Carb severe flooding problem
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
Carb severe flooding problem
I thought I had finally fixed the last problem on my 68 convert with NOM 454. The QFT 750 cfm dbl pumper carb would not maintain proper fuel level in the fuel bowls- overflowed to the point of the carb filling up with liquid gas. I backed off on the fuel pressure with a smaller electric fuel pump/regulator and changed the needle, seat and power valve, but did not change the two floats. The car maintained proper fuel level (glass sight ports) for about twenty minutes idling in my garage and ran perfectly on my ten mile test drive, them abruptly died and would not re-start in the parking lot of the local Target store. Opening the hood I found the fuel pressure was zero, since the carb was filled up with liquid gas- apparently from the needle/seat being wide open.
When I inspected the floats when I previously worked on the carb they appeared OK. No sloshing of fuel in the brass primary float and none in the nitrophyl secondary float. I'm going to replace both now. Question- could a pinhole leak on the brass float open enough when the engine heat increased to make it leak and sink the float? If so, why was there no gas in it when I previously checked it?
When I inspected the floats when I previously worked on the carb they appeared OK. No sloshing of fuel in the brass primary float and none in the nitrophyl secondary float. I'm going to replace both now. Question- could a pinhole leak on the brass float open enough when the engine heat increased to make it leak and sink the float? If so, why was there no gas in it when I previously checked it?
Melting Slicks
Joined: Feb 2006
Posts: 3,105
Likes: 96
From: Sunrise FL
I fought your problem for quite a while on my 750 DP Holley...of which I think your QFT is similar. Changed both floats to brass (from nitrophyl), problem solved!
The nitrophyl would absorb fuel WHEN HOT after driving...and sink
The nitrophyl would absorb fuel WHEN HOT after driving...and sink
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
floats
hmmmmmmmm. QFT is, as you comment, interchangeable with Holley. I ordered two nitrophyl floats filled with closed foam from QFT since they claimed they would not leak and absorb gas like a leaky brass float would do. I'm still puzzled why the original floats did not slosh or feel heavy when I checked them. I have previously found bad brass floats and they always had enough liquid in them to detect a sloshing when you checked them.
I believe your comment about them leaking when hot makes sense, but where does the gas go when they cool off? RA
Le Mans Master
Joined: May 2006
Posts: 5,814
Likes: 414
From: Pittsburgh suburbs Pa.
When I read something like this I see pictures of burned out corvette shells. Please work on it outside of your garage until you are sure it is right . Hope you get it fixed soon .
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
fire hazard
When this problem first happened a couple weeks ago, the car was IN the garage. Fortunately I got everything electrical turned off and pushed the car outside. I have three fire extinguishers in the garage, but car fires are hard to put out. I saw a Vette catch fire many years ago and it was burned to a crisp before the fire department arrived.
