Strange engine issue need some input
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New User
Joined: May 2007
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From: San Jose
Strange engine issue need some input
I picked up a '70 F250 390 4 barrel carter and edelbrock manafold yesterday, and driving it home the truck would go over 50MPH as it would sputter and backfire and just run like junk.
we did check the timming at it was set at 6 - 10 BTDC and accourding to couple books that came with the truck that is normal.
Today I rebuilt the carb (carter afb) and added a Pertronix Ignitor Ignition.
The engine runs much better now with good throttle responce and revs with no problems the vucuum is bouncing between 19.5 - 20 in. with 800 rpm's.
The strange part is the engine wants to run at 25 degrees ATDC (if I try to go much lower the engine will not run) I did remove the distributor but when I put it back the rotor and distibutor were in same location as removed.
Any ideas on why it want's 25 degrees ATDC after the ignition upgrade? could I have put the distributor in wrong?
I just ran a check with a vacuum gauge, if I snap the throttle wide open and then close it drops to 0 at the hit of the throttle and then to 25 and back to 19.5 - 20 after I let off the throttle. that sounds how it should be.
The owner did say it had a burnt valve but I'm not sure about that now. will do a compress check next weekend..
we did check the timming at it was set at 6 - 10 BTDC and accourding to couple books that came with the truck that is normal.
Today I rebuilt the carb (carter afb) and added a Pertronix Ignitor Ignition.
The engine runs much better now with good throttle responce and revs with no problems the vucuum is bouncing between 19.5 - 20 in. with 800 rpm's.
The strange part is the engine wants to run at 25 degrees ATDC (if I try to go much lower the engine will not run) I did remove the distributor but when I put it back the rotor and distibutor were in same location as removed.
Any ideas on why it want's 25 degrees ATDC after the ignition upgrade? could I have put the distributor in wrong?
I just ran a check with a vacuum gauge, if I snap the throttle wide open and then close it drops to 0 at the hit of the throttle and then to 25 and back to 19.5 - 20 after I let off the throttle. that sounds how it should be.
The owner did say it had a burnt valve but I'm not sure about that now. will do a compress check next weekend..
Last edited by sned45; May 13, 2007 at 11:26 PM.
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Joined: May 2007
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From: San Jose
Just did a double check it's 25 degrees BTDC not ATDC like I had thought. I'm just so used to timming on the other side of the engine. But still leaves the issue of so much timming.
did this all with the vacuum not connected to the dis.
I think next weekend I'm going to pull the dis next weekend and reset it.
but still wondering why it wants to run at 25 degrees BTDC. Is one tooth worth 19 degrees?
did this all with the vacuum not connected to the dis.
I think next weekend I'm going to pull the dis next weekend and reset it.
but still wondering why it wants to run at 25 degrees BTDC. Is one tooth worth 19 degrees?
Last edited by sned45; May 14, 2007 at 12:42 AM.
Senior User
Joined: May 2007
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From: woodward/okmulgee, ok
if it were, it should adjust out if you're only one tooth off, but you could be 2 or 3 as i believe the oil pump drive is a hex shape. i would pull the dizzy out and put engine at tdc and start over.
Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
Check the timing marks, the balancer may be sliped around. Bring the engine up to TDC on #1 firing stroke by pulling #1 plug. Then look to see where the timing marks are and where the rotor is pointing, it should be pointing at #1 on the cap.
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