Weird really HELP!
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Weird really HELP!
1971 302 2b
Runs fine idles fine in park or N
put it in drive and let it idle it wants to surge like u giving it gas and letting off
put it back it N or P and it idles smooth or give it a little gas and drive at 5 mph its fine
just not sitting in drive it wont idle
Runs fine idles fine in park or N
put it in drive and let it idle it wants to surge like u giving it gas and letting off
put it back it N or P and it idles smooth or give it a little gas and drive at 5 mph its fine
just not sitting in drive it wont idle
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Now i am really scratchin my head
Take off the vacuum line going to the nipple on the distributor the nipple closest to the cap
it will idle fine in drive with foot on brake...put it back on and it starts surging again
Take off the vacuum line going to the nipple on the distributor the nipple closest to the cap
it will idle fine in drive with foot on brake...put it back on and it starts surging again
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And it didnt start doing this till after I sucked Seafoam into the PVC vacuum going into the back of the intake..
Ether that has caused it or its just freak that it started this right after the Seafoam
Ether that has caused it or its just freak that it started this right after the Seafoam
Elder User
Joined: Dec 2007
Posts: 813
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From: Up Nort Minnesota
you got a 2v motorcraft carb on that thing?
I think you might be barking up the wrong tree.
It's a good idea to test all diaphrams such as your vacuum advance diaphram on the dist and the choke pull off on the carb.
Those are just good things to check always.
But I'm wondering about maybe your power valve on the carb.
If the power valve diaphram cracks from age it will leak fuel into the bottom side of the valve. The bottom side of the valve should be dry, air only, no fuel. If the diaphram in the P-valve is leaking then it's dripping or flowing/dribbling fuel into your intake at the base of the carb in an un-metered and erratic manor.
Hence the surging that you just can't tune out.
I'm doing a carb right now, i'll maybe try to snap a few pics for you.
if the diaphram in the P-valve is badly torn then the engine will simply be drowning in raw fuel, crazy rich. You can turn the idle mixture screws closed & it will still run.
but if it's just a minor crack, it will surge like you are explaining.
This might not be what's wrong with your truck but it's what came to mind reading your post.
I think you might be barking up the wrong tree.
It's a good idea to test all diaphrams such as your vacuum advance diaphram on the dist and the choke pull off on the carb.
Those are just good things to check always.
But I'm wondering about maybe your power valve on the carb.
If the power valve diaphram cracks from age it will leak fuel into the bottom side of the valve. The bottom side of the valve should be dry, air only, no fuel. If the diaphram in the P-valve is leaking then it's dripping or flowing/dribbling fuel into your intake at the base of the carb in an un-metered and erratic manor.
Hence the surging that you just can't tune out.
I'm doing a carb right now, i'll maybe try to snap a few pics for you.
if the diaphram in the P-valve is badly torn then the engine will simply be drowning in raw fuel, crazy rich. You can turn the idle mixture screws closed & it will still run.
but if it's just a minor crack, it will surge like you are explaining.
This might not be what's wrong with your truck but it's what came to mind reading your post.
Elder User
Joined: Dec 2007
Posts: 813
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From: Up Nort Minnesota
Here man, this is a power valve & this is where it goes, front bottom side of the carb.
It screws in there & the top side protrudes right up inside the float bowl. That top side is a valve. Tthe diaphram in the bottom end is drawn by vacuum and opens the fuel valve. See the 2 holes in the bore where the valve screws in? That's where the fuel is supposed to flow when the vacuum opens the diaphram under heavy engine load. The single hole on the outside of the bore is for vacuum, when the diaphram is cracked fuel leaks into that vacuum port, which is wrong.
It screws in there & the top side protrudes right up inside the float bowl. That top side is a valve. Tthe diaphram in the bottom end is drawn by vacuum and opens the fuel valve. See the 2 holes in the bore where the valve screws in? That's where the fuel is supposed to flow when the vacuum opens the diaphram under heavy engine load. The single hole on the outside of the bore is for vacuum, when the diaphram is cracked fuel leaks into that vacuum port, which is wrong.
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So I think I will just get a new carb thursday
I spayed a 1/2 can of carb cleaner in it yesterday while it was running
I spayed a 1/2 can of carb cleaner in it yesterday while it was running
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then why wont it do it in park? or surge going slow?
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Elder User
Joined: Dec 2007
Posts: 813
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From: Up Nort Minnesota
Yeah that's not really how carb cleaner works.... you might have cleaned your ports & valves a little though 
Carb kits aren't that tricky.
Yust take your time, keep track of all of your little clips & stuff. It's easy to drop some of those little C-clips. magnetic flat blade screw driver can be pretty helpful with C-clips in tight places like on the choke side of the carb.
oh wait, my bad..
I just went back & read that you wrote "new carb" not kit.
Yeah that'll work too man but it'll probably set you back $260-$280
Carb kits aren't that tricky.
Yust take your time, keep track of all of your little clips & stuff. It's easy to drop some of those little C-clips. magnetic flat blade screw driver can be pretty helpful with C-clips in tight places like on the choke side of the carb.
oh wait, my bad..
I just went back & read that you wrote "new carb" not kit.
Yeah that'll work too man but it'll probably set you back $260-$280
Elder User
Joined: Dec 2007
Posts: 813
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From: Up Nort Minnesota
well, you really seem to thing it's related to park, drive neutral....
try something then, get a vacuum nipple cap or make one with a short pieve of vac line with a screw or small bolt in the end.
now in the back of the engine there will likely be kind of a vacuum tree.....
forget that... here's where I'm trying to go with this, there is a vacuum linefrom your transmission that runs up to the back of the engine. It will be a metal line right up to the top end where a rubber vac line conects it to the intake manifold (possibly at a "vacuum tree" like I mentioned above.)
cap that port. Unplug the line going to the trans & cap the port the line was plugged into.
then try your stuff with park neutral drive.
for kicks
Senior User
Joined: Dec 2008
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From: salt lake
as i read this it sounds like you have a vacuum leak not a carb issue. it idles fine in park and neutral and at low speed cus you are not putting any pressure on the motor, when you put it into a gear you add residence on the motor making your issue. before you go spending a lot of $$ check all your vac lines it could be a small leak and not make any sound.
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as i read this it sounds like you have a vacuum leak not a carb issue. it idles fine in park and neutral and at low speed cus you are not putting any pressure on the motor, when you put it into a gear you add residence on the motor making your issue. before you go spending a lot of $$ check all your vac lines it could be a small leak and not make any sound.
But it runs fine beyound idle in Dand it has pressure on the motor going up hill at 20mph and it runs fine