Fuel system problem?

[Sinister]

I'm having a bit of a problem with my '69 LWB, 350 with a Quadrajet. When I'm on the freeway my truck gets to about 50mph and starts sputtering until I back off the pedal. Fuel pump looks fairly recent. I'm thinking this is fuel problem, but I might throw in a fresh set of points, rotor and cap, and see if that helps...

[cduster]

i would check the fuel filters

[Sinister]

Thanks for the quick reply, but I already did that...

[Alex Hayley]

Have you checked the condition of your lines(both hard and soft lines)? I recently pulled my tank and cleaned it as well as replaced all soft lines and cleaned the hard lines. This maintenance made a difference.

[GBWatts]

If the truck sits for long periods (like over the winter here in Michigan) the gaskets in the carb can dry out and shrink/distort a little which can cause fuel draw problems. I know this is a problem with the cork type gaskets in a Holley carb, it might be a Quad issue as well. You sound like when you hit 50 MPH you start having a fuel starve problem which this would cause so you might want to look at that.

[cdowns]

did you check the filter sock inside the gastank?? have you tried taking off the gascap to see if that solves the problem??

[Sinister]

Thanks for all the replies. I'll check the filter sock, haven't tried taking off the gas cap. The carb could probaly use a rebuild. Hardlines seem ok, I just replaced
the softline going from the gastank to the hardline to the fuelpump. Is there supposed to be a fuel filter there?

[Alex Hayley]

The only filter between the tank and the pump is the sock in the tank. In addition to replacing the softlines I also blew out the hardlines and pumped about a gallon of new gas through the entire system and let it come out of the inlet pipe at the carb.

Did you replace the cap lately? Cdowns has a good idea. If you have the problem again, just reach back and remove the gas cap. See if the engine smooths out.

[Sinister]

Originally Posted by Alex Hayley

The only filter between the tank and the pump is the sock in the tank. In addition to replacing the softlines I also blew out the hardlines and pumped about a gallon of new gas through the entire system and let it come out of the inlet pipe at the carb.

Did you replace the cap lately? Cdowns has a good idea. If you have the problem again, just reach back and remove the gas cap. See if the engine smooths out.

I did replace the cap recently. PO's of this truck and the '72 i used to have had fuel filters between the tank and pump, strange. I'll check the sock and try taking out the filter...

[68gmsee]

Before you start removing the seat and tank sending unit, check the fuel flow to the carb.

Disconnect the coil wire to the distributor so the truck doesn't start and remove the line again going to the carb. Have someone crank the engine while you direct the flow into a container. Use extreme caution since you will be dealing with gasoline squirting out.

Insure that you are getting adequate flow. I had one that was just barely shooting gas out. Leaking diaphragm inside the fuel pump.

The other problem I had on another truck was an extremely restricted fuel line along the frame from the tank to the fuel pump.

[Eddie47]

Originally Posted by Sinister

I'm having a bit of a problem with my '69 LWB, 350 with a Quadrajet. When I'm on the freeway my truck gets to about 50mph and starts sputtering until I back off the pedal. Fuel pump looks fairly recent. I'm thinking this is fuel problem, but I might throw in a fresh set of points, rotor and cap, and see if that helps...

Had same problem. Found one bad Plug Wire, new set of wires and runs prefect.

[Sinister]

Well, I just took it out for a spin without the gascap, still the same. It seems to be sputtering/missing? and occasionally backfiring at around 50 mph. It might just be an ignition problem...

[68gmsee]

Sinister, check all of the obvious as mentioned. Timing, spark plugs and wires, rotor and cap, leaking vacuum advance, fuel flow, wires inside the distributor, etc...

If all of these looks good, then you may be looking at the carb itself or maybe even the engine. If it's old and worn it may be trying to tell you something. Bad timing chain, worn cam, etc...

[screamin_c10]

I know this sounds stupid, but is the fuel filter in correctly? I have seen them in backwards and it will flow fuel, just not ENOUGH to maintain higher rpms under load. This in turn causes the truck to starve for fuel and start dropping out at speed.

[Sinister]

Aaaaargh!!! I went ahead and swapped out sparkplugs, points, rotor, cap.
Didn't want to start. Swapped back to the old points, just to see, still didn't want to go. I think I put all the wires back correctly when I changed the cap. I think now would be a good time to put in the HEI I got in the garage, start from scratch...