Fuel filter location and air in the fuel.

[tbracker]

I just read that one shouldn't locate a paper element filter on the suction side of a fuel pump as it could ingest paper particles and clog the pump. This just doesn't make sense to me.
I installed a 10 micron filter before my pump to protect it as well as the carb. A filter that creates contamination is an oxymoron.
Recently I've been having a problem with a leak somewhere in the fuel system. The engine will stall on acceleration after sitting at idle for a minute. I looked at the small glass filter I have just before the carb. and it was half full of air and the pressure was down around 3.5 psi. I tightened all the connections on the vacuum side of the pump. Pressure went back to 7.5 but after driving I had the same problem.
Could a filter on the suction side create vapor lock or am I just missing a small leak? I've put 6000 miles on this car before this problem emerged. Time to change the filter element? Could it be heat related?

[392cobra]

The first thing you need to do is take that glass fuel filter off before you burn your car to the ground.

[strictlypersonl]

The first test I'd do is to test the fuel flow into the carburetor. Take the feed hose off and pump into a small container, running the engine for 10 seconds or so. There should be enough fuel in the fuel bowl to do this. With an electric pump, all you have to do is turn the key on. Ten seconds should get you about a quart. If the system is clogged, you'll notice a lot less.

[Ronbo]

40 micron is fine for the input to the pump (as well as a carb). 10 micron is needed only for FI.

As stated, nothing that can crack easily like glass. (or un-screw itself) Throw that glass filter in the trash where it belongs.

[cobred]

Does it stall when you first hit the gas to accell. or as you go through the gears? If on initial accell. I would check the accellerator pump and circuit of the carb.

[tbracker]

The engine usually stutters after 2nd or 3rd gear not on initial pedal application.
I don't suspect anything is wrong with the carb.

[dpmtrspts]

I had a similar problem with my car. It was fine for driving around town, but once I got into 4th or 5th gear on the highway, I couldn't put my foot into it. It took a little trouble shooting, but it turned out to be the electric fuel pump. I only had about 500 or miles on the previous pump. New one is in and it runs great now.

392
Good point about that glass filter. I'll be removing mine tomorrow!

[Night Enforcer]

I would say it is heat related. My son and I experienced the same problem that you are experiencing with our cars. Are you using a different fuel than before? Electric or mechanical fuel pump? I would bet that oxygenated fuel is the culprit. Depending on the altitude and the mix (volitility) of the fuel it can "boil" at 140F or less. The oil lines on our cars run right next to the mechanical fuel pump on their way to the thermostat and cooler. We installed fuel pressure gauges in our cars to see what was happening. We noticed that as the oil temp reached 212F the pressure would drop from 6.5 lbs to 5lbs. When we stopped at a traffic light and begin to pull away at a normal traffic speed and strated to shift to second the pressure would rop to 4 lbs. The engine would sputter and cough for a few yards, the pressure would come back up to 5 and the car would run just OK. Not great but OK. The next stop light would produce the same results. The fuel was "boiling" in the pump or right before it causing it to cavitate and drop the pressure of the fuel going to the carb. In addition it was pumping hot gas to the carb.

We tried wrapping the oil lines, pump and fuel lines with heat insulation and reflective tape. It helped but never really solved the problem. The fuel pressure would still drop. We installed electric fuel pumps and regulators. Problem solved. Pressure stays between 6 and 6.5lbs. Keep in mind that a mechanical pump sucks the fuel toward the pump, thus lowering the pressure on the fuel. Lower pressure means lower boiling point. An electric pump adds pressure to the fuel thus raising the boiling point until the fuel reaches the fuel bowl at which time the pressure drops to atmospheric. Boiling fuel in the float bowl can also cause vapor lock but it doesnt sound like your condition.

Is your fuel tank vented? It needs to be. Some guys I spoke to solved their problem by just venting the tank. You can drill a small hole in your gas cap or cut a small slot in the filler lip being careful not to get any shavings in the tank.

Good Luck

[Anthony]

You need to minimize any restriction, impedence to fuel flow on the suction side of the pump. I'd place the 10um filter on the pressure side of the pump, and if you want a filter on the suction side, they make 40um filters.

[vector1]

read an article where they did an install of either an efi system or carb, they found out the 40 mic filter before the pump would not let enough fuel pass to the pump, recommendation was 100 mic prior to the pump, 40 mic after. fwiw.

this is what i'm running on my efi for about 4 hrs., and no problems yet.

[lineslinger]

Flow restriction on the intake side of the fuel pump.
As stated, sooner or later that glass filter is going to be a bad deal.

[tbracker]

Thanks all. Lots of good info.
Mine is an electric fuel pump about two feet from the tank way in back so I don't think heat is the problem here. Restriction is the most likely problem. I'll bet the pump is cavitating because the filter is too restrictive.
It also occurred to me that the only time I have this issue is when the fuel level is low. The pump is mounted at about the mid level of the fuel tank. So when it has too suck through that filter (which has a years worth of gunk in it), up hill and in warm temps. it's just too much.
The fix is clear. Thanks again.