[DaleO]

I'd appreciate your insight with this problem I have. I've searched through the site and figure I'm floating valves or running out of gas. Not sure what the term "lays down" actually means. I'm running a 428 with a factory intake and topped with an 800 cfm quadrajet Cliff built. Cam is an Engle 216I/226E with lifts .458I/.465E. It has a TH400 and 3.23 gears. Driving along at about 40 mph I'll nail it and it drops into second and pulls great until approaching the shifting point (~4,800 rpm) and it starts the sputtering thing. I let the gas right off and it continues to sputter for about 4 seconds and then clears up. After all this I can then continue to accelerate though I don't kick the trans down again. It just keeps accelerating in top gear. I hope I'm running out of gas and am not floating valves. Maybe there is another cause you can think of? Thank you.

[PontiacJim1959]

My opinion would be 2 things.

1.) The secondary air flap is snapping open too fast and allowing more air than fuel and for a few seconds, the air flow has to pick up fuel and then it takes off. The spring tension on th flap may need to be adjusted/tightened up just 1/4 turn and then test. If it improves but still has a little bog, go 1/4 turn more and test. Repeat if needed, but it should not need very much.

2.) The gas is spilling out of the secondary rod holes where the rods go through the top of the carb. These are not completely sealed and when accelerating real hard, gas gets sloshed back and out these holes and spills into the carb creating a rich condition until it is cleared out by being draw down into the manifold and burned off. Float leve could be too high, or even fuel pressure too high.

Simple trick that can be used to seal these holes, if it comes down to it, is to remove the carb top, lay a piece of celophane tape over the gasket/holes, install the top, and puncture holes through using the secondary rods so as to create a snug seal around the rods.

Does not sound like you are running out of fuel or when the engine power dives, it doesn't really pick up - thus "noses over" feeling and power loss. I think your RPM's are too low for valve float. So I would look into a carb issue or adjustment.

[Joe's Garage]

It wouldn't really be considered a 'bog' if it runs strong until it gets to 4,800 RPMs. That's a fuel starvation issue.

Check the fuel filter, pressure, pump, float level, etc.

Could even be a clogged screen in the tank or a leaking rubber hose between the tank and the metal line at the back.

The fact that it takes a few seconds to clear means it's NOT valves. They would clear immediately when the RPMs went down.

Good luck!

[steve25]

You need to do one or two specific test and then report back, as there are so many things that could be part of the make up of this issue and you need to let us guide you thru a process of elimination,
My first suggestion is this .
With the car warmed up accelerate hard from a slow roll in first gear and see if the motor will rev to 5200 cleanly, do not up shift .

If it does not rev clean then with the motor out of gear floor it wide open and see if it goes clean to 5200 and you are allowed to hold it at 5200 rpm for 3 seconds .
Do this at the carb with the air cleaner off so you can see and confirm that the carbs secondary’s are seen to open briefly.
If in this second test the motor will buzz clean to 5200 and let you hold it there, then you do not have a valve float condition, but this still brings up the question we need to ask which is are your valve springs still stock?

[Chris65LeMans]

Losing spark? I had an electrical issue where my engine behaves like that. I turned around to head home, and on the drive back, discovered that the problem disappeared when I turned off the heater blower.

[tooski]

I had much the same thing happen except it was a Holley on a T2. Engine would buzz wot like crazy until 5k rpm then sputter and I would let off, then it was ok. If I eased up to 5k then nailed it , it would sputter at 5400. I eased it up to 6k no problem, but wot at 5k and above was a no go. Turns out the Holley (that I've run previously) ended up being poorly adjusted (by me for engine run in). Took the carb apart, reset it properly. No problems after that. I'm fairly sure that it was dumping in too much fuel at wot.

[Kenth]

What valve springs? Can they take .465" lift w/o coil bind?
What ignition system, does it have proper voltage/current supply?
How is it adjusted initial and max at what rpm´s?
Mech or electric fuel pump, capacity and pressure?

[Cliff R]

Insufficient fuel delivery (sucking the bowl empty).

It will not be anything else as it does fine when you nail it until it reaches 4800rpm's then noses over......Cliff

[steve25]

In rereading the symptom you posted and my reply I need to ask that when the issue takes place and you let off the throttle how far does the rpm drop from the shift point of 4800?

If it drops down to even just 4000 rpm before the motor gets back to not sputtering, then I would have to rule out valve springs I think at least up to that 4800 rpm point.

One big thing fuel related wise that folks miss sometimes is that you can have a fuel line clamp a tad loose on the end of a hose on the suction side of the pump that will allow the pump to just start sucking air and little to no fuel, and yes this can take place without really seeing a fuel dripping clue happening.

[Gary H]

Originally Posted by Cliff R

Insufficient fuel delivery (sucking the bowl empty).

It will not be anything else as it does fine when you nail it until it reaches 4800rpm's then noses over......Cliff

X2! It's a fuel supply issue. Consider installing an electric pusher pump back by the fuel tank

[steve25]

Here's a