I just swapped the stock 2v carb, cast intake, and valley pan in to replace my my 4v carb, aluminum intake, and felpro gaskets with exhaust crossover blockoff. I idled the truck long enough to get the carb tuned and it died. My clear fuel filter showed bubbles. I'm guessing the intake is so hot that it is boiling gas in the carb or fuel line. I have a 1/4 in rubber-ish spacer installed, but not the stock spacer. Never had the stock spacer.

So my question is how did the stock setup avoid this? Was the stock spacer cooled by coolant? Was it a PCV spaced and the airflow was enough? My manifold gets HOTTT without the exhaust crossover blocked!

 

Bubbles usually means you have an leak in the line somewhere.

 

The bubbles are in the pressureized side, so a leak there would be obvious and bubbleless... (is that a word? Oh well.)
I suppose there could be a vacuum side leak, but no problems before the carb swap...
Also it continues after the truck has died, and only when hot.

 

Any other suggestions?

 

They used to use heat riser valves to close off one exhaust outlet so all the exhaust would flow thgrough the crossover. When the motor got warm the valve would open, and most of the exhaust would go out the pipe and less through the crossover.

I suspect that you have something blocking one exhaust outlet, and all of the exhaust is flowing through the crossover and through the other pipe.

Do you have one or two exhaust pipes?
Is there exhaust out both sides?
Do you have a heat riser?
Does it open?

I haven't worked on a stock motor in a long time, so I'm not sure what should be there.

 

No, no heat riser installed. Stock manifolds with true dual exhaust.

 

Do both exhaust pipes have the same pressure at the outlet?

 

Put a spacer under the carb, and re-routed the fuel line to a cooler area. Helped some. Was able to drive, but still had heat related issues.

The manifold is so hot that if you hit the throttle lever after running(engine off), the gas boils and vents back out above the carb as a white cloud. I guess I'm going to do another exhaust crossover blockoff gasket set. I know it worked last time.

 

What is the engine temperature when this happens?

 

180-185F(normal operating temp) and about 75F outside temp.

 

A lean mixture will cause high exhaust temps.

Do the exhaust pipes glow after running? You should check them in the dark.

 

Emissions-tester guy I know told me to use a wooden carb spacer when I go to put a 4V carb on my truck (81 F350 400M) as wood doesn't conduct heat real well, thereby preventing the problem you're experiencing.

Specifically, he suggested an Edelbrock EDL-8725, $24.95 from Summit Racing:

http://store.summitracing.com/partde...5&autoview=sku

Did a search on Summit's site for Edelbrock carb spacers, seems Summit has only the 4V variant. But you get the idea....

-chris