Frustration is setting in.
Thread Starter
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Junior User
Joined: Dec 2001
Posts: 84
Likes: 0
From: Burnaby BC, Canada
Frustration is setting in.
Good day to all,
I am having problems with my '72 F-250 Camper Special, 390ci, c-6,
Carter 600 manual choke 4bbl, Pertornix ignitor and flamethrower coil.
The thing will idle all day long and not miss a beat, it also runs fine when I apply gas gently. If I put my foot into it, it backfires terribly through the carb. It was suggested that I may have a worn distributor shaft but I've checked it and it does not appear to have any 'slop', it feels as it should. I changed the cap and rotor thinking that perhaps the cap was cracked but this has not made a difference. I've gapped the plugs to .44, set the timing at 12 degrees, adjusted the carb with a vacuum gauge so that it is getting the best vacuum and checked the fuel pump pressure which is a steady 4.5psi and does not bleed off over the time specified with the tester.
What am I missing? Does anyone have any suggestions? I need to take this thing on a trip soon and need it running it's best.
Thanks in advance for the help.
I am having problems with my '72 F-250 Camper Special, 390ci, c-6,
Carter 600 manual choke 4bbl, Pertornix ignitor and flamethrower coil.
The thing will idle all day long and not miss a beat, it also runs fine when I apply gas gently. If I put my foot into it, it backfires terribly through the carb. It was suggested that I may have a worn distributor shaft but I've checked it and it does not appear to have any 'slop', it feels as it should. I changed the cap and rotor thinking that perhaps the cap was cracked but this has not made a difference. I've gapped the plugs to .44, set the timing at 12 degrees, adjusted the carb with a vacuum gauge so that it is getting the best vacuum and checked the fuel pump pressure which is a steady 4.5psi and does not bleed off over the time specified with the tester.
What am I missing? Does anyone have any suggestions? I need to take this thing on a trip soon and need it running it's best.
Thanks in advance for the help.
Thread Starter
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Junior User
Joined: Dec 2001
Posts: 84
Likes: 0
From: Burnaby BC, Canada
Frustration is setting in.
Just went out and checked, there is a definite steady stream with no sputtering. The carb is only a couple months old. When I punch the throttle when it is sitting and idling in neutral, it seems to get just past the 'accelerator pump' stage before the backfiring starts.
Post Fiend
Joined: Feb 2000
Posts: 5,130
Likes: 8
From: Brea CA
Frustration is setting in.
Ok, a couple more things. First, try disconnecting and plugging the vacuum advance and see what that does. Next, do you have the ground strap connected from the movable breaker plate to the housing?
Barry
Barry
Thread Starter
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Junior User
Joined: Dec 2001
Posts: 84
Likes: 0
From: Burnaby BC, Canada
Frustration is setting in.
Well, I don't drive the truck very much, only about 25km's a week. It did run fine at one time, can't pinpoint the time that this started happening though. All I've done to it is replace the plugs, replace the carb, cap, rotor, wires, Pertroix ignition etc. I think I really noticed it driving home a different way one day where there is a very steep hill where I had to put my foot into it to get it going. I generally drive the truck very gently. I pulled the plugs today to check them and they were all very clean and the picture of 'perfect plugs'. I'm very willing to keep taking potshots at the darn thing. One fellow at work suggested a weak fuel pump. Is 4.5psi a good pressure?
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Elder User
Joined: Jun 1999
Posts: 940
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From: LAT 46.55501° & LON -122
Frustration is setting in.
I would close the gaps on the plugs back to .035 and give it a try. It is possible that something in your ignition system still can't handle the larger gap such as the wires.
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Thread Starter
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Junior User
Joined: Dec 2001
Posts: 84
Likes: 0
From: Burnaby BC, Canada
Frustration is setting in.
Thanks, I'll try that next. It'll have to wait until tomorrow though as I have to head out for a meeting right now. I'll let you know what happens.
Post Fiend
Joined: Feb 2000
Posts: 5,130
Likes: 8
From: Brea CA
Frustration is setting in.
