# Fuel delivery issue?



## Chazz (Mar 8, 2010)

Hi guys, first post though I have been lurking for a while now. I'm a novice when it comes to car stuff, but I'm learning as I go along and I'm pretty good with mechanical stuff in general.

Anyway, I'm having an issue with the engine sounding (and performing) like it's starving for fuel when I either cruise at highway speeds for an extended period, or when I hit the accelerator and gun it pretty hard. Before I go on, here are my basic specs:

1967 GTO hardtop
Engine: 1966 421 bored to 428, 670 heads, Summit 2802 cam
Tranny: TH400 3-speed automatic
3:55 gear ratio, 10-bolt posi-track rear end
Holley 800cfm double pumper with manual choke

I have already replaced the fuel pump with a new Carter M4690, and the guy I bought the car from last year said the fuel tank, sending unit, and fuel lines were new.
Now initially, the problem was really terrible. Cruising on the highway for 30 minutes and the car would bog down in spurts that would get worse and worse. Replaced the fuel pump as I stated above, and in the small amount of time I've had off work, I've been testing it out, and I have not encountered the problem to the same degree. I should also note that before I replaced the fuel pump, upon pulling over to see what the heck was going on with the bogging, I could see that the fuel filter canister (located between the pump and carb) was nearly empty, and I had a near-full tank.

A few things I have noticed after installing the new pump:
1. The car starts up great, and the fuel filter canister fills up very rapidly leaving a small quarter-sized bubble. Looks great to me....
2. Driving around at 2500 RPM and under, everything feels fine. Pull over, look under the hood, and the fuel filter canister will be at 3/4 full, trying to fill up (bubbling), but never fills up like it does upon the initial start-up. Seems odd to me...
3. At this point, my idle speed has decreased from 650 to 550-ish, which is getting pretty low and you can tell by the sound of the engine (on the brink of dying). It seems to me that the lower the fuel level in the filter canister, the lower the idle RPM is. If I do a lot of high-rpm driving, when I slow down to make turns and park, I have to close the choke slightly to keep the car from dying.
If I start the car and let it get fully warmed up without driving it, the idle speed is set to 650 RPM. Like I said, this is with a full fuel canister. The idle speed will go down if I drive the car around and park it.

There are no fuel leaks anywhere, and I'm fairly sure the lines are good as they are new (I checked them myself, no signs of aging or cracks). Fuel flows through the lines well enough, and the fuel looks clear (no crap remnants or sediment when I drain the lines). I have already tuned the carb; the float level is fine, mixture is good, and idle speed was set properly on a full filter canister (if that actually matters) and warmed-up engine.

My next order of business would be to replace the fuel filter, but I wanted to make this thread before I started buying more new stuff. Already bought that fuel pump, which seems to help greatly, but does not eliminate the issue.
Sorry for the long winded post, but I'm not sure what information is relevant, so I figured I'd give it all.

Thanks in advance!


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## geeteeohguy (Feb 2, 2008)

Does it bog like it's running out of fuel? It could be an ignition problem, too. You can't go by assumption. I would pull the fuel tank and check the mesh sock on the pick up line. Mine folded in on itself many times over and left me in a bad place for an entire vacation. Check the rubber fuel lines. A lot of times they crack and suck air but don't leak fuel. If they suck air, your pump can't pull enough fuel. You have a different carb, a Holley. What kind of heat spacer do you have? It sounds like your running hot. A lot of '67's were equipped with HD cooling systems. These cars had a fuel vapor return filter in line beween the pump and the carb. The recirculation of fuel, plus giving vapors a place to go helps. Mine runs great since I re-installed it two weeks ago for the first time in 23 years. Never ran better!. You might be getting vapor lock. 670 heads on a 428 = way high compression unless your pistons are dished. What fuel are you running??
Again, I'd pull the tank, check the pickup, check the lines, check the hoses, and go from there. You'll find it.


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## old68goat (Aug 11, 2010)

I had a similiar problem lately with my 68 goat. Turned out to be a hole in the short line from the gas tank to the main line that goes to the fuel pump. Guess it was sucking air but it did not leak any that I could find. Runs great now that I changed that short piece.


