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Gas coming out of bowl vents, new 4100, fuel pump related?

1965GTFB

Member
**Update**************************************
Turns out the problem was the NAPA fuel pump that is spec'd at 4.5-6.5psi was putting out 9.5psi(checked it with my gauge). Added a fuel pressure regulator. One of the keys was putting the carb on my 65 where it did not have the same problem(good excuse to tell the wife that's why we need two Mustangs, for troubleshooting purposes). I also added the small screens that go under the float seats that are probably missing from almost every carb out there, Got them from Mike's Carburetors in Wash. state http://www.carburetor-parts.com/ They seem to have all those little parts(like the screens) that even Pony Carbs did not include in their rebuilds. I probably wouldn't have known about the screens if I hadn't just done the first ever rebuild the 4100 on my 65 a couple months ago and seen them.

All is good with the carb now. See pics of the car in the Car Of The Month topic.

I am working on trying to get NAPA to do some thing about the extra expense to add the regulator and fittings and lines. I don't believe it would have been as simple as "Just warranty it out for another" and roll the dice that the psi will be right without a regulator.
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Firing up the 67 project(289 4V) for the first time to break-in the cam and fuel keeps coming out of the bowl vents after about 20 seconds of running at the 2,000-2,500 rpms needed for the break-in. This is on a complete rebuild every thing(on the whole car) rebuilt or new. Rebuilt the 4100 on my '65 about 2 months ago and it works perfect. This is the 4100 on my son's project we are close to finishing.

- Installed an Autolite 4100 that was still in the box after being restored years ago by Pony Carburetors when they were still in business. Fuel out of the vents.

- Reset the floats way lower twice. Still fuel out of the vents. Primaries first then secondaries.

- Got a rebuild kit and replaced the float seats and needles. Still fuel out of the vents.

- Used the rest of the rebuild kit and went through the entire carb, blew every thing out, got new brass floats to replace the plastic one that Pony Carbs used. Did the dry float set the same way I did on mine. Still fuel out of the vents.

- Reset the floats way low, almost no movement before they close. Still fuel out of the vents.

Starting to wonder if it is the unlikely problem of the fuel pump overpowering the float seats/needles?

Checked the receipt from NAPA for the fuel pump. The number for the one they gave me says it is the HP application. There is another pump that NAPA lists that says "except HP" but oddly it is rated at more Gal Per Hour then the HP version(I'm guessing an error in there online info).

Any chance it could be the fuel pump providing too much pressure or is there some thing related to the floats I'm missing? After each try when I remove the top(air horn) and push the float down fuel squirts out past the float needle so it is holding back at least some pressure.

I might try taking the 4100 off my '65 to try on it but hate to disrupt my perfectly running carb.
 
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