351M bogging under load
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New User
Joined: Sep 2005
Posts: 14
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351M bogging under load
Hi everybody. I bought a '78 f-150 2wd auto 351M. It runs fairly well but has a bad hesitation under load. whether snapped open from idle or floored at highway speed it stumbles and has trouble catching up with itself. It starts well and idles well and will drive at highway speeds. it just stumbles under full acceleration. i will try and list off what i've tried to remedy this problem.
tuneup: plugs, wires, cap, rotor, pickup, reluctor,
rebuilt 2150 carb, accelerator pump is working good
new fuel tank, fuel pump, fuel filters, air filter
i've tried setting the timing anywhere from 8 to 15 degrees
idle air screws were set with vacuum gauge
idle vacuum is sitting close to 20 inches
float seems to be set proper(wet test)
main jets are 57F
when i had the dizzy out i checked the weights and springs, baseplate. Nothing was sticky or jamming. When i add vacuum to the cannister you could see it move. Is it not advancing enough?
would a loose timing chain or skipped chain cause these problems?
What about a rotten egr plate?
It seemed to me like a fuel problem but i've almost eliminated those possibilities.
Any help would be greatly appreciated
tuneup: plugs, wires, cap, rotor, pickup, reluctor,
rebuilt 2150 carb, accelerator pump is working good
new fuel tank, fuel pump, fuel filters, air filter
i've tried setting the timing anywhere from 8 to 15 degrees
idle air screws were set with vacuum gauge
idle vacuum is sitting close to 20 inches
float seems to be set proper(wet test)
main jets are 57F
when i had the dizzy out i checked the weights and springs, baseplate. Nothing was sticky or jamming. When i add vacuum to the cannister you could see it move. Is it not advancing enough?
would a loose timing chain or skipped chain cause these problems?
What about a rotten egr plate?
It seemed to me like a fuel problem but i've almost eliminated those possibilities.
Any help would be greatly appreciated
New User
Joined: Sep 2005
Posts: 9
Likes: 0
You might try adjusting your accelerator pump shot duration. I have had several 351m and I run #60 jets. Works best for me. Also keep in mind if the carb is loading up it can also bog, but usally if this happens it will backfire and black/blue smoke out back. There is a prety good page on this I think its called bubbas m blocks or something close to it. It has a very good area on setting the 2150 carbs. Good Luck
Laughing Gas
Joined: Dec 2000
Posts: 780
Likes: 18
From: East Texas
Here is a link to the web site referred to above.
http://home.earthlink.net/~bubbaf250/
Bubba is a member here, but haven't seen him post in quite some time.
http://home.earthlink.net/~bubbaf250/
Bubba is a member here, but haven't seen him post in quite some time.