That's what I was thinking too, Like M. Might also be crossfiring on the 'ol 7-8. When your pump shot is used up the motor sounds lean which requires a higher firing voltage. The ignition may not be up to snuff or you're running too lean already. Float level and jetting are the next step, no power valve in the Carter.
Barry
Barry
New User
Joined: Apr 2002
Posts: 8
Likes: 0
From: Winston-Salem USA
Frustration is setting in.
Hey Don,
As an owner of a couple of 67's trucks. A couple of questions. WHat is the mileage of you truck? Is the engine original? If it is has any major repairs have been done to your engine? Guessing if the engine is original. You may have a loose timing chain. But then I have seen carbs idle fine but stumble,spit and sputter when the throttle is pushed. Changing or swapping a carb is about the only way to be sure though.
So here's my train of thought.1) Check base engine timing. One way to check timing chain for looseness is to. Bring you eng up to tdc mark the rotor,slowly rotate the eng amd see how much movement is required before the rotor moves. Move it both ways to check for total amount of slack in your timng chain. 2)If possible check disturbitor timing and advance to see if the vacum avance is working. 3)then lastly diagnose the carb. Easiest way would be to swap a different carb to see if any difference. Hope this helps.
As an owner of a couple of 67's trucks. A couple of questions. WHat is the mileage of you truck? Is the engine original? If it is has any major repairs have been done to your engine? Guessing if the engine is original. You may have a loose timing chain. But then I have seen carbs idle fine but stumble,spit and sputter when the throttle is pushed. Changing or swapping a carb is about the only way to be sure though.
So here's my train of thought.1) Check base engine timing. One way to check timing chain for looseness is to. Bring you eng up to tdc mark the rotor,slowly rotate the eng amd see how much movement is required before the rotor moves. Move it both ways to check for total amount of slack in your timng chain. 2)If possible check disturbitor timing and advance to see if the vacum avance is working. 3)then lastly diagnose the carb. Easiest way would be to swap a different carb to see if any difference. Hope this helps.
Senior User
Joined: Nov 2001
Posts: 294
Likes: 0
From: Calgary Canada
Frustration is setting in.
I had a very frustrating episode with my 302. Turned out to be a spark plug with a crack in the porcelain. I found it by looking real close at the plugs when it was idling in the dark. Maybe you could try blipping the throttle while watching to see if you can spot something arcing.
Thread Starter
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Junior User
Joined: Dec 2001
Posts: 84
Likes: 0
From: Burnaby BC, Canada
Frustration is setting in.
Thanks for all the help folks. I don't know too much about the truck other than the motor was replaced 5yrs ago with a rebuilt from a reman place here in town. Now that I've regapped the plugs and reset the timing etc, etc, for the millionth time it seems to be running better. I haven't really taken it out for a run yet, I'll be doing that tomorrow. It is not idling very well now though. It seems to have cured the backfiring but is idling like cr#p.
I'll let you know how it behaved when I return from my dive trip tomorrow.
I'll let you know how it behaved when I return from my dive trip tomorrow.
Elder User
Joined: Jun 1999
Posts: 940
Likes: 0
From: LAT 46.55501° & LON -122
Frustration is setting in.
Did you actually change the timing at all this last time or did you just check it. Retarding the timing will lower the idle RPM and thus possibly make it idle poorly.
Posting Guru
Joined: Mar 2002
Posts: 1,217
Likes: 0
From: Yelm Washington usa
Frustration is setting in.
I had a 360 in my 72 f-250 and I had the exact same problem. After replacing it with a 390 we took the carb off it and put on the 390, works great. While the 360 was in the truck I replaced the carb (3 times), timing chain and gears, ground wires (it looked like a spider web) distributor(2 times) Caps and rotors and points fuel pumps and filters. After pulling the engine I tore it down just tok ow what the prob was and the only thing we could find wrong was some slightly bent push rods.
hope that helps.
dj
hope that helps.
dj