On my way to work this morning the truck was running properly. I had to slow down for a turning car and while getting back up to speed it suddenly started sputtering and backfiring through the exhaust. It will idle but starts backfiring and sputtering when you give it gas. It's getting fuel but maybe too much? It's got an edelbrock 600cfm on it. The only way I got it back to my house was by playing with my points. I thought they could have possibly shifted causing a poor spark. I can now get the truck up to 40mph with minimal backfiring but after that it's a no-go.
When I get back home, what do I need to look at first?

 

its mostlikely your airfuel mixture. get a meter so you can turn it down right. also make sure your idoling at the right speed. my truck used to backfire all the time till i did what i just described.

 

Investigate the points for pitting and burning, and gap them with a feeler gauge. Then set the timing with a light. Anytime you adjust the point gap, you must check the timing. Backfiring through the exhaust is often a timing issue.

 

The points were recently set with a feeler gauge. I can understand the points slowly going bad but these are fairly new. It literally went from driving great to crap in one second.
I might pull the ignitor box from my '76 F-250 and put my spare distributor on it. I hate points.

 

Points and time have been set.
Will crank and run fine in park and you can rev the engine. As soon as you try to drive down the road it starts stalling and sputtering.

 

I just fixed my 390 with the same problems check your filter for blockage, check your fuel pump make sure it runs fine, and if that doesn't fix it check your fuel lines everything make sure that there is no restriction. This probably is not the case with yours but someone hade used 1/8in copper tubing in place of my steel and in some spots rubber line severly restricting fuel flow there was enough to idle and fill the carb bowls, but as soon as you stepped on the gas there was not enough flow to keep up with the demand of the engine thus acting like it has run out of gas.

 

This is definitely not an issue of fuel getting to the carb. I'm going to go ahead and convert my system over to electronic distributor. Went and borrowed the stuff from my '76 F250. I have a feeling that the pin that holds the gear that connects to the camshaft that turns the distributor may have sheared. Like how I worded that? If it did shear, the gear could have turned ever so slightly.

 

Alright try pulling the Dis. if you can turn the gear and the rotor doesn't move a small weld has been broken if they spin tegether well then i would think that you are on the right track

 

How many miles are on the engine? Possible the timing chain jumped. I have had that happen before.

 

The gear ended up being just fine. I guess the points took a dump even though they are fairly new. I put the Duraspark 1 on there temporarily and she runs good now.
I guess I'll upgrade her permanently fairly soon.

 

About 1100 since rebuild.

 

I bet the camshaft timing-pin snapped throwing the cam timing off. Verify this by bringing cylinder #1 to TDC and seeing the relation of the rotor to #1 on the cap.

Josh

 

Nope. Pin is good. I thought that might be it but it checked out fine.
Anybody know the correct part number for the Pertronix electronic conversion? I can't find the right thing for a '74 Ford F100 with 390.
The engine might even be a '69 or '70.
I found the crane cams which is magnetic,
Crane Cams 750-1700 - Crane XR-i Points-To-Electronic Ignition Conversion Kits - Overview - SummitRacing.com
And the Accel which is optical,
ACCEL 2020 - ACCEL Points Eliminator Conversion Kits - Overview - SummitRacing.com

What's the best to go with?

 

Pertronix:

Distributors originally with POINTS

Ignitor I 1281
Ignitor II 91281
Ignitor III 71281