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## Chazz (Mar 8, 2010)

geeteeohguy said:


> Does it bog like it's running out of fuel? It could be an ignition problem, too. You can't go by assumption. I would pull the fuel tank and check the mesh sock on the pick up line. Mine folded in on itself many times over and left me in a bad place for an entire vacation. Check the rubber fuel lines. A lot of times they crack and suck air but don't leak fuel. If they suck air, your pump can't pull enough fuel. You have a different carb, a Holley. What kind of heat spacer do you have? It sounds like your running hot. A lot of '67's were equipped with HD cooling systems. These cars had a fuel vapor return filter in line beween the pump and the carb. The recirculation of fuel, plus giving vapors a place to go helps. Mine runs great since I re-installed it two weeks ago for the first time in 23 years. Never ran better!. You might be getting vapor lock. 670 heads on a 428 = way high compression unless your pistons are dished. What fuel are you running??
> Again, I'd pull the tank, check the pickup, check the lines, check the hoses, and go from there. You'll find it.


-The bogging sounds and feels like it's a result of insufficient fuel. As for the heat spacer, I'm not sure what kind it is. Last time I had the carb off, I didn't see any sort of markings on the spacer. However, as for running hot, my engine temperature has never exceeded 200 degrees, so I don't think my engine is overheating.
-I don't think I have that HD cooling line you're talking about, as the only line that connects from the fuel pump to the carb is the fuel line (with the filter). Going to the tank from the fuel pump, I have the fuel line and a vapor return line. Is the 
-I use 91 octane pump gasoline.


So I guess I'll drain the gas tank, drop it and check that mesh sock. Next would be to replace the hose (that stuff is cheap anyway), and while I'm at it I'll blow some compressed air through the lines to make absolutely sure there's no blockages.


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## jetstang (Nov 5, 2008)

Check to make sure the vent on the filler neck isn't clogged, that would restrict flow. We have dirt dobbers that build nests in any hole here, and that little vent is a favorite.


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## BearGFR (Aug 25, 2008)

Howdy...

Do the easy stuff first. Since the new/stronger pump made it better, that's a clue. If you haven't replaced the filter, do that first. A gunked up filter can make it do what it's doing. Next replace all the rubber hoses in case they're sucking air as described. Check the tank vent. If none of that get's it done, then it's time to drop the tank and check out the pickup.

Bear


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## pontiac (Mar 6, 2011)

agreed, you need to look at the pickup. But a 67 gto with factory gas tank setup does not need to drop the tank. pickup can be removed since it is at the front (towards the axle) and there is no interference. of course drain gas level down first otherwise you will be drinking it when you remove the pickup. once pickup is out, also suggest you take a magnetic pickup tool and insert it in the tank to be sure nothing is loose inside that could be up against the pickup sock. have found nuts, bolts, old pieces of hose inside, gas can nozzles, caps, etc. lots of stuff can make its way down inside fuel nozzle.


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## 66tempestGT (Nov 28, 2009)

jetstang said:


> Check to make sure the vent on the filler neck isn't clogged, that would restrict flow. We have dirt dobbers that build nests in any hole here, and that little vent is a favorite.


:agree check this first


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## GTO JUDGE (May 14, 2005)

Dunno if this will cause any issues but.... Using a non vented gas cap when it should be vented? OR Visa-versa?


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## Chazz (Mar 8, 2010)

Well, I replaced all the hose on the fuel/vapor return lines, replaced the in-line filter, and checked the tank sending unit. The mesh sock seemed okay to me, but it did have a crease on one side, folding it about ~45 degrees. I exercised the sock a little bit to even out the crease, so when I put it back it wasn't folded so much. The sock felt like a stiff nylon sort of material, and I wasn't able to straighten out the crease completely, but it's a little better.

Anyway, I also blew some air down the lines to make sure they didn't have any crap in them, and they were both clear. Checked the vent on the filler neck, and no hornet nests or otherwise blocking it . I didn't specifically check the gas cap, although I don't think it is vented. It felt like it's just a stamped metal cap with a gasket.


Going for a test drive afterward, my problem seems to be gone....so far. High-RPM highway driving, there was no bogging or similar issues, and I didn't encounter any bad news on WOT either.

Not sure if it was the hose, or the filter, or the creased sock on the pickup, but I hope the problem is gone now. I'll just have to keep driving and keep an eye and ear on things. Thanks for your help, guys.


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## SWOOSH (Sep 20, 2008)

I tried to start my 68 Lemans that I haven't had very long and it wouldn't start,seemed like no gas. I put a new fuel pump on it and after cranking it a lil bit it started. Now when it sits overnight same thing, acts like no gas. So I got thinking about it and took the gas cap loose and then retightened it. Got inside and fired it right up no pedal at all. Must need a vented cap. It must build up vacuum in the tank. Try changing your cap to a vented one . I am going to change mine.Let me know if this fixes your problem.


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