Fuel Starvation
Thread Starter
Navigator
Joined: Jan 2013
Posts: 9
Likes: 3
Fuel Starvation
Needing a little advice. I have been fighting what seems to be a fuel starvation problem with my 77. I have changed the rubber fuel lines, front and rear, fuel pump, and even changed the sock in the tank but still having the same problem. Car cranks and runs fine until ran for a little while. After pulling the fuel tank I noticed the tank has a rubber liner. Inside the rubber feels good and no sand or grit is in the tank, could the rubber liner be sucking up on the pickup sock and starving off the fuel? This is the first rubber tank I have ever seen. I have been dealing with this for a year and I am stumped.
Pro
Joined: Jan 2010
Posts: 518
Likes: 12
From: Panhandle
You have done the right things so far.
No insult intended, but have you checked:
1. Fuel filter in the carb, If Quadrajet?
2. External Fuel filter
More than once I've had problems with filters. Had one external filter and it looked pristine. I didn't give it a 2nd thought. After going the long route of checking other things, came back to the filter and bypassed it and sure enough. It was the problem.
Had one fuel filter that ran ok when engine was cold; after a while would die. Cooled down ok, then died!
In your case, I would replace BOTH filters to be safe.
The other thing is to do fuel capacity test. See if the fuel pump is pushing the designed amount of fuel.
Another thing to check is to make sure both the fuel and vent lines are not blocked.
Good Luck
No insult intended, but have you checked:
1. Fuel filter in the carb, If Quadrajet?
2. External Fuel filter
More than once I've had problems with filters. Had one external filter and it looked pristine. I didn't give it a 2nd thought. After going the long route of checking other things, came back to the filter and bypassed it and sure enough. It was the problem.
Had one fuel filter that ran ok when engine was cold; after a while would die. Cooled down ok, then died!
In your case, I would replace BOTH filters to be safe.
The other thing is to do fuel capacity test. See if the fuel pump is pushing the designed amount of fuel.
Another thing to check is to make sure both the fuel and vent lines are not blocked.
Good Luck
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Have you recently changed out the "S" hose at the fuel pump? Many folks change that out with regular, straight hose and curve it as needed. They then find that there is a 'fuel starvation' problem. Regular hose kinks at the turns and shuts off fuel flow. That "S" hose should be of the molded variety; most Corvette aftermarket suppliers sell them.
If you have changed or rebuilt the carb recently, that is another area of concern. (don't think you have, as you didn't mention it)
If you have changed or rebuilt the carb recently, that is another area of concern. (don't think you have, as you didn't mention it)
Thread Starter
Navigator
Joined: Jan 2013
Posts: 9
Likes: 3
Thanks for all the feed back. I replaced the "s" hose but with straight fuel line (have ordered the corect "s" line). Have replaced the carb and the fuel pump and still the same problem. What leads me to think it is a fuel starvation problem is that it runs fine when cold and the fuel filter is 90% full. After running a little the fuel filter is only 1/8 full and car runs real lean (ie. black smoke from exhaust). Once warm I have to hold the pedal to the floor to start, when cold starts with only a pump of the accelerator and a few rotations of the engine. Once started, but still cold, cranks with only a turn of the key with no touching the pedal. And once again I have to hold the pedal to the floor when warm.....Will get back once the "s" hose comes in and installed to see if that fixes it.
Pro
Joined: Jan 2010
Posts: 518
Likes: 12
From: Panhandle
To me it is starting to sound like a carb problem.
If you have to push the pedal to the floor to start it when its warm, you have a flooded Carb and you are unloading the carb. Pushing air to dilute a rich mixture.
To verify this theory, check a few spark plugs. If they are black/soothy. You don't have starvation. If they look nice and clean. Keep looking...
If you have to push the pedal to the floor to start it when its warm, you have a flooded Carb and you are unloading the carb. Pushing air to dilute a rich mixture.
To verify this theory, check a few spark plugs. If they are black/soothy. You don't have starvation. If they look nice and clean. Keep looking...
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
Thanks for all the feed back. I replaced the "s" hose but with straight fuel line (have ordered the corect "s" line). Have replaced the carb and the fuel pump and still the same problem. What leads me to think it is a fuel starvation problem is that it runs fine when cold and the fuel filter is 90% full. After running a little the fuel filter is only 1/8 full and car runs real lean (ie. black smoke from exhaust). Once warm I have to hold the pedal to the floor to start, when cold starts with only a pump of the accelerator and a few rotations of the engine. Once started, but still cold, cranks with only a turn of the key with no touching the pedal. And once again I have to hold the pedal to the floor when warm.....Will get back once the "s" hose comes in and installed to see if that fixes it.
