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Hi all, im sure this is a basic question, but im really lost on a issue im having with my car.
Car is a 76’L, L-48, engine/trans is completely stock
Drives around fine, but under full throttle, once it gets around 55mph it just spits and sputters and falls on its face. Seems like its running out of fuel. Sometimes its better, sometimes its worse but it never runs correctly. Temperature doesnt seem to have an effect
plugs are telling me lean, (whitish appearance)
I have been fighting this issue for almost a year and I just cannot figure out whats broken
entire ignition system is brand new, carb rebuilt 2 years ago, was running fine, all new fuel lines and hoses front to back, new mechanical fuel pump, new fuel filter
I dropped the tank when I did the lines and inspected inside, found nothing visibly wrong, sock was dirty but I could blow through it
my current suspects are either the EVAP system or the tank bladder
Im at a loss. Any input from you guys would be appreciated. Im still learning, and im getting frustrated with the randomness of this issue. Thanks.
Last edited by MGC/D_7601; Feb 28, 2021 at 12:28 AM.
I would pull line to carb and measure pressure and flow while cranking..pressure spec n pic..flow i have to look up..
other than that maybe float stuck or misadjusted? Clogged sock in tank?
if bored https://www.corvetteforum.com/forums...e-on-road.html
Even if the carb is being starved for fuel, it shouldn't run lean (due to an issue NOT internal to the carb). The secondary air valve won't open any farther than the engine rpm (and resulting airflow) will allow. I would think problem is most likely an ignition or timing problem. If you have a points ignition system, the condenser might need replacement OR you may have a poor electrical ground path for the ignition. (Ground for ignition is via the chassis-to-engine block-to-distributor hold down clamp-to distributor housing. If any of the 'contact' points in that run are painted or not 'electrically' clean, poor ground and weak ignition will result.)
I would pull line to carb and measure pressure and flow while cranking..pressure spec n pic..flow i have to look up..
other than that maybe float stuck or misadjusted? Clogged sock in tank?
if bored https://www.corvetteforum.com/forums...e-on-road.html
Ive yet to T- in my gauge, but the sock in my fuel tank is visibly dirty. When I had the gas tank out, I checked it, it seemed to flow ok, but I already ordered another one. once I get the tank back in, ill check the floats, thanks.
Even if the carb is being starved for fuel, it shouldn't run lean (due to an issue NOT internal to the carb). The secondary air valve won't open any farther than the engine rpm (and resulting airflow) will allow. I would think problem is most likely an ignition or timing problem. If you have a points ignition system, the condenser might need replacement OR you may have a poor electrical ground path for the ignition. (Ground for ignition is via the chassis-to-engine block-to-distributor hold down clamp-to distributor housing. If any of the 'contact' points in that run are painted or not 'electrically' clean, poor ground and weak ignition will result.)
I didn't think of this actually, ill have to verify my grounds. my car has HEI ignition and its OEM distributor. New coil, recent cap and rotor. Thanks for the input.
Last edited by MGC/D_7601; Mar 1, 2021 at 03:57 PM.
Dropped the tank, bladder was sitting funny inside the tank, removed the bladder and ill be running the steel tank. Found the evap line on the drivers side of the car broken. new sock coming in this week. New gas cap on the way. New S hose on its way. New fuel filter on its way. Today after repairing the evap line I'm going to check fuel flow rate of the feed line. As suggested while I'm waiting for the sock, ill check the ground integrity of the ignition system. Thanks a bunch for all the help. I've planned a 2 hour highway road trip with the car thinking the new fuel pump I put in in December solved the issue, but it clearly hasn't. I have to figure this out, because it'll never make it on the highway if I cant use the secondaires to merge.
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
I had fuel supply issues after working on the tank in mine once, When putting the tank back in place the supply and return lines crossed causing the supply line to get pinched, took me a while to figure it out.
If you have the fuel vapor canister, your fuel tank does not have a vent and the cap is non-vented. This is because the vapor canister becomes the vent for the tank when it is connected to the system. If you have disconnected the fuel vapor canister, you must put a VENTED cap on your tank or it will develop negative pressure in the tank as the fuel is used.
I fought the same problem for a while and after changing filters, checking the pump, tipple checking the ignition, I tried a can of SeaFoam in desperation.
It started getting better in just a few miles.
I was truly amazed at how well it worked.
On sale right now, $8 at Napa.
If you have the fuel vapor canister, your fuel tank does not have a vent and the cap is non-vented. This is because the vapor canister becomes the vent for the tank when it is connected to the system. If you have disconnected the fuel vapor canister, you must put a VENTED cap on your tank or it will develop negative pressure in the tank as the fuel is used.
This is my current suspicion. I'm completely overhauling the evap system right now.
I fought the same problem for a while and after changing filters, checking the pump, tipple checking the ignition, I tried a can of SeaFoam in desperation.
It started getting better in just a few miles.
I was truly amazed at how well it worked.
On sale right now, $8 at Napa.
Once I get the tank back into the car, I will be 100% sure to run some of this stuff. I've heard a whole bunch of good things about it.
Got the car back together, took it for a nice long ride and opened the secondaries up a few times. No stumbling, no problem, and now I dont smell like gasoline when I get out. Im going to daily it for a few days to make sure nothing comes up but it did good on the test drive. Just as a recap, new evap lines, new charcoal canister, new sending unit, removed tank bladder, new fuel lines, new S hose, new fuel pump, new fuel filter, new gas cap. Based on what I saw, im thinking the evap was the issue. Thank you all again for your help.
Persistent fuel issue
