440 runs perfect for 5 seconds, then starts missing. Every time. Help.

[TASummers]

High compression & low octane gas?

10:1. It runs well in premium.

 

[Geoff 2]

Sounds like flooding. Check needle/seats & replace met block gaskets.

 

[diesel_lv]

You initially replaced a wire n plugs. Have you verified since then which cylinders are dropping? A spay bottle on the header at each exhaust port or a digital temp gun. Verify if cylinders are running cooler. Is it the same ones each time?

 

[PRHeads]

Here’s what I’d try to help determine if it’s a fuel control issue……

Have a flash light handy and remove the air filter assy.

Start the engine and let it settle in to it’s running rough condition.
While it’s misbehaving during idle(throttle closed), shine the flashlight down the carb and see if there is any fuel dribbling out of the boosters. Look at all 4.

If you see any fuel coming from the boosters there is a float control issue, or they’re set too high.

In carbs that routinely sit for long periods of time it’s not unusual for the needle & seat o-rings to get hard or shrink, and then allow fuel to pass thru.

 

[Nxcoupe]

Here’s what I’d try to help determine if it’s a fuel control issue……

Have a flash light handy and remove the air filter assy.

Start the engine and let it settle in to it’s running rough condition.
While it’s misbehaving during idle(throttle closed), shine the flashlight down the carb and see if there is any fuel dribbling out of the boosters. Look at all 4.

If you see any fuel coming from the boosters there is a float control issue, or they’re set too high.

In carbs that routinely sit for long periods of time it’s not unusual for the needle & seat o-rings to get hard or shrink, and then allow fuel to pass thru.

I like this, along with crud building up in the metering block orifices.

 

[B-Body 70]

I had this problem once on my daughters 85 Audi 5 cylinder took me awhile to find the intermittent misfire. It was a broken valve spring rotating just right.

 

[Don Gould]

I wonder if your carb is flooding out into the engine. Your AFR suggests that as a possibility. Have you checked your float levels? But a greater possibility may be a leaky needle and seat. A high fuel level in the bowl will syphon down somewhat when you kill the engine. And the as you refries it, it runs OK until the bowl overfills by the leaky needle/seat and floods the engine?

Just some wild guesses. But I seriously would have someone start the car while you watch the bowl levels (assuming your Quick Fuel carb has glass sight ports in the bowls) to see if the fuel rises over the sight glass. And also to look down the throats to watch for signs of gas running out the boosters.

I'm with AR67, Take off the Air Cleaner, look in the carb, watch the booster for dripping fuel. At idle there should be no fuel dripping from the booster.
Check the float levels, make sure your Idle Air Bleeds are not plugged (the outer ones)
Pull the plugs and look for the anomaly it show as black and sooty or wet with raw fuel.

 

[Sixpactogo]

It sounds electrical to me..........I would replace the rest of the plug wires. I believe you have one of them that fires a couple times until it gets saturated, then fails.

 

[EARLY B]

* 440/508 with Solid cam. Quick Fuel 950 Race. FBO Ignition Module. Firecore Distributor and Wires. New Plugs. *

I drove my car to work a while ago. On the way home, it was running fine. I stopped at the light, and felt like I lost a cylinder. My air fuel ratio went from 12.5:1 down to 10:1. I thought I must’ve burned to a plug wire. Drove it home on 7. Did find a suspect wire, and changed it, along with all spark plugs. No change.

* * When I crank the engine, it runs clean for 5-10 seconds, then starts missing (like a running on 6 or 7). IT DOES THIS EVERY TIME. Turn it off, fire it up, clean for 5-10, then rough.

AFR drops from 12-13 to 10.

I’ve checked every ground, and added grounds. I can’t find any arcing wires. Distributor cap “looks good”. I called 4 Seconds Flat and they suggested I cycle the rev limiter. No change. I’ve got 14.5 volts from the alt.

The fact that I can repeat this “ clean to rough” cycle over and over is what’s bugging me.

What do y'all think?

View attachment 1668239

Valve adjustment tooo tight

 

[TASummers]

SOLVED:

Thanks for all the insight guys (and sorry it took me so long to get back). Found that rear bowl was flooding within 10 seconds of run time. Pulled bowls - blue gaskets on both sides of the metering blocks had starting coming apart, leaving trash. Cleaned bowls/jets/everything and reassembled with new gaskets. Same Issue. Replaced rear needle/seat & o-ring. Problem solved.

 

[oldkimmer]

Glad u got it fixed. Kim