78 Vette
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
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From: Inver Grove Minnesota
78 Vette
I'm having some problems under heavy acceleration. It seems to "studder". This mostly happens off the line not once your already moving. I think it is in the carb. It is a holly not sure what model. I already replaced the plugs and wires hoping to solve the problem but to no avail. It has the L-48 with an hei distributor and about 35,000 miles on it.
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
Could be lots of things. Here are a few that come to my mind.
1) carb accelerate pump*
2) carb float
3) fuel pump
4) fuel filter*
5) clogged tank sock
6) floating valves
* are the ones that I'd check first
1) carb accelerate pump*
2) carb float
3) fuel pump
4) fuel filter*
5) clogged tank sock
6) floating valves
* are the ones that I'd check first
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
The pump is internal to the carb. Here's a link that might help:
http://www.chevyhiperformance.com/howto/45798/
http://www.chevyhiperformance.com/howto/45798/
Safety Car
Joined: Sep 2005
Posts: 4,057
Likes: 99
From: Southeast, Tennessee
St. Jude Donor '09 thru '26
just a guess, but looking at your picture, is it possible that your fuel line (it appears to have a bend crimp in it from the reverse angle it is forced to make to bolt up) might be restricting fuel flow?? it might be sufficient under no load situations, but might not deliver enough fuel under load.
i can't tell from your picture, but if the fuel line is resting on the block or intake manifold, or is close to the exhaust in being routed from the pump to the carb, it could be percolating a bit and not delivering pure fuel to the carb (percolation would cause airation of the fuel to a great extent and alter the air/fuel mixture by adding excessive air through the carb delivered by the fuel in addition to the carb suction). this also would be much more evident under load if it wasn't all that severe.
just a couple of other suggestions.
i can't tell from your picture, but if the fuel line is resting on the block or intake manifold, or is close to the exhaust in being routed from the pump to the carb, it could be percolating a bit and not delivering pure fuel to the carb (percolation would cause airation of the fuel to a great extent and alter the air/fuel mixture by adding excessive air through the carb delivered by the fuel in addition to the carb suction). this also would be much more evident under load if it wasn't all that severe.
just a couple of other suggestions.
Last edited by srs244; Mar 30, 2006 at 03:55 PM.
Le Mans Master
Joined: Aug 2000
Posts: 6,362
Likes: 7
From: Brazos TX
Cruise-In IV Veteran
Cruise-In V Veteran
I agree with the other suggestions. One other thought, for the photo it looks like the choke is closed down too much. You may want to adjust that as well.
As for the accelerator pump, does the studder happen when you jab the throttle? Like it hesitates a little? Or does it happen once you have your foot all the way in it and it's slow to accelerate while it's popping?
As for the accelerator pump, does the studder happen when you jab the throttle? Like it hesitates a little? Or does it happen once you have your foot all the way in it and it's slow to accelerate while it's popping?
Instructor
Joined: Jun 2005
Posts: 248
Likes: 1
From: Apopka Florida
Originally Posted by srs244
just a guess, but looking at your picture, is it possible that your fuel line (it appears to have a bend crimp in it from the reverse angle it is forced to make to bolt up) might be restricting fuel flow?? it might be sufficient under no load situations, but might not deliver enough fuel under load.
i can't tell from your picture, but if the fuel line is resting on the block or intake manifold, or is close to the exhaust in being routed from the pump to the carb, it could be percolating a bit and not delivering pure fuel to the carb (percolation would cause airation of the fuel to a great extent and alter the air/fuel mixture by adding excessive air through the carb delivered by the fuel in addition to the carb suction). this also would be much more evident under load if it wasn't all that severe.
just a couple of other suggestions.
i can't tell from your picture, but if the fuel line is resting on the block or intake manifold, or is close to the exhaust in being routed from the pump to the carb, it could be percolating a bit and not delivering pure fuel to the carb (percolation would cause airation of the fuel to a great extent and alter the air/fuel mixture by adding excessive air through the carb delivered by the fuel in addition to the carb suction). this also would be much more evident under load if it wasn't all that severe.
just a couple of other suggestions.
That looks like a pretty bad crimp in the hose. Try fixing that first. Good luck
Burning Brakes
Joined: Jul 2004
Posts: 1,235
Likes: 0
From: Sick of these TOOLS & AZZHATS in DC
also check the rest of yor fuel line, especially the short piece of hose that connects the fuel tank to the hard lines running forward....it may be cracked/deteriorated allowing your fuel pump to suck air too. Don't ask me how I know this....I have just gone through a 2 week ordeal with my '78 that was exhibiting the same probs you're having. It drove me nuts 
You'll have to drop your tank to check this, so while you have it out, it's a perfect opportunity to check and clean the tank inside and that pick-up "sock".
You'll have to drop your tank to check this, so while you have it out, it's a perfect opportunity to check and clean the tank inside and that pick-up "sock".
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Racer
Joined: Oct 2005
Posts: 343
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From: Rye TX
Originally Posted by srs244
just a guess, but looking at your picture, is it possible that your fuel line (it appears to have a bend crimp in it from the reverse angle it is forced to make to bolt up) might be restricting fuel flow?? it might be sufficient under no load situations, but might not deliver enough fuel under load.
i can't tell from your picture, but if the fuel line is resting on the block or intake manifold, or is close to the exhaust in being routed from the pump to the carb, it could be percolating a bit and not delivering pure fuel to the carb (percolation would cause airation of the fuel to a great extent and alter the air/fuel mixture by adding excessive air through the carb delivered by the fuel in addition to the carb suction). this also would be much more evident under load if it wasn't all that severe.
just a couple of other suggestions.
i can't tell from your picture, but if the fuel line is resting on the block or intake manifold, or is close to the exhaust in being routed from the pump to the carb, it could be percolating a bit and not delivering pure fuel to the carb (percolation would cause airation of the fuel to a great extent and alter the air/fuel mixture by adding excessive air through the carb delivered by the fuel in addition to the carb suction). this also would be much more evident under load if it wasn't all that severe.
just a couple of other suggestions.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
It wasn't the bend in the line it was just an illusion in the picture it wasn't kinked much it is just because the line covers are bigger than the fuel line inside. I was thinking that it may need to be tuned were would be a good place to start?
Last edited by JustinD; Apr 1, 2006 at 01:59 PM.