Hey y'all,,
I have a 1987 F250, carb'd 460. I recently had a distributor go bad. I took the time to also install a new edelbrock performer carb (500 cfm). With the new distributor and carb installed, the trucks starts and runs great at idle. The initial timing is set with the vacuum hose disconnected from the distributor and plugged with a small bolt. Here's my problem: When I hook up the vacuum advance, the truck instantly dies "poof". if you give it a little throttle and start it, it backfires like crazy and stumbles fiercely as well. Disconnect the vacuum advance and it runs perfectly again. I'm a bit perplexed by this... Ive owned this truck for 20 years and have pulled the distributor and re-timed it a thousand times and have never ran into this before...does anyone have any ideas?

Additional details:
had 500 cfm edelbrock for 15 years, put a 600 cfm edelbrock on it when I rebuilt the motor 3 years ago, but since the cam is stock, it never ran quite as well as it did with the 500 so I switched back to the 500 when I ran into distributor trouble (500 was rebuilt by a local guy that rebuilds carbs for a living)

I always set the base timing at 10 degrees. Its marked on the balancer with a white marker that I put on there 20 years ago...when I time the engine, I let it warm up, with vacuum advance disconnected and plugged. I loosen the distributor, set it at 10 degrees with the timing light, then I unplug the vacuum advance and hook it back up to the distributor and then lock it down. - following those same procedures (that ive done for the last 2 decades), when I hook up the vacuum advance it instantly dies :/

Should also add that all of the emissions have been totally removed, has a Weiand intake and the smog ports on the back of the heads have been plugged for years. To my knowledge there are no vacuum leaks on this motor.

The advance is hooked up to the port on the right side of the carb that has steady vacuum (I think this is the port that I have always had that hooked up to, but I admit that I think im getting old and forgetful and it may have been hooked up on the other side....)

All thoughts and ideas are welcome. Thanks guys.

 

distributer in backwards?

 

I don't think so. I rotated the engine around to TDC with a ratchet and socket, and installed the distributor so the rotor was pointing at cylinder #1 when you put the cap on. When I time it, i'm timing it off cylinder #1 and everything lines up where it should on the balancer

 

That's where I'd start, especially if you swapped the carb recently. Even if your memory's fine, the 500 might be set up differently than the 600 it replaced. I haven't messed with carbs a whole lot but I've read mixing up manifold vacuum and ported vacuum can cause timing issues.

 

Hook the advance to the ported vacuum, its the port on the front thats higher than the other, left side i believe.

 

I hooked it up to the ported vacuum (passenger side of carb) and retimed it to 10 degrees (again). runs great at idle, give it throttle it backfires and pings and stumbles like crazy and dies. Take the vacuum off the distributor and plug it, it run well at throttle and idle. I can't use vacuum off either port on the carb. All I can figure is the vacuum advance on the distributor is somehow defective? Maybe its radically advancing when hooked up?