Getting the bugs worked out!
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Getting the bugs worked out!
I picked up a '2wd 76 F100 with a 360 late last fall and have been working getting things going to make it drivable. When I bought the the truck it had been sitting for a couple of years being started just now and again. Only thing that I could find wrong was a slight hesitation when you got on the gas a little too quickly.
Since I bought the truck i've given it a tune up and a few extras:
Carb rebuild
Fuel Pump
Fuel Filter
Air Filter
Battery
New vacuum hoses
Thermostat
Cap and Button
Plugs and Wires
Oil Change
Manual Choke
The truck starts fine warms up and idles great. Still has a bad hesitation when you step on the gas but now it also seems to do it while driving. Going down the road it idles fine,but if you give it gas it trys to die. Can't find any vacuum leaks anywhere. I'm not sure if this would be that the carb mixture is off, bad power valve, or the fuel filter being clogged.
I'm not sure where to go from here,but any help would be appreciated!
Since I bought the truck i've given it a tune up and a few extras:
Carb rebuild
Fuel Pump
Fuel Filter
Air Filter
Battery
New vacuum hoses
Thermostat
Cap and Button
Plugs and Wires
Oil Change
Manual Choke
The truck starts fine warms up and idles great. Still has a bad hesitation when you step on the gas but now it also seems to do it while driving. Going down the road it idles fine,but if you give it gas it trys to die. Can't find any vacuum leaks anywhere. I'm not sure if this would be that the carb mixture is off, bad power valve, or the fuel filter being clogged.
I'm not sure where to go from here,but any help would be appreciated!
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What's the best way to check the advance,and where should I be getting a ported vacuum source from?
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Something that I forgot to include is that the transmission seems to be shifting fairly rough. Doesn't seem to be mechanically related, but more on the line of the vacuum not being hooked up correctly...If anyone has a diagram for the vacuum,or could point me in the right direction for what-goes-where, I think that would solve a lot of things.
Montana,checked the advance today, and was getting a constant vacuum...Got it hooked up with the spark delay valve to a ported source (I think!) and tried it out.
The hesitation when pulling out from a stop or stepping on it too quickly is gone!
Montana,checked the advance today, and was getting a constant vacuum...Got it hooked up with the spark delay valve to a ported source (I think!) and tried it out.
The hesitation when pulling out from a stop or stepping on it too quickly is gone!
Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
Something that I forgot to include is that the transmission seems to be shifting fairly rough. Doesn't seem to be mechanically related, but more on the line of the vacuum not being hooked up correctly...If anyone has a diagram for the vacuum,or could point me in the right direction for what-goes-where, I think that would solve a lot of things.
Montana,checked the advance today, and was getting a constant vacuum...Got it hooked up with the spark delay valve to a ported source (I think!) and tried it out.
The hesitation when pulling out from a stop or stepping on it too quickly is gone!
Montana,checked the advance today, and was getting a constant vacuum...Got it hooked up with the spark delay valve to a ported source (I think!) and tried it out.
The hesitation when pulling out from a stop or stepping on it too quickly is gone!
If you were getting constant vacuum at idle from your vacuum advance hose then someone had it connected to manifold vacuum which doesn't necessarily mean connected directly to the intake manifold (connected to the carb below the throttle plates is still manifold vacuum) and it pulls in all your vacuum advance at idle leaving a flat spot or hesitation just off idle, a ported vacuum source will pull no vacuum at idle, some guys with a lopey cam may choose to pull manifold vacuum for their advance to smooth out a rough idle and/or run cooler, but for a basically stock engine ported (above the throttle blades) is the preferred source for vacuum advance.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The hesitation sounds like an accelerator pump issue. With the engine off, look down the throat of the carburetor and pull the throttle back. You should see two nice streams of gas shoot against the venturis.
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The modulator is located on the side of the transmission, right? Where should it be pulling vacuum from?
Post Fiend
Joined: Apr 2008
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From: Big Sky Country
If i remember correctly the modulator is on the rear right side of the transmission just above the pan and it should pull manifold vacuum.
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Got to check some stuff out between the bursts of rain today....So far the accelerator pump and modulator checked out, everything is hooked up and working. Anyone know if the EGR valve should be ported or constant? The EGR, choke pulloff, and vacuum canister are all I have left to check out (as far as vacuum connections.)
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
EGR = ported vacuum (through a temperature-controlled vacuum switch called a PVS)
Choke pulloff = manifold vacuum (present at idle).
When you say vacuum canister, do you mean the thing that looks like a coffee can?
There's no such thing as constant vacuum because manifold vacuum drops off as the throttle plates open and manifold negative pressure equalizes to atmospheric pressure.
Choke pulloff = manifold vacuum (present at idle).
When you say vacuum canister, do you mean the thing that looks like a coffee can?
There's no such thing as constant vacuum because manifold vacuum drops off as the throttle plates open and manifold negative pressure equalizes to atmospheric pressure.
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EGR = ported vacuum (through a temperature-controlled vacuum switch called a PVS)
Choke pulloff = manifold vacuum (present at idle).
When you say vacuum canister, do you mean the thing that looks like a coffee can?
There's no such thing as constant vacuum because manifold vacuum drops off as the throttle plates open and manifold negative pressure equalizes to atmospheric pressure.
Choke pulloff = manifold vacuum (present at idle).
When you say vacuum canister, do you mean the thing that looks like a coffee can?
There's no such thing as constant vacuum because manifold vacuum drops off as the throttle plates open and manifold negative pressure equalizes to atmospheric pressure.
Just happened to check the accelerator pump again, and wasn't getting any gas. Happened to have an extra in my carb kit,so guess I'll try that tomorrow after work!The thing I was referring to as the vacuum canister is the black piece mounted by my valve cover:
http://i55.photobucket.com/albums/g1...1Image0004.jpg