Surging issue.

[YBeNormal]

Hey guys I need some help. I just got an 89 RV it has a ford 460 with a Holley 4 barrel all factory. It sat for a little while and while driving it started to get a deceleration backfire and then started developing a surge at idle especially while stopped at a light.

Rebuilt the carb and it's better now but still noticeable and the backfire has gotten worse.[S

Can anyone point me in a good direction to start?

 

[christcrusader13]

Does it fall on it's face when you try to accelerate? what number is the Holley you are running?

 

[Willowbilly3]

Does it have air injection? The diverter valve might be bad causing the backfire. Check for some kind of vacuum leak and also check the egr valve to make sure it isn't hanging open. I'd say it sounds like a lean condition.

 

[smallfoot]

All the above are ideas. If it has sat awhile, it might be gas related. Even rebuilding the carb doesn't help if the fuel lines are rubber and have started breaking down. It'll suck little pellets of broken down rubber right back into the filters quickly. New filters and rubber hose parts will tell. A vacuum leak(intake or hose) would be my best guess otherwise by what you're describing.

 

[YBeNormal]

Does it fall on it's face when you try to accelerate? what number is the Holley you are running?

No sir Runs great. Looking for vac leaks and checking lines and not really finding anything bad or deteriorated

 

[Yankee Transplant]

I had a ford run ruff at times and back fire it turned out to be the star gear in the distributor was stripped ,, sometimes it would spin some time it would slip on the shaft . mine was electronic dist. just a thought [S

 

[Yankee Transplant]

you ever get it figured out ?

 

[sgtpontiac]

I'd say go back to basic's...

Is it running the old fuel? what is the Fuel pressure....does it have a return fuel line....(could be by passing fuel and losing pressure)..going lean or not keeping fuel bowl full......is the timing to far advanced or retarded...if the timing looks ok could the damper be spun? What is the condition of the distributor...could the advance weights be sticking? does it have that ignition brain box / module? Could it be going bad? although that usually will cause no start or intermittant shutting down.....there is a number of things I'd personally check prior to carb issues or intake leaks....JMHO....

 

[YBeNormal]

Is it running the old fuel? what is the Fuel pressure....does it have a return fuel line....(could be by passing fuel and losing pressure)..going lean or not keeping fuel bowl full......is the timing to far advanced or retarded...if the timing looks ok could the damper be spun? What is the condition of the distributor...could the advance weights be sticking? does it have that ignition brain box / module? Could it be going bad? although that usually will cause no start or intermittant shutting down.....there is a number of things I'd personally check prior to carb issues or intake leaks....JMHO....

Been chasing fuel and vac lines. Still haven't found anything[S

Thank you sarge that should be a weeks worth of checks. Lol. I will let y'all know what I find out.

 

[MercuryMac]

YBN, I've had a weird theory for a really long time so there must be some truth in it. If you have an exhaust leak near the front of the system it seems to draw a wee bit of fresh air in on deceleration and the unburnt fuel can burn in the back end of your exhaust, causing backfires. One more thing to look at, if you believe me. Good luck.

 

[Bamamav]

My 86 with a 460 did the same thing. Mine had a aftermarket Carter electric fuel pump, it finally died and I replaced it on the side of the road with one of those square cube Faucet/Purolater fuel pumps, but it still did it. Original 460 started knocking later after a carb change, so I pulled it and put in another 460, it runs fine. Pulled a head on the original 460, every piston was pock mocked like something had been in the cylinder at some time, one was beat all to hell. Funny thing, there was nothing in any of them when I pulled the heads, just the marks. All my nuts and washers from the carb swap were accounted for, so I still don't know what or when something got in there. The engine had been into before, so who knows?