Author Topic: Fuel problem  (Read 1048 times)

Offline Cheyenne1010

  • Newbie
  • Posts: 38
  • Newbie
Fuel problem
« on: December 17, 2018, 01:31:16 PM »
What's up guys,let me start off by saying that this web site has helped me so much and all the fellow chevy truck owners you guys are the best source to get help when it comes to working on these trucks.
  I have a 1973 C10 long bed 2wd 350 engine with 350 turbo trans.the problem im having just started a few days ago.so from a stop when i accelerate the truck sputters like if its not getting gas,but if i press down on the gas pedal half way to the floor the truck will take off.i changed the fuel filter and i still have the same problem,I've noticed that the fuel filter will sometimes be full with fuel and other times its not.when its full i'll start it up and watch the fuel filter and it'll start to slowly go down then it'll be almost empty spitting out fuel into the filter and if i throttle up the rpm's it just spit's fuel faster into the fuel filter never filling it up.so i turn off the engine and go back to looking at the filter and after 5mins or so i seen the filter fill up.so i change the fuel pump and its still doing the samething.the rubber hose's are brand new with new hose clamps.someone told me its acting like it's sucking in air from somewhere on the fuel line but if thats the case wouldnt it then leak out fuel once i turn off the engine from where ever its sucking in air from?has anyone experience this problem,any and all suggestions will be very much appreciated.
       Thank you fellow chevy guys

Online bd

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 5153
Re: Fuel problem
« Reply #1 on: December 17, 2018, 03:25:52 PM »
Does the engine backfire on acceleration?

The curious problem with glass or transparent plastic fuel filters is that people assume there is a fuel delivery fault based on the observable fuel level inside the filter housing.  Unless the filter and the carburetor are devoid of fuel, the level inside the filter really is irrelevant.  Nonetheless, if you think it's a fuel delivery issue...

Cover some basic checks first:
Try removing the fuel cap to see whether the symptoms disappear.  Recheck the fuel hoses for kinks and deterioration, including those that are less accessible and connecting to the fuel tank(s).  Spray around the carburetor and intake for vacuum leaks - avoid spraying the distributor.  Verify ignition timing and that the timing advances with engine RPM.

Check accelerator pump function:
With the engine off and the air cleaner removed, peer down the carburetor throttle bores using a bright flashlight.  Operate the throttle by hand.  There should be a coordinated squirt of fuel streaming out of the accelerator pump nozzles into each primary bore with every opening of the throttle.  The strength of the streams should be directly proportional to the rate of throttle opening.  If the pump shot just dribbles out of the nozzles, the accelerator pump is worn out or sticking in its bore, the pump check is missing or dislodged by debris, or the fuel level in the bowl is excessively low.  If fuel is emitted by only one of the two nozzles, the nozzle not squirting is plugged.

Measure fuel pump delivery:
Use a proper vacuum/pressure gauge to measure the fuel pump draw (>20" Hg vacuum) and pressure (5-8 PSI) while cranking.  In addition, check the volume of fuel delivered by the pump (~1 qt in 20 seconds of cranking).
Rich
It's difficult to know just how much you don't know, until you know it....
In other words... if people learn by making mistakes, by now I should know just about everything!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Cheyenne1010

  • Newbie
  • Posts: 38
  • Newbie
Re: Fuel problem
« Reply #2 on: December 17, 2018, 05:02:57 PM »
The engine does not backfire,All the fuel lines have been replaced and have new hose clamps.the gas tank has dropped and clean and has a new sending unit and the hose's that connect to the sending unit are good and also have new hose clamps.timing is very good and does advance when throttle is moved.accelerater pump is working fine.all vacuum lines are new and the same with the fuel lines even the hard to get lines are new.the reason im having a hard time diagnosing the problem is that sometimes it'll drive like a champ then i come to a red light,i wait light turns green i step on the gas pedal and it stumbles,i step on the gas pedal a little harder and the accelerator pump shoots fuel in carb and the truck takes off.come to another red light and wait,then i press the gas pedal and everything is good,no stumbling,no hesitation.there are times when it runs fine then times where its stumbles.im going to spary carb cleaner around the intake and the base of the carb,i'll be back with some results

Offline Henry

  • Frequent Member
  • **
  • Posts: 307
Re: Fuel problem
« Reply #3 on: December 18, 2018, 11:12:50 AM »
Hi Cheyenne 1010:
To answer one of your earlier questions, if you have a split in your fuel line that goes between your tank and fuel pump you will not get any fuel leakage out of this...only air in. This is unlike the fuel line between the fuel pump and carb where if you have a break the fuel will come out. Did you say you had inspected and/or replaced the fuel line between the tank and pump?

Your symptoms of accelerating at the traffic intersections really do sound like a accelerator pump starting to go south...they can behave fine when the engine is cold but after driving around a while and getting hot they can start to not work right. If you have made all the checks suggested by others, and you still have the problem, I would suggest a carb tune up including a new accelerator pump. What kind of carb do you have?

Regards,
Henry

Offline Cheyenne1010

  • Newbie
  • Posts: 38
  • Newbie
Re: Fuel problem
« Reply #4 on: December 18, 2018, 04:00:06 PM »
Yes all fuel lines between a fuel pump in the gas tank have been changed changed. The carburetor that I have is a Rochester Quadrajet. And yesterday when I was checking the fuel line by the carb,the filter was empty and all the sudden it filled up with the engine off.

Offline Henry

  • Frequent Member
  • **
  • Posts: 307
Re: Fuel problem
« Reply #5 on: December 20, 2018, 11:40:45 AM »
Hi Cheyenne1010:
I dont think that the filter filling up with fuel after the engine is turned off is necessarily abnormal. If this is one of those little clear plastic cylindrical bodied filters, you are probably seeing the fuel in the hose between the filter and carb inlet coming back into the filter from gravity, and filling it up to capacity. If the diameter of the filter is significantly larger than the hose, I also dont think you should expect to see it filled up to capacity when the engine is running. The "spitting" you see is the normal flow that fills up the diameter area of the hose but is a lot less in area than the filter diameter area...hence it does not fill up. I guess what I am saying here is to not judge the flow rate from your fuel pump just by how full the filter appears when the engine is running. Now, if the filter appears dry when running, that is a problem. I would still perform the fuel pump flow test advised by BD just to rule out the pump as the culprit to your problem. If this 4 bbl Qjet is the original carb to your 73, it is most likely a 4MV and parts are readily available for tune up or repairs.
Regards,
Henry

Offline Cheyenne1010

  • Newbie
  • Posts: 38
  • Newbie
Re: Fuel problem
« Reply #6 on: December 20, 2018, 12:19:37 PM »
Thank you Bd and henry for all your information,im going to have the carb rebuilt and see if anything changes.

Online JohnnyPopper

  • Frequent Member
  • **
  • Posts: 258
  • Newbie
Re: Fuel problem
« Reply #7 on: December 20, 2018, 05:25:02 PM »
More fuel may appear in the filter when the motor is off  because it condenses as it cools.

Sounds like your accelerator pump is sticking and not returning to its correct position at the top of its travel.

See if there is a gap between the pump shaft and the actuator lever.

Rebuild will fix that but if you haven't pulled it yet, I would put carb cleaner right into the main vent while running and goose the accelerator lightly.

Also spray some cleaner around the pump shaft and work it.

That might dissolve what is sticking.