Fuel filter question

Fuel filter question


Senior Jeeper
1979 Jeep CJ5 with '72 304 V8, MC2100carb,T150 trans, AMC20 rear diff with locker, Dana 30 front diff, Dana 20 Tr Case, Procomp Springs, Gabriel Ultra shocks.
The PO cut and plugged a couple lines in the fuel system that I am assuming were part of the charcoal canister in the engine compartment as well as the rollover and check valves in the rear wheel well. I do have what appears to be a fuel filter on either side of the fuel pump. One is located where the charcoal cannister would have been and the other is on top of the engine. I'm wondering if I need both filters. One of my problems is that I have some leaks and it is affecting my acceleration as it sucks air. I figured I could remove one of the filters and that would reduce the number of potential leaks. Which one should I remove? I did wonder if the one before the fuel pump was acting as a check valve so fuel wasn't being pulled back in to the tank.
Your problem could be no fuel tank venting, this can be checked by removing the gas cap after a drive and hearing air rush in. If there is no venting, a vacumn will occur in the tank as fuel gets pumped out, this has an effect on the pump operation. The tank is usually vented thru the charcoal cannister. I have had fuel filters fore and aft of the pump with no problems as it cleans the fuel before the pump. The venting system should be on a diagram in a repair manual. Another pumping problem can occur when the rubber fuel line out of the tank develops cracks as it ages.
Thanks. This is a relatively recent problem and have noticed some minor fuel leaks around the filter fittings. The rubber hose is clearly in bad condition and the hose clamps don't seem to be doing their job, so I believe that replacing the hoses will resolve the problem. I'm just wondering if I need a filter on either side of the fuel pump.
Fuel filter before the pump is extra. You don't "NEED" it, but unless you're actually starving the carb of fuel, it's not hurting anything and can stop gunk / dirt buildups in the pump causing failure.

The one by the engine stops gunk from going into the carb, obviously... But it is between the pump and carb for a reason i believe. The pump has a harder time "sucking" fuel from tank through a filter and into the pump, than pushing the shorter distance from pump through the filter and into the carb.

You "can" run them both, but I am not convinced it's "needed" though neither am i convinced the "set-up" is your whole problem.

I think it's (as said above, and you seem to think too) a mixture of the hose sucking air, and the filters being dirty.

I like the glass filter on top of the engine, so I can see the filter condition at a glance.

Some do not like these filters though.

If its the stock mechanical fuel pump, I would buy enough new fuel line to go from the tank to the pump, and temp (or permanently) leave out the 1st filter.

You may find Torxhead is right as well however about the venting. I've heard it quite a few times. There are a few ways to make sure there is a vent for the tank though, and you can cross that bridge when you are satisfied the rest of the fuel system is correct and not leaking...

~ Jr
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Thanks guys. I'm going to replace the bad lines and take the filter before the pump out. There is no vacuum being created when I remove the cap. I think its just the bad connections. I guess I'll find out after I replace them. I do have the charcoal canister but I don't have the rollover or check valve that goes in the rear well, so I'm not sure if I'd benefit from doing a partial assembly of that system.
The way I see it, the purpose of the rollover valve is just as it is titled. if you rollover, lay it on its side, or go down a steep hill, gas will fill the vent line and fill up the float bowl in the valve and close it off. Otherwise, the gas will run out through the charcoal cannister on to the ground. The check valve is just a backup system after the rollover valve. Anyway it does sound like your rubber lines need replacing, hopefully it will solve your problem. The ones coming out of the sending unit are the worst to replace.
Don’t forget that the fuel filter, installed after the pump, needs to have the double outlet for the return fuel line to prevent vapor lock. The return line on the filter needs to be positioned up, above the main line that feeds the carb in order to work properly. This diagram doesn’t show it but the return line attaches to an extra nipple on the sending unit at the tank.

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