WHAT KIND OF CARB..i.e. HOLLEY, Quadrajet, etc????
Was the fuel pump the same as the factory...where you have 3 ports on it. 2 for the rubber "S" hoses and one for the steel line to the carb that requires that special 90 degree 3/8" female flare fitting????
GM did not have an exposed fuel filter. The fuel filter is in the Quadrajet. What type of set-up do you have????
BLACK SMOKE IS RICH FUEL CONDITION.
****FACE SHIELD OR SAFETY GLASSES REQUIRED****
After running the engine shut it OFF and look down inside the carb CAREFULLY and see if you have fuel dripping onto the throttle plates....you can also PEAK into the carb when running VERY CAREFULLY and see if you have fuel dripping when it is running. This may be a simple float adjustment...depending on what carb you have.
If it drips when shut off...remove your fuel cap and test again and see if it stops. If it does.....more than likely your vapor return line is plugged to your charcoal canister and emissions hoses have been deleted or damages and the fuel tank is pressurizing itself.
DUB
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Le Mans Master
Joined: Oct 2006
Posts: 8,940
Likes: 35
From: El Cajon California
Consider this scenario cause it happened to me.
The heat riser was stuck closed, the heat riser redirects the hot exhaust gas from the passenger side exhaust thru the intake manifold existing out the passenger side exhaust. This is done to quicken the warm up time of the engine.
When stuck the intake heats up, as the engine warms the intake gets too hot and the fuel percolates in the carb and causes fuel starvation.
The heat riser was stuck closed, the heat riser redirects the hot exhaust gas from the passenger side exhaust thru the intake manifold existing out the passenger side exhaust. This is done to quicken the warm up time of the engine.
When stuck the intake heats up, as the engine warms the intake gets too hot and the fuel percolates in the carb and causes fuel starvation.
Thread Starter
Navigator
Joined: Jan 2013
Posts: 9
Likes: 3
Well again have had the problem for over a year. So wanted to drive it but got to where the motor started a slight deep knock, since I have pulled and replaced the motor installing the same carb (Quad) and new fuel pump and still the same problem. So I started with changing the fuel lines and sock, still same problem. Thinking it was the carb switched to an Edelbrock carb and Edelbrock fuel pump (to match fuel preasure) and still the same problem. Also I have looked in the carb and no fuel dripping onto throttle plates. Will pull plugs today and check. And thanks again guys for all the feedback.
Thread Starter
Navigator
Joined: Jan 2013
Posts: 9
Likes: 3
its a 1977 (close ratio 4-speed L-82) and I have replaced the motor with a 383 Stroker and DUI dist. Still having Same problems as with the original motor. So don't think its that, but thanks for your feedback.
Pro
Joined: Jan 2010
Posts: 518
Likes: 12
From: Panhandle
Bob
More Ideas!
http://www.onallcylinders.com/2012/0...carb-problems/
http://www.hotrodders.com/forum/edel...ch-190918.html
Then, go back too the basics!
Check the plugs. If sooty, take them all out and check/clean and set the gap.
If you have a compression tester...wouldn't hurt to do the test. Would just rule out a couple engine possibilities.
Set the timing and adjust the carb.
You gotta know what the engine vacuum is. Buy/borrow a gauge? Check and record that. Like the article says...if vacuum is very low..plays havoc on the carb.
PCV valve: check for suction and rattle
If it rattles, its not stuck.
You said you checked the fuel and vent lines. How did you ensure the vent line was not blocked? Just need to close this item out.
Cheers for now.
More Ideas!
http://www.onallcylinders.com/2012/0...carb-problems/
http://www.hotrodders.com/forum/edel...ch-190918.html
Then, go back too the basics!
Check the plugs. If sooty, take them all out and check/clean and set the gap.
If you have a compression tester...wouldn't hurt to do the test. Would just rule out a couple engine possibilities.
Set the timing and adjust the carb.
You gotta know what the engine vacuum is. Buy/borrow a gauge? Check and record that. Like the article says...if vacuum is very low..plays havoc on the carb.
PCV valve: check for suction and rattle
If it rattles, its not stuck.You said you checked the fuel and vent lines. How did you ensure the vent line was not blocked? Just need to close this item out.
Cheers for now.