Gas bubbling?


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By bird55 - 12 Years Ago
(Todd, I read somewhere that the new Edelbrock 94's are supposed to correct the bleed down problem. Not to sure about that plus the gas boiling after shutting off the engine is another problem. My bird has no room left for a phenolic spacer to insulate the carbs unless I want to cut holes in the hood. I used chrome stainless steel lines from Vintage Speed with absolutely no leakage. I had to modify the lines that Charlie sent me to clear the linkage so I feel comfortable bending up new ones. It wasn't as hard as I expected. I am using the stock tach drive 57 distributor with Petronix and MSD 6 but it needs to be gone through. At this point I have the vacuum advance plugged and bumped up the initial enough that the mechanical advance gets me to the right total advance. Still need to work on that. Thought about coming to some of the events over your way but not ready to push the Bird over Hecker and Pacheco Pass yet. It is a fairly strenuous drive from Santa Cruz.)



OK, my bird's gas line filter always seem to bubble or percolate after I drive a bit. I've always taking it as normal? Is it a problem, carb leaking down or venting issue. The filter is the original style glass AC unit, so it's easy to see. Something I need to fix?
By gekko13 - 12 Years Ago
The basic problem is the fuel blend.  Virtually all pump gas now days is formulated for closed system EFI.  There is little or no consideration given to "vintage" (pre-2000) engines.  About all you can do is look for 100% gasoline (non ethanol) and insulate your fuel lines as best you can.  You could also experiment with shielding the carburetors from the intake and blocking off the heat riser passage.  I have used a sheet metal spacer between the carb and manifold that extended under the float bowls to deflect heat off of the manifold itself (on my single 4 bbl intake).  It also may act as a heat sink to conduct some heat away from the carb base.  Unfortunately, those early birds were notorious for high under hood temperatures too which only exacerbates the problem. 
By suede57ford - 12 Years Ago
I havr the fuel boil problemwith my teapoton the black supercharged sedan on hot days as well.   It our fuels.  Really hard to correct, even with insulators.

See you this weekend Al.

By The Master Cylinder - 12 Years Ago
suede57ford (6/14/2012)
I havr the fuel boil problemwith my teapoton the black supercharged sedan on hot days as well. It our fuels. Really hard to correct, even with insulators.




That's because they are blending lighter ends (pentanes, NC5's) in the gasoline these days. On warmer days the lighter ends vaporize because they boil at a lower temperature than gasoline. This "bubbling" you witness in your fuel filter is the Pentanes boiling out of the gasoline.
By PF Arcand - 12 Years Ago
Alan: Just a thought. Don't know how close your stainless lines are to exhaust manifolds & other heat sources. But, stainless steel conducts heat much faster than regular steel...
By bird55 - 12 Years Ago
thanks for the replies. I didn't ever think it might have been the fuel.

As Paul suggests, I don't have stainless fuel lines, just steel, but they are somewhat close to the engine block and header. But then it rises up and out towards the rad. to get airflow when running. Course all this occurs after I shut it off.

I'm probably going to ignore it and keep driving and enjoying it! Tongue