Is this an ignition or carb problem
Thread Starter
Cruising
Joined: Sep 2008
Posts: 13
Likes: 1
From: Bakersfield area More communist than china
Is this an ignition or carb problem
Hey there!
Thanks in advance for any help you can give me.
My 75 coupe has a freshly rebuilt 350 in it (like 10 miles on it) and I'm having problems with it at freeway speeds. When under 50mph it runs strong and has no issues, but the second I hit about 50mph it falls flat on its face, (as in it feels like the engine died completely), but if you slow down to about 45 it picks back up again, or if you stomp it to the floor it'll take a second, then pick up until about 60mph where it stumbles badly.
It has a performer cam, 570cfm Holley street avenger and a Pertronix 'flamethrower' HEI. Timing is set at 11 deg. initial.
Is this an issue with the carb, (I don't have any experience with Holleys), or is it an issue with the distributor? Vacuum advance messed up? Possibly even the fuel pump? The fuel pump is still pretty new, less than 500 miles on it, but I did reuse it (I know, that was stupid). I highly suspect one of these three because they are the only things on the engine that I put back on it that were there before I rebuilt it. It was doing the same thing before the rebuild, but I figured it was the blown head gasket that had something to do with that before.
Thanks for any info you more experienced folks can give me!
Thanks in advance for any help you can give me.
My 75 coupe has a freshly rebuilt 350 in it (like 10 miles on it) and I'm having problems with it at freeway speeds. When under 50mph it runs strong and has no issues, but the second I hit about 50mph it falls flat on its face, (as in it feels like the engine died completely), but if you slow down to about 45 it picks back up again, or if you stomp it to the floor it'll take a second, then pick up until about 60mph where it stumbles badly.
It has a performer cam, 570cfm Holley street avenger and a Pertronix 'flamethrower' HEI. Timing is set at 11 deg. initial.
Is this an issue with the carb, (I don't have any experience with Holleys), or is it an issue with the distributor? Vacuum advance messed up? Possibly even the fuel pump? The fuel pump is still pretty new, less than 500 miles on it, but I did reuse it (I know, that was stupid). I highly suspect one of these three because they are the only things on the engine that I put back on it that were there before I rebuilt it. It was doing the same thing before the rebuild, but I figured it was the blown head gasket that had something to do with that before.
Thanks for any info you more experienced folks can give me!
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
i have the same carb on my 68 mustang. on the mustang forums it is discussed a lot that the 570 street avenger comes very under jetted from the factory. they suggest that you move the rear jets to the front and start with 4 sizes bigger in the back.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Clogged fuel filter or fuel line? Bad gas? Moisture in the dist. cap? Bad plug wire(s)? Vacuum leak (any popping in the exhaust?) Not enough timing? (you have 11 initial which may equate to about 28-30 total,..you likely need 34 or more). Do the advance weights freely move?
Thinking out loud.
Thinking out loud.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Your problem is definitely one of a limited fuel supply. It works fine until more fuel volume is required...then it stumbles. Look for pinched/clogged fuel lines, plugged fuel tank sock, plugged fuel filter, weak or defective fuel pump, and/or carb needle valve/seat problem. It can also be due to carb float being set too low. It does NOT sound like an ignition issue.
Intermediate
Joined: Aug 2008
Posts: 49
Likes: 0
fuel filters
I once had a car that ran great untill the last 20ft on the quarter mile it would run out of gas and when I slowed down it was fine. It turned out it had two fule filters in the line. Got rid of one and that was it.
Hey there!
Thanks in advance for any help you can give me.
My 75 coupe has a freshly rebuilt 350 in it (like 10 miles on it) and I'm having problems with it at freeway speeds. When under 50mph it runs strong and has no issues, but the second I hit about 50mph it falls flat on its face, (as in it feels like the engine died completely), but if you slow down to about 45 it picks back up again, or if you stomp it to the floor it'll take a second, then pick up until about 60mph where it stumbles badly.
It has a performer cam, 570cfm Holley street avenger and a Pertronix 'flamethrower' HEI. Timing is set at 11 deg. initial.
Is this an issue with the carb, (I don't have any experience with Holleys), or is it an issue with the distributor? Vacuum advance messed up? Possibly even the fuel pump? The fuel pump is still pretty new, less than 500 miles on it, but I did reuse it (I know, that was stupid). I highly suspect one of these three because they are the only things on the engine that I put back on it that were there before I rebuilt it. It was doing the same thing before the rebuild, but I figured it was the blown head gasket that had something to do with that before.
Thanks for any info you more experienced folks can give me!
Thanks in advance for any help you can give me.
My 75 coupe has a freshly rebuilt 350 in it (like 10 miles on it) and I'm having problems with it at freeway speeds. When under 50mph it runs strong and has no issues, but the second I hit about 50mph it falls flat on its face, (as in it feels like the engine died completely), but if you slow down to about 45 it picks back up again, or if you stomp it to the floor it'll take a second, then pick up until about 60mph where it stumbles badly.
It has a performer cam, 570cfm Holley street avenger and a Pertronix 'flamethrower' HEI. Timing is set at 11 deg. initial.
Is this an issue with the carb, (I don't have any experience with Holleys), or is it an issue with the distributor? Vacuum advance messed up? Possibly even the fuel pump? The fuel pump is still pretty new, less than 500 miles on it, but I did reuse it (I know, that was stupid). I highly suspect one of these three because they are the only things on the engine that I put back on it that were there before I rebuilt it. It was doing the same thing before the rebuild, but I figured it was the blown head gasket that had something to do with that before.
Thanks for any info you more experienced folks can give me!
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