Car starts, runs fine then runs bad after 5 mins....pulling hair out!!!???

[AKcharger]

OK guys I'm pullin' my hair out here and have run out of stuff to change...here's what I got. Car starts/runs fine then after about 5 mins it runs like crap, doesn't want to stay running, wants to stall and sounds like it backfires (very lightly) though the exhaust.  problem is somewhat new, it started a few months ago, before that it was fine. here's what I did:

- Swapped carb over from one on my '70...same and the old carb works fine on the '70
- Swapped out Ballast resistor, I thought that was it as it would get Super hot (250°) but it's the same, new one get hot too
- New MSD blaster 2 coil
- Swapped out ECU

I can ONLY think of 1 thing...the Distributor. I replaced the distributor not too long ago with a new "Firecore" distributor I did a major tune-up with new plugs/wires/distributor but  seemed OK after I did all that, at least right away. So here's what I'm thinking:

- Bad plug wire or a wire is laying on a manifold...yup thought of that, wires routed correctly and when it starts running bad it's not like it's dropping 1 cylinder but 2 or 3...so having 3 bad plug wires??? unlikely
- Distributor? It's the only thing left that I can see

Suggestions and or what am I missing??? 

[70 sublime]

Try running it with gas cap open ?
Vent plugged ?

[BLK 68 R/T]

I was thinking fuel as well, crud in the tank blocking the filter sock after a few minutes. As soon as you shut it off the pump quits sucking and the debris releases from the sock until you start it again and it clogs itself back up again.

[birdsandbees]

Break out the outboard kicker can and see what it does..

[AKcharger]

Gas?? Humm sure I'll give that a try. Although I did replace the gas tank years ago...but at this point it's ANYTHING
...Expect slight delay in feedback, have to go back to work so stby

[maxwellwedge]

Are you running a vapor separator? Could be one of the bad ones. Similar symptoms to what you are describing.

[AKcharger]

Well, at Dino's suggestion I replaced the distributor...that seems to be it, it's not acting up after I replaced the fire core with the stock one. Heading off to work now, I'll play with it more in a week

[69Chrgr]

I have the same issue with my engine as of late. My Firecore distributor is acting the same way. It even left me stranded at a cars show as one of the pins that plugs into the MSD had pushed out. Before that, my Firecore coil crapped the bed. Took the cap off and mine is corroded as hell.

[AKcharger]

Well it was the Firecore distributor  Took car out for an extended drive and problem vanished. No backfires, no stumbles fire. Yet another example of what happens whey you stray from OE parts

[NHCharger]

How old is the Firecore? Is it a RTR unit?

[firefighter3931]

Bill, did you check to make sure the pickup was tight and gapped properly ?

Many thousand FC distributors are out there in service with zero issues. That's not say that there aren't defects but that is the exception rather than the rule. Did you try installing the old ballist resistor to see if that was the issue ?



Ron

[AKcharger]

NH - Distributor was purchased from Mancini in Oct of 2016, installed about this time last year and hasn't run right since...unknow what an "RTR is, it's just a normal B-block one

Ron - No, but the time I got your suggestion I'd already swapped it out back to stock, plus I don't have a copper feeler gauge. Howered I did look over all the components for obvious defects and everything looked clean and new. I replaced the ballast resistor and it was the same. EVRYTHING changed when I replaced the distributior so that's a "confirmed kill"

I did talk to Rick at Fire core and explained what happened and he said they'll stand behind it, so I'ts going to be returned in the coming days.

[69Chrgr]

Dam - Glad you posted this. That's EXACTLY how my car is behaving with my Firecore distributor. It started with the RPM jumping a couple of hundred RPM sporadicly while idling, and now it backfires as well. I guess I need to move forward with the FI and Holley dual sync and put that thing behind me. Thanks for sharing.

[AKcharger]

Update, got the firecore back but haven't reinstalled it. They said the pick up was loose, funny I never touched it. anyway I'll put it back in one day, till then the stock one is running fine