Need advice, 70 Mustang 428SCJ

[Vegas69]

It has to be losing fuel or spark unless the exhaust is clogged? I've seen it on modern cars where the cats will close up. Muffler batting? If that's not it, I'd swap the carb. It may have an internal clog in the primary circuit. Also, you may see a spark, but is it strong enough to jump the gap and still on every cylinder? Have you checked the coils resistance?

[Solid LT1]

Describe the motor problem a little better......a quick die off would probably be electrical related.......stumbling before die off would be fuel. If there is any backfire.....could get into things like weak valve springs.

[Musclerodz]

Originally Posted by Solid LT1

Describe the motor problem a little better......a quick die off would probably be electrical related.......stumbling before die off would be fuel. If there is any backfire.....could get into things like weak valve springs.

Already been into the heads. Had a vibration at idle I could not get out of it and found two cylinders that the valve were being held off the seat just enough to cause dead cylinder. Went through the heads and double checked everything there. I'm pretty certain its a fuel issue, just one I have yet to find.

[Vegas69]

Pull a plug to see if it's wet or dry when it dies.

[Solid LT1]

I'm thinking about one other thing.....being a SCJ its a 4 speed car right? Is the factory rev limiter box still hooked up in the ignition circuit? My 1st car was a 70 Boss302 Eliminator and I went through some tribulations troubleshooting a miss that was finally diagnosed to the magic little box on the drivers fender. The box should be bypassed if its present.

[dale68z]

o this problem happened after cylinder head replacement? What was holding the valve off the seat?

Can you clarify this from post 1.

"It will restart on prime but won't stay running"
Are you pouring fuel into the carb, where?

Does it just shut off?

where is the fuel pressure gauge installed?

[Musclerodz]

Originally Posted by dale68z

o this problem happened after cylinder head replacement? What was holding the valve off the seat?

Can you clarify this from post 1.

"It will restart on prime but won't stay running"
Are you pouring fuel into the carb, where?

Does it just shut off?

where is the fuel pressure gauge installed?

Didnt replace heads, they are original to car, only repaired the problem, the valve was being held off the seat. Problem was there before.

When it restarts it sometimes will stay running as long as no load on it. Other times it restarts like I just primed the carb and then dies.

pressure gauge was tapped into system just before carb.

[Musclerodz]

Originally Posted by Solid LT1

I'm thinking about one other thing.....being a SCJ its a 4 speed car right? Is the factory rev limiter box still hooked up in the ignition circuit? My 1st car was a 70 Boss302 Eliminator and I went through some tribulations troubleshooting a miss that was finally diagnosed to the magic little box on the drivers fender. The box should be bypassed if its present.

Already bypassed it, no change

[Musclerodz]

Originally Posted by Vegas69

It has to be losing fuel or spark unless the exhaust is clogged? I've seen it on modern cars where the cats will close up. Muffler batting? If that's not it, I'd swap the carb. It may have an internal clog in the primary circuit. Also, you may see a spark, but is it strong enough to jump the gap and still on every cylinder? Have you checked the coils resistance?

I starting to think its the floats hanging up or needle and seat issue. Its a brand new Holley, and I have adjusted everything to where its properly adjusted and purrs like a kitten in the shop, but the last couple times I have drove it now, it shuts down right after I stand on it like it running out of fuel. Whats driving me nuts is not the consistent failure, its the inconsistent way it shuts down.

Just swapped the coil, no change.