At wit's end, bad accelerator pump?
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Postmaster
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From: O-O-O-Oreilly's
At wit's end, bad accelerator pump?
I just can't seem to put this to bed. My truck will only run half decent with a radically re curved dizzy (very little spring tension). Otherwise it stumbles and coughs though the carb during acceleration. I think I have ruled out all ignition related stuff, all of it is new. My accelerator pump seems to work, but the stream of fuel seems a little weak and not solid. I have tried adjusting it to no avail. The carb is adjusted to pull max vacuum. It seems like it just leans out so much under acceleration that it coughs. Also, when cruising, if I rapidly floor it, there is a very noticeable bog before it picks up again. Any thoughts guys? Thanks in advance.
Laughing Gas
Joined: May 2006
Posts: 1,140
Likes: 13
From: Port Orchard Wa
Hmm....
What is your total mechanical advance?
Are you running ported or manifold vacuum?
Have you tried using vacuum to verify initial timing?
Have you checked the setting on the air valve?
What do your plugs look like (are you running too lean?)
What is your total mechanical advance?
Are you running ported or manifold vacuum?
Have you tried using vacuum to verify initial timing?
Have you checked the setting on the air valve?
What do your plugs look like (are you running too lean?)
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Postmaster
Joined: Nov 2015
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From: O-O-O-Oreilly's
Seeing as my harmonic balancer has slipped, hard to see total advance, but I did limit it a tiny bit, so it is likely around 20 degrees. The issue persists with both ported and manifold vacuum.
I am not sure how to use vacuum to verify timing, and tips?
What is the air valve? Are you referring to the vacuum advance unit?
I will check the plugs today.
Thanks for the reply!
I am not sure how to use vacuum to verify timing, and tips?
What is the air valve? Are you referring to the vacuum advance unit?
I will check the plugs today.
Thanks for the reply!
Laughing Gas
Joined: May 2006
Posts: 1,140
Likes: 13
From: Port Orchard Wa
The possibility of slippage in the harmonic balancer is why I asked about setting initial advance with vacuum gauge. Basically you hook up a vacuum gauge and set initial (total) timing for max vacuum and then back off just a bit. More info here....
Either way, total mechanical advance is the difference between initial and when it's all in at around 3000 rpm. This should not be affected by any balancer slip. Too much could cause you to run lean. I asked because of your statement about recurved dizzy. 20 seems ok. Might even be a little low.
The air valve is what determines when your secondaries kick in. It can be adjusted - could be related to bog when cruising. Check out the info on your specific carb.
Finally, this subject can be contentious, but use manifold vacuum (unless your drag racing).
Either way, total mechanical advance is the difference between initial and when it's all in at around 3000 rpm. This should not be affected by any balancer slip. Too much could cause you to run lean. I asked because of your statement about recurved dizzy. 20 seems ok. Might even be a little low.
The air valve is what determines when your secondaries kick in. It can be adjusted - could be related to bog when cruising. Check out the info on your specific carb.
Finally, this subject can be contentious, but use manifold vacuum (unless your drag racing).
Senior User
Joined: Jan 2016
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From: Central Kentucky
Have you rebuilt the carb? I would do that before I did anything else if it hasn't been done already.
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From: Simi Valley, CA
I just can't seem to put this to bed. My truck will only run half decent with a radically re curved dizzy (very little spring tension). Otherwise it stumbles and coughs though the carb during acceleration. I think I have ruled out all ignition related stuff, all of it is new. My accelerator pump seems to work, but the stream of fuel seems a little weak and not solid. I have tried adjusting it to no avail. The carb is adjusted to pull max vacuum. It seems like it just leans out so much under acceleration that it coughs. Also, when cruising, if I rapidly floor it, there is a very noticeable bog before it picks up again. Any thoughts guys? Thanks in advance.
D4AZ-9A586-A (replaced C2AZ-9A586-B) .. 2100 Series Auto-Lite/Motorcraft 2V Carburetor Kit (Motorcraft CT-499-D) / Available from Ford & auto parts stores.
Applications: 1962/74 Passenger Cars/Trucks, 1966/74 Broncos & 1969/74 Econolines.
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Postmaster
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From: O-O-O-Oreilly's
Thank you all for the info. It should be noted that the problem only recurred when I went back to a stock distributor curve. I am also running manifold vacuum. I should have stated it, though it is in my signature, but my truck has an Edelbrock 650, rather than the Motorcraft 2100 series carb. I am looking to take it apart and clean it today.
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