Thread: Sbc bogging at around 40 mph and above

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Unfortunately, like most of us, I believe he changed the fuel filter after he started having problems instead of when he installed the new carb.

Also, check for a vacuum leak, a vacuum leak can cause this type of problem too (vac gauge will tell you). The choke will compensate for the increased air until the choke opens, at which point the metering rods won’t operate correctly because of the low vacuum.

And, if you have an automatic transmission check the vacuum line connection at the transmission to see if it has come off or burned against the exhaust (often overlooked).

Originally Posted by 36 sedan

Unfortunately, like most of us, I believe he changed the fuel filter after he started having problems instead of when he installed the new carb.

Also, check for a vacuum leak, a vacuum leak can cause this type of problem too (vac gauge will tell you). The choke will compensate for the increased air until the choke opens, at which point the metering rods won’t operate correctly because of the low vacuum.

And, if you have an automatic transmission check the vacuum line connection at the transmission to see if it has come off or burned against the exhaust (often overlooked).

All good thoughts. At this point the most important thing to me is for Treygan to reply about his symptoms, and especially if it's accelerating OK on initial start. Without that I'd just be guessing.

On the fuel filter, if it had a decent in-line filter in place and he changed it out and still has the symptoms I don't see how he would have got crap in the carb unless the filter ruptured, and I've never seen that happen in all my years. Your idea about vacuum affecting metering rod action is a great point, and I had never really considered that possibility. Hopefully Treygan will get on-line and give us a few more clues!

Sorry guys. I worked last night so I just woke up. So to try to answer your questions. Up to this point it has ran fine until I get up to 190 degrees. I can drive 75 mph no problem. And I changed the fuel filter the day I changed the carb which was about a month ago. I was looking at it at a little bit though and found that the spacer for the air cleaner, which had been painted orange at some point, had some paint peeling and bubbling on the inside of it. So I know it could have easily come off and gone right into the carb. As for the ignition it's just the old style distributor. And the plugs when I changed them didn't look bad to me. They had a tan color to them, some worse than others. I hope I did ok answering. I'm not a great mechanic and probably not even a good one. I am taking the carb with me tonight to work and my boss who has do e it before is going to help me open up the carb and take a look. Thanks guys for the help and the welcome. And I'll post pics as soon as I get some extra time. Thanks again and keep it comin.

Originally Posted by Treygan

Sorry guys. I worked last night so I just woke up. So to try to answer your questions. Up to this point it has ran fine until I get up to 190 degrees. I can drive 75 mph no problem. And I changed the fuel filter the day I changed the carb which was about a month ago. I was looking at it at a little bit though and found that the spacer for the air cleaner, which had been painted orange at some point, had some paint peeling and bubbling on the inside of it. So I know it could have easily come off and gone right into the carb. As for the ignition it's just the old style distributor. And the plugs when I changed them didn't look bad to me. They had a tan color to them, some worse than others. I hope I did ok answering. I'm not a great mechanic and probably not even a good one. I am taking the carb with me tonight to work and my boss who has do e it before is going to help me open up the carb and take a look. Thanks guys for the help and the welcome. And I'll post pics as soon as I get some extra time. Thanks again and keep it comin.

The passages that you'd plug on the carb are on the fuel (liquid) side, not the air going through the venturi, IMO. You say "...old style distributor." Is it an HEI type like this with the coil on top?

HEI.jpg

Your plugs being "tan color" is ideal. Says your mixture is good. I'm thinking you've got an ignition module breaking down when it heats up. Just need to know exactly what kind of distributor/ignition you have.