1975 f700 361 backfire
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1975 f700 361 backfire
I have a 1975 f700 361 I recently replaced the points distributor with a HEI distributor. Since then every time I drive up a hill the motor backfires out the exhaust. And I don't know why. It doesn't do it when it is idling or diving on flat ground.
If someone could help me out I would really appreciate it, Thanks.
If someone could help me out I would really appreciate it, Thanks.
FTE Community Team
Joined: Nov 2001
Posts: 1,839
Likes: 252
From: Oak Harbor, Washington
Exhaust backfires can be caused by a lot of things. Limiting to things that only a distributor replacement could cause, and If it runs well otherwise, with NO idle or low-demand misfire, this could be caused by an arcing rotor, a failing HV coil, or (longshot here) a faulty centrifugal advance. These are all nearly impossible to diagnose without a oscilloscope (for the HV issues), a dial-back timing light or 'scope equivalent (for the mechanical advance check), or parts-swapping.
Back in the day, when parts were expensive and labor was cheap, you learned how to use expensive diagnostic equipment to pinpoint "the part" to replace; nowadays the economics are largely reversed in the US, so parts-swapping is how much of this diagnosis is done, as there are few left who would know how to track down this kind of thing, absent OBD hardware and "stored codes". We've all died off are are well into our dotage.
Me, I'd swap out the disty again, based on what you've told us.
On my '73 F600 (and other vintage non-GM vehicles that still run points) I go the Pertronix way, rather than swapping the entire disty. Since my '73 F600 has mechanical tach drive and the centrifugal vacuum regulator for the carb governor built-in to the base of the OEM disty, I'd never replace the stock stuff, only ditch the points & condenser. The OEM coil is more than adequate for any demand placed on the 361 in truck duty, since it'll never see 4500 RPM and is relatively low compression.
No good reason for the HEI disty, IMO. Except for bling.
---
My first Pertronix conversion was a '63 Falcon, in '01. And, I've put one on an antique Onan BFA 4.0 genset; took a bit of customization
The hardest part of a Pertronix conversion on a Six or Eight Ford is really running a switched 12v + wire to the coil, because it won't run on 8-9v reliably, and that's what Ford sends to the coil, except during cranking the starter. The ballast resistor is integrated into the wire harness and not easily bypassed. And Pertronix' instructions, while better now than 30 years ago, are still really unclear about that. They really want to sell you the coil, and that doesn't fix that issue anyway.
Back in the day, when parts were expensive and labor was cheap, you learned how to use expensive diagnostic equipment to pinpoint "the part" to replace; nowadays the economics are largely reversed in the US, so parts-swapping is how much of this diagnosis is done, as there are few left who would know how to track down this kind of thing, absent OBD hardware and "stored codes". We've all died off are are well into our dotage.
Me, I'd swap out the disty again, based on what you've told us.
On my '73 F600 (and other vintage non-GM vehicles that still run points) I go the Pertronix way, rather than swapping the entire disty. Since my '73 F600 has mechanical tach drive and the centrifugal vacuum regulator for the carb governor built-in to the base of the OEM disty, I'd never replace the stock stuff, only ditch the points & condenser. The OEM coil is more than adequate for any demand placed on the 361 in truck duty, since it'll never see 4500 RPM and is relatively low compression.
No good reason for the HEI disty, IMO. Except for bling.
---
My first Pertronix conversion was a '63 Falcon, in '01. And, I've put one on an antique Onan BFA 4.0 genset; took a bit of customization
The hardest part of a Pertronix conversion on a Six or Eight Ford is really running a switched 12v + wire to the coil, because it won't run on 8-9v reliably, and that's what Ford sends to the coil, except during cranking the starter. The ballast resistor is integrated into the wire harness and not easily bypassed. And Pertronix' instructions, while better now than 30 years ago, are still really unclear about that. They really want to sell you the coil, and that doesn't fix that issue anyway.
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