New mechanical fuel pump - now flooding?
 

Had my fuel pump give out on me while doing a freeway run last month and replaced it with a parts store Airtex unit. A quick drive around the neighborhood seemed to indicate all was well.

Yesterday I ran some errands yesterday and it almost stalled almost every time I came to a stop. After a quick stop at the store I fired it up and it immediately stalled out. I took a peek under the hood and noticed the top of the carb was soaked in fuel. The car was facing a little bit down hill so I pushed to the other side of the lot where it was facing uphill figuring I could lower the float level a little bit. I was able to get it started but not without smoking out the entire supermarket parking lot. There was what appeared to be raw fuel on the tailpipes when I got home. You could clearly smell it.

All the plugs are soot black. I disassembled the carb and nothing looked extra out of order other than the accelerator pump looking a little tired. I'm going to go ahead and rebuild it since I have it apart.

Flooding has never been a problem. Is it possible this new pump is putting out too much pressure?

What make carb ?

Jim

If you are running a Quadrajet I am sure they don't like high fuel pressure (~4psi max).
Best bet it to put a temporary in line fuel gauge and see what you have.
Either ways I'd bet your have too fuel pressure.

Could be a foreign object was keeping the needle off the seat so the fuel was just pouring in. Too much pressure is always possible but it would have been flooding from the beginning. I run an Airtex and have zero issues with pressure.

The 1972 Pontiac Service Manual says you should have anywhere between 3 and 6.5PSI for fuel pressure running the Q-Jet.

'68 Q-Jet rebuilt to one of Cliff's mild recipes in his book about 6 years ago.

I thought it might be junk in there too since the last pump let go but I didn't see anything out of the ordinary. I figured I'd tear it down and clean it really good anyway.

Maybe I'll see about picking up a reasonable fuel pressure gauge this week.

I'm looking at Airtex's website and for the '68 GTO with a 400 it has the pump rated at 5.25-6PSI pressure so this should not be a problem unless there is a defect. The large canister like I use on my '72 is rated between 6.5-9PSI and I don't have any issues. As far as not seeing any blockage it doesn't take much. If you are cleaning it you should also check that the needle is seating completely. There is a procedure in Cliff's book if you have it. If not I can type it up for you.

Lot of the current chevy and ford pumps are coming thru with the wrong springs per several of my buddies (at work) with those cars. Say the idle fuel pressure with a gage on the line is 7-8 psi. Check the fuel pressure with an accurate gage.

Most of the "fixes" have been installing a fuel pressure regulator before the carb.

One guy tried 3 different pumps with the same result.

Tom Vaught

+2 on too much fuel pressure. The 1967-68 carburetors still used the early float/hinge pin design, and they do not like a lot of fuel pressure. These early carburetors are pretty much limited to 6psi with a .135" fuel inlet seat and large stock float in them.....Cliff

Any older sections of rubber hose that you may have on the out bound side of the pump to the carb sould get replaced with new hose rated for use with the new gas these days.
one.003" item of crap from the old hose will have the carb flooding out and old hose can do that at any time, most times when your 100 miles or more away from home on Sunday night in the rain!!!

I'm running a factory metal fuel line from the pump to the carb so putting in an inline gauge or regulator is a little bit of a hassle without rigging some new lines and fittings.

Is there a particular brand of fuel pump that tends to be better than others? A new pump is less expensive than a pressure gauge so I may just gamble and order one along with a carb kit from Cliff and see where it takes me.

Buy another fuel pump.
Bought a napa one last year and the Qjet started flooding,
I figured dirt in the carb. rebuilt it, still flooded, took the carb apart again still flooded, bought a fuel pressure gauge and it would build to 12 lbs.
Got another pump, no more problems.
Hope this helps.

Just ordered a Carter M4690 from RockAuto for about $30. Had good luck with their stuff in the past, we'll see if it helps.

I had the exact same thing happen when I trusted an auto parts cheapie fuel pump. Pump was putting out way too much pressure. I went to the GM dealer and got a new AC Delco for a 69 GTO the one with the return line and no problems since.

Had a couple inquiries as to how this has been going. Between work and home projects I haven't had a lot of time to devote to the car lately.

The good news is I painstakingly refreshed my carb with one of Cliff's HP kits. The only thing I found that was obviously wrong was a missing check ball by the accelerator pump. I put the carb together last time so I'm the only one to blame for that.

Finally got around to pulling the Carter pump out of the package this afternoon. It appears to be the exact same unit as the Airtex so I'm not sure it will solve my problem.

The Airtex pump is stamped 40607 5112 while the Carter pump is stamped 40607 4812. Aside from the last 4 digits, every other stamping is identical. Guess I'll still install it and see how it goes. RockAuto doesn't list a Delco pump for '68, but they do for '69. However, all the other pump part numbers (Airtex/Carter etc) are different for '69. Is there any reason they would be different?

http://forums.maxperformanceinc.com/...1&d=1384738761

http://forums.maxperformanceinc.com/...1&d=1384738873

http://forums.maxperformanceinc.com/...1&d=1384738888

The one pump has a return fuel provision so I would suspect that drove the part number change. All of the pumps are the same basic housing configuration. The lever arm construction and the pump spring typically set the pressure. Some of the old Carter Pumps had the "6-Valve" main bodies.

Tom Vaught

Tom Vaught

Look closely. Both those pumps have returns.

Obviously I need new Computer Glasses!

There it was right in front of me. LOL!

That being said I retract the PN change being due to the Fuel Return provision.

Tom Vaught

Pontiac Fuel Pumps
 

Perhaps you have the incorrect Fuel Pump.

This is a photo of the different Pontiac Fuel Pumps.

The pumps with the larger canister are generally for cars with A/C. The difference in the larger canister ones to is the way the feeds point, the way they point is weather it's an A , F,G or X body & the others are for the B&C body cars.