Engine bogging / possible fuel boiling

[73inNH]

"just cruising any speed the engine runs perfectly, but if I decide to get in the pedal it at any speed it will stutter and bog down."

I would think, if the fuel pump wasn't keeping up, then the carburetor would run out of gas at higher rpms. But if I read your post correctly I don't think you're saying that. I think it only bogs down when you punch the gas, right? To me, that's tuning (mixture, accelerator pump etc.)

I have an Edelbrock carb on a 351. I had to increase the size of the accelerator pump jets significantly. I also bought an O2 sensor and dialed in the carburetor. It was way off (too lean) out of the box.

Just a thought . . .

 

[vintageman]

Has the entire fuel line been checked for any kinks. I seem to remember someone earlier last year or so had an engine bogging issue and it turned out to be a kink in the fuel line. A visual inspection of the line would rule that out pretty quick. Good luck.

Tom

 

[MikeJones]

I have an Edelbrock carb on a 351. I had to increase the size of the accelerator pump jets significantly. I also bought an O2 sensor and dialed in the carburetor. It was way off (too lean) out of the box.

Just a thought . . .

@73inNH Thank you for the suggestions. I hadn’t considered the carb adjustments as a possibility

I don’t know if these are related or if I’m chasing several different issues but here’s a overview of what I’m experiencing

1. Engine starts and cruises without any issues until it gets hot then stalls and does not want to restart until it sits awhile. - originally thought vapor lock since fuel lines were sitting on manifold and had been run under heater hoses. I adjusted the carb inlet slightly upward to get the fuel line off the manifold and heater hoses. Also added a fuel filter since there wasn’t one. These changes didn’t improve any issues

2. Engine stutters and bogs down at sudden high rpm. Example: If stopped at a light, I have to ease into the gas, doesn’t like hard launches. Also cruising at any speed and mash the pedal it wants to accelerate but starts running rough and bogs, doesn’t matter if it’s hot or fresh start - seems it wants to accelerate but can’t - originally thought may be ignition coil due to the high rpm symptom but also thought fuel delivery issue.

3. Fuel pressure reading 2.5psi - thinking fuel pump and or blocked line.
4. I believe a local shop did the carb install and tune but not 100% certain of this and you may be right about looking at the carb adjustments

Except for the carb, manifold, plugs and wires, I’m sure most of the fuel and ignition components are original and I have no issues updating them but would like to narrow down the issue(s) before aimlessly throwing money at it.

 

[MikeJones]

Has the entire fuel line been checked for any kinks. I seem to remember someone earlier last year or so had an engine bogging issue and it turned out to be a kink in the fuel line. A visual inspection of the line would rule that out pretty quick. Good luck.

Tom

@vintageman I’m planning to do a full inspection of the fuel lines this weekend. I also plan on disconnecting the line at the tank and pump to see if I can blow some air through and will change out any rubber hose to rule that out.

 

[73inNH]

@vintageman I’m planning to do a full inspection of the fuel lines this weekend. I also plan on disconnecting the line at the tank and pump to see if I can blow some air through and will change out any rubber hose to rule that out.

Remember, too, you could have more than one issue. The stalling when hot might be a different issue than the stumbling when flooring it.

 

[mrgmhale]

There are a few things that will cause a bog on acceleration, and other issues that will cause somewhat related performance issues. If the hesitation is occurring only when the engine has been running a while, and not when it is warming up or recently warmed up, it is possible you are getting some impact from vapor lock - - but not likely as vapor lock tends to cause a more total kind of fuel starvation, not just on acceleration. A weak fuel pump will reduce the volume of fuel being sent into the carburetor fuel bowl, and often will send liquid fuel outside the fuel pump housing, or worse yet, send liquid gasoline into the crankcase 0 which has a horrible impact on the ability of engine oil tp protect the lubricated parts of the engine. It sounds like you are already clued in on the fuel pump side effects - which is good to know. It is possible a low pump pressure or volume (or both) can cause the fuel level inside the fuel bowl to be too low, which will certainly cause a hesitation.

