See thru gas filter and mechanical fuel pump

35 coupe

35 coupe

Senior Member
I just installed a new offy fuel pump on my 35 (all stock) and a see thru gas filter. On initial start up the filter filled with gas and after about 1-2 minutes run time, the gas in the filter trickled down to where it looked like a heart pumping fuel at idle. revving the engine it picks back up but does not fill the filter. I did not take it for a ride to see how it runs, but wondering if anybody else seen this. I changed the pump, because when I hit high second gear it sounds like the pump I had could not keep up, plus the fuel would bleed back over night. THANKS...
 
Is there a way you can adjust the pump so as to increase the pressure? I don't recall what an OFFY fuel pump looks like.
 
You want to increase pressure install a stronger spring under the diafram, Never heard of a OFFIE fuel pump. Why dont you try a genni 36 mech.one thats has been rebuilt. Early and late are 2 diff pumps. Both will work on 35-36. or use a glass bowl one from a 47-48 will also work. ken ct. With a paper filter in it. Sorry theres only 1 pump correct for 35 Small domed one. Dome diam is 2" inside the top cover lip. NOT 2 1/4".
 
35 Coupe, Offie ? I'm with Ken.

On "trickle down", if you mean the filter began losing the visible level of gas it had, and was replaced with air, then that air had to come from someplace, meaning you are sucking air into your system from a fitting or gasket before the pressure side of your pump. What is an "Offie" fuel pump?
 
I have those filters on two vehicles: just before the fuel pump on a 36 pickup, and between the pump and carb on my truck. In both cases the fuel only fills the filter about 1/3 of the way. Both vehicles have standard mechanical fuel pumps.

I think a mostly empty inline plastic fuel filter is normal.

Tom
 
Offenhauser brand fuel pump, from speedway. there is only three fittings before the pump. the one on the tank, and the female and male on the rubber hose into the pump, and none of them leak any fuel.
 
47COE said:
I have those filters on two vehicles: just before the fuel pump on a 36 pickup, and between the pump and carb on my truck. In both cases the fuel only fills the filter about 1/3 of the way. Both vehicles have standard mechanical fuel pumps.

I think a mostly empty inline plastic fuel filter is normal.

Tom
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I, likewise, have never seen a see-through filter full of gas but they all carry enough to keep the engine running. Don't have them on my car but all the ones on my motorcycles and lawn tractors never fill up.
 
I had to lengthen the push rod on the old 21 stud in my 33. I pulled the rod apart (the ends were pressed in) and added some washers until it worked well.

Make sure you don't overdo it. too long and you will bend something.

Mart.
 
I dont think you have a fuel pump problem. The glass bowl pumps do not fill the entire bowl with fuel, if the bowl fills and the engine starts and continues to run at idle and under hand throttle acceleration then its working fine.

If you have an issue that the engine is stumbling or skipping at higher rpms under load then it would suggest its more of an ignition issue than a lack of fuel issue. Unless you have an air leak in the input line, the fuel willl not run back in the tank. The fuel output pressure needed is no more than 2-3 lbs so it doesnot come out in a pee stream and a new pump does not require stiffer or heavier spring and longer push rods that all bunk.

Most people are having pump issues because they seldom use their cars and the fuel pump diaphram deteriorates because it is held in a expanded stationary position for too long a period of time, the diaphram stretches and the efficency decreases. I have posted before if you are experiencing a hard start issue it is more likely the new fuels evaporating out of the carb than a deficency with the fuel pump due to occasional use.
Since you are trying to eliminate a stumble problem and have replaced the fuel pump the next step is to check for carb air leaks and then check the timing settings and the vacuum brake.
 
ken ct said:
You normally dont lose fuel through a leak,you suck air through it when the engine is running. ken ct.
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Ken, that's the key point that many times is misunderstood. Having a negative pressure, there will be no sign of gas leaking out, but air is being sucked into the system.
 
Probebly just another pump made in China brought in to the usa by Offie, i wouldn't have too much confidence in it.ken ct OMO
 
If you have the glass "see through" filter make sure it is in a location where it can't strike metal and fracture. I've seen two vehicle fires that were started because of those glass filters.
 
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