what I figured, the cause of this is that the fuel is atomizing, then turning back into fuel and pooling in the "u" pipe, thus, making her run rich after, say, 15 minutes. I tapped into the exhaust manifold and plumbed 1/4" copper tubing to the "u" pipe and coiled it around to keep the pipe warm (it gets ice cold and sweats like a pig), BUT, the cold kicks the heat right out of the park! My second thought is to maybe tap into the coolant lines and see if that helps warm the pipe up.
The key, I believe, is to get the "u" pipe warm on a constant basis, as it doesn't run rich until the pipe gets cold and sweats. But this seems to be challenging. Any ideas out there??

 

I suspect the people that know the answer will want pictures.

 

Lighter pressure step up springs if it is AFB type or smaller number power valve if Holley. Just an idea that works in conventional V8s

 

What carburetor are you using, do you know the cfm rating?

 

Its an older 2bbl gm carb, all i know at the moment

 

Sorry, 1bbl....fat fingers!

 

The carb is too big and thats why its overly rich. That engine probably made 25hp? and that carb came from a 'modern' 4cyl making 80?hp - just a guess but you get the idea. I'd try to find an old zenith, one with the smallest throttle blade - match it to your updraft carbs blade - and you might be in business.

 

Lol close, 125hp. The confusion lies with the fact that it runs perfect until the pipe gets cold. Not rich at all until that point.

 

How much exhaust is going through the copper pipe?

 

Apparently not enough! Its 1/4" tubing.

 

Believe the issue may be caused by an "intake manifold" which is way too long.

Back in the pre-fuel pump days (even pre-vacuum pump days) some manifolds had to be long (although less long than yours) to accomodate gravity feed. To prevent the icing issue, the entire intake manifold was exhaust jacketed. That is, the entire exhaust flowed in a double pipe around the intake manifold. And they STILL had icing issues.

Not sure you will solve this one with that manifold.

Why not a good updraft??? Or, if you must have a downdraft, turn the original intake upside down and place the carb directly on the intake.

Jon.

 

The intake cannot be flipped, it's not symetrical. I may have to go updraft if tapping into the cooling system doesn't work out. In all reality, I just don't like the updraft carbs...sounds silly, I know, but I have been trying to avoid it from the beginning of the project! Thanks for your input btw.

 

introducing warmed air into the carb throat might be helpful