351 HO carb
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Junior User
Joined: Nov 2011
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351 HO carb
Need help! My 1985 F150 w/351 HO wants to fire when gas is poured down carb. Replaced fuel pump (mech) and filter. Strong spurts of gas out of metal line at carb when cranked, but gas not reaching venturi. This is not original carb. Engine rebuilt at 80k (oil failure), replaced carb at 110k but could not match existing unit, substituted a similar model Ford/Holly 4V. Current mileage is 135k.
Any thoughts on what's going on and what to do next? Thanks.
Any thoughts on what's going on and what to do next? Thanks.
Moderator
Joined: Nov 2007
Posts: 22,415
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From: Denver Metro Area, CO
With the engine off, remove the air cleaner assembly and look down into the throat of the carb as you fully open the throttle with your hand. You should see two strong streams of gasoline being injected into the plenum; do you see that?
Laughing Gas
Joined: Feb 2010
Posts: 781
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From: Sanford, NC
The carb is probably stopped up from gummed up gasoline and dirt if the filter had
not been regularly changed. It needs to be rebuilt with either a Motorcraft or Holley
kit and then should be good as new.
not been regularly changed. It needs to be rebuilt with either a Motorcraft or Holley
kit and then should be good as new.
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
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Joined: Nov 2007
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From: Denver Metro Area, CO
Yeah, I agree with the other two guys - rebuild it.
At a minimum, it needs a new Accelerator Pump, and rebuilding it will give you that (plus a new float valve, etc. etc.).
At a minimum, it needs a new Accelerator Pump, and rebuilding it will give you that (plus a new float valve, etc. etc.).
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pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
Gasoline (if you can call it that these days) will dissolve all kinds of things.
When it sits in the carburetor, it evaporates, but leaves behind deposits.
Rubber pieces and gaskets get old and dry out.
They don't seal or flex the way they should.
Diaphragms develop holes when they get stiff.
Varnish left behind clogs small orifices and gums parts like check ***** in place.
The screen at the inlet is good at removing sediment but not much else.
When it sits in the carburetor, it evaporates, but leaves behind deposits.
Rubber pieces and gaskets get old and dry out.
They don't seal or flex the way they should.
Diaphragms develop holes when they get stiff.
Varnish left behind clogs small orifices and gums parts like check ***** in place.
The screen at the inlet is good at removing sediment but not much else.
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Junior User
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Okay, I removed the front fuel bowl, and it was completely dry. I noticed that the valve stem that the float controls is stuck in the closed position. Going to try to clean it; if that doesn't work I will replace. Anyone remember which way the filter goes in? I forgot. Currently I have the inside cone pointing up to the carb.
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
I've never used the metal sponge filters, only the plastic cup screen ones.
If the bowl is dry you can pretty much bet that the viton tip on the needle valve is shot.
Don't for get to flush the transfer tube to the secondary bowl and check those seals at either end where it enters front and rear.
If the bowl is dry you can pretty much bet that the viton tip on the needle valve is shot.
Don't for get to flush the transfer tube to the secondary bowl and check those seals at either end where it enters front and rear.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
A couple of "don'ts" in my book. First, don't forget to lube the o-rings on the transfer tube or you will probably have a leak since they tend to try to roll over the land on the transfer tube that is to hold them in place, and when they do that they get pinched between the tube and the bowl.
Second, don't rely on the filter that goes in the carb - even the plastic one Jim suggested. It is a good "last resort" filter, but even it doesn't stop the really fine stuff I see in these old tanks all the time. Use a plastic see-through in-line filter as they stop a lot more "stuff", and I've had that "stuff" clog up the accelerator pump discharge nozzles more than once w/o a good filter.
Second, don't rely on the filter that goes in the carb - even the plastic one Jim suggested. It is a good "last resort" filter, but even it doesn't stop the really fine stuff I see in these old tanks all the time. Use a plastic see-through in-line filter as they stop a lot more "stuff", and I've had that "stuff" clog up the accelerator pump discharge nozzles more than once w/o a good filter.
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Junior User
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Well, had to buy rebuild kit just for a new gasket on the front bowl, so went ahead and replaced inlet valve and accel pump. Old valve started working after soaking in carb cleaner, but replaced anyway. Found out which end points where on the filter.
Right on about the transfer tube! After reassenbling, cranked a few times but before the bowl could fill up gas started shooting out at the transfer tube. Will put another o-ring in tomorrow and try again, but I think I've got it licked. Wasn't too bad for a first time with a carb. Just glad I didn't have to remove it.
Right on about the transfer tube! After reassenbling, cranked a few times but before the bowl could fill up gas started shooting out at the transfer tube. Will put another o-ring in tomorrow and try again, but I think I've got it licked. Wasn't too bad for a first time with a carb. Just glad I didn't have to remove it.