Some other causes include a problem with the accelerator pump system of the carburetor, as mentioned by Mike Jones. Another cause could be someone rebuilt the card or made internal changes to lower the fuel level setting with the fuel bowl float in an effort to increase fuel economy (this was done to our 1973 Mustang 302 2v, causing a slight off idle hesitation. I corrected it when I rebuilt the carb. Other things were also done wrong. Video at the link below, if interested). In some of the video descriptions I include time markers where certain items are discussed, so if you do not feel like watching the entire video you can just Fast Forward to those areas in the video.

https://youtu.be/U-ETjhRqUwQ


An intake manifold leak can contribute to an excessively lean condition that can interfere with the effectiveness of an accelerator pump on acceleration. Another cause is a ruptured or leaking distributor vacuum advance diaphragm, or ported vacuum not making it to the vacuum advance diaphragm. If the ignition timing is not set correctly it can cause a hesitation. Yet another possible cause is an EGR Valve that is opening a little too much or too soon (or both), but I see no evidence of an EGR valve on your Edelbrock intake manifold - so you can rule that out.

One of the things I check for with hesitation problems is if it happens with a cold engine as well as well as when the engine is up to normal temperature. If it occurs mostly at lower RPMs with the throttle being opened, but less noticeable at high speeds where the engine is already running at 2,000 RPM, the problem is most likely related to the carburetor.

In the following links I show how various vacuum systems work, to include showing how to test a distributor Vacuum Advance Diaphragm for leakage. There is a lot of info in these videos, and some overlapping information. Dorry for the overlapping, but once you have learned how these systems work, and how to test them, you will understand far more about your engine and how it is controlled and affected by the various vacuum systems.

https://youtu.be/DtBcK7Lxq1Q

https://youtu.be/sLwXlsHBd4k

https://youtu.be/ohw1oRlcC4c

 

[MikeJones]

There are a few things that will cause a bog on acceleration, and other issues that will cause somewhat related performance issues. If the hesitation is occurring only when the engine has been running a while, and not when it is warming up or recently warmed up, it is possible you are getting some impact from vapor lock - - but not likely as vapor lock tends to cause a more total kind of fuel starvation, not just on acceleration. A weak fuel pump will reduce the volume of fuel being sent into the carburetor fuel bowl, and often will send liquid fuel outside the fuel pump housing, or worse yet, send liquid gasoline into the crankcase 0 which has a horrible impact on the ability of engine oil tp protect the lubricated parts of the engine. It sounds like you are already clued in on the fuel pump side effects - which is good to know. It is possible a low pump pressure or volume (or both) can cause the fuel level inside the fuel bowl to be too low, which will certainly cause a hesitation.

Some other causes include a problem with the accelerator pump system of the carburetor, as mentioned by Mike Jones. Another cause could be someone rebuilt the card or made internal changes to lower the fuel level setting with the fuel bowl float in an effort to increase fuel economy (this was done to our 1973 Mustang 302 2v, causing a slight off idle hesitation. I corrected it when I rebuilt the carb. Other things were also done wrong. Video at the link below, if interested). In some of the video descriptions I include time markers where certain items are discussed, so if you do not feel like watching the entire video you can just Fast Forward to those areas in the video.

https://youtu.be/U-ETjhRqUwQ


An intake manifold leak can contribute to an excessively lean condition that can interfere with the effectiveness of an accelerator pump on acceleration. Another cause is a ruptured or leaking distributor vacuum advance diaphragm, or ported vacuum not making it to the vacuum advance diaphragm. If the ignition timing is not set correctly it can cause a hesitation. Yet another possible cause is an EGR Valve that is opening a little too much or too soon (or both), but I see no evidence of an EGR valve on your Edelbrock intake manifold - so you can rule that out.

One of the things I check for with hesitation problems is if it happens with a cold engine as well as well as when the engine is up to normal temperature. If it occurs mostly at lower RPMs with the throttle being opened, but less noticeable at high speeds where the engine is already running at 2,000 RPM, the problem is most likely related to the carburetor.

In the following links I show how various vacuum systems work, to include showing how to test a distributor Vacuum Advance Diaphragm for leakage. There is a lot of info in these videos, and some overlapping information. Dorry for the overlapping, but once you have learned how these systems work, and how to test them, you will understand far more about your engine and how it is controlled and affected by the various vacuum systems.
https://youtu.be/DtBcK7Lxq1Q

https://youtu.be/sLwXlsHBd4k

https://youtu.be/ohw1oRlcC4c

@mrgmhale Wow! Thank you for the detailed reply and sharing links to these videos which I’ve viewed a couple times since your reply. I find your videos to be very informative and had previously come across your YouTube page (via the search bar in this forum) while looking for topics related to fuel pump and timing,
Due to some work and other obligations, I’m a week or two away from diving back into this and appreciate everyone chiming in to help. All suggestions are greatly appreciated.