I have a 68 Coupe, 454 BB & TH400. Engine is pretty stock and had a Holley 750 DP and old mech. fuel pump of unknown origin. Over the last 6 months the engine would flood when driving. Fuel would pour out of the carb and "percolate" inside. When it happens, can only drive by keeping revs up when at idle. Changed to 750 Vac.Sec. (better suited to auto I was told) with new needle and seats, adjusted float levels and mixture and fitted a brand new Holley mech. fuel pump rated at 8psi. Problem is still there! It is still flooding! Can anybody suggest what else may be causing this to happen?

Are you using the stock steel fuel line that runs up the front of the engine and across the head intake manifold joint? If so you are probably boiling the fuel as it goes thru that section of line. My old 327 68 would do that on hot days. You would be driving along and all of a sudden the would be a whoosing sound and the engine would shutdown. Fuel had boiled off in the line and subsequently the bowl of the carb, and the car would die. Had to move the line away from the head to keep it from picking up as much heat. Never happened again after that.

Thanks for the reply, but no it has been replaced and is not the old steel fuel line. Have new fuel line and in-line filter.

Still sounds like a heat soak/vapor lock problem. Fuel is picking up heat somewhere along its run to the carb, and then when it goes through the needle valve and the pressure drops it boils. Make sure you have enough air space around the fuel lines and its not up against the block, or near the exhaust anywhere.

Does this happen when just driving along or coming to a hard stop?

It happens with any type of decelleration. If I am cruisng at say 35mph and I need to slow, the moment I take my foot off the gas the car wants to stall. When this happened just yesterday, I had to manually change down the gears when I needed to stop at a stop sign or traffic lights, just so I could keep the revs up, and when I was stationary I had to keep the revs up to keep from stalling. People around me must have thought I was trying to stage at the lights or do a brake burnout!

I had similiar issues with my iron 427 in the summer months only.I installed a splash shield under the performer rpm intake from gmpp and a 1 inch phenolic spacer under the 870 hardcore dp.My intake and carb bowl temps went down and the perculation issue was solved.Hope this helps.

I would say the carb has been messed with inside...butterflys drilled? sec butterflys set right? etc etc.
Are u in Adelade m8?
Heading there 1st week Oct..

I had the same problem...just under harder braking though. If I ran the fuel level to the bottom of the sight (as recommended), under braking fuel would spill over into the carb and stall or almost stall the motor.

Try lowering the rear fuel bowl a tad.

Is it also running rich at idle? One thing you might check for is a float that is sinking or some debris getting stuck in the needle and seat. You can check this by removing each sight plug and seeing if gas pours out. If you do remove a sight plug just make sure to use a container for the gas to flow into! You sure don't want that on a hot motor. Just a thought. I had to change needle and seats twice before to get my car to stop flooding. But gas was comming out of the top of my carb anytime the fuel pump was running.

Thanks for the replies everyone (Steptoe, Perth based mate. Go the Eagles!)

Have stripped carb down this weekend and put back together with all new gaskets, adjusted the mixture, reset the float levels, etc. FYI, the current carb came off of a friends 400SB that never had a problem and ran like clockwork for years. Will replace the fuel pump again tomorrow with another unit, just in case, and will let you know how it goes.

What gets me is the problem was the same before I changed the Carb, Fuel pump & Filter. Could it be coincidence that I have a carb issue or is there something else going on?

Go the Eagles!) Sry m8 we dont have Aussie rules here in NZ
How do u set your float level?
1/heap of rag to catch any fuel
2/remove side plug without engine running to check if too high..if so lower it.
3/Fire engine, adjust level up, at idle till when you shake/bump the side of the car, a very small amount will just spill out