carb problem?
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carb problem?
ok, when i got my 76 f100, i knew NOTHING about how engines work or any of the parts on them, but recently ive been learning alot, but i hae no idea about stuff like this. When i pull out in my truck, it feels great, but if i all the sudden slam onthe gas, it just kinda boggs down and feels like it has no power. the engine is a 390 4bbl, but the guy i bought it from put an autolite 2bbl carb on it and a 2" carb spacer. does it just need a bigger carb or is there some other problem?
thanks!
thanks!
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
ok, when i got my 76 f100, i knew NOTHING about how engines work or any of the parts on them, but recently ive been learning alot, but i hae no idea about stuff like this. When i pull out in my truck, it feels great, but if i all the sudden slam onthe gas, it just kinda boggs down and feels like it has no power. the engine is a 390 4bbl, but the guy i bought it from put an autolite 2bbl carb on it and a 2" carb spacer. does it just need a bigger carb or is there some other problem? thanks!
This is the typical problem shared with every Ford 2V carb from 1963 thru 1979.
The accelerator pump diaphragm & check valve are in need of replacement.
Since I don't know what 2V carb you have, I can't post the part number for the accelerator pump.
The check valve is the same 1963/79 (C4AZ9576A Motorcraft CM825), but Ford changed the accelerator pump diaphragm in 1975.
The acc pump diaphragm is located on the front of the carb behind a cover with a lever. 4 bolts hold this cover on.
Be very careful when you remove the cover, there's a COIL SPRING behind it. The check valve is behind the pump diaphragm.
1974/76 390's came with a 2V carb as standard equipment, A 4V carb was an option.
When a 4V was factory installed on a 390, the engine code in the VIN is different.
The 4th digit of the VIN is the engine code: H = 390 2V / M = 390 4V / Y = 360 2V.
Is it really a 390? On sale day, 360 engines magically turn into 390 engines.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
How can it have a 2 barrel carb on it, if the intake manifold is for a 4 barrel?
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MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Sounds like the accelerator pump to me too, but I think having a 2 barrel carb on a 4 barrel intake is worthless. I think the main reason people do that is when they are selling a truck but want to keep the carb, so the throw something on there to keep it running so that it can be driven away.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Pull the air cleaner off the motor with the truck shut off, and look down the throat of the carb. Pull back on the throttle, and you should see two streams of gas shoot across the venturis. If you don't, the accelerator pump is not functioning. If you do, we'll move on to some other checks.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Check your base timing, and it wouldn't hurt to make sure your distributor vacuum advance holds vacuum. You can check this by applying vacuum to it and watching for the base plate in the distributor to move with the cap off. I myself wouldn't be wasting my time with a 2 barrel carb on a 4 barrel intake; I'd go ahead and put a 4 barrel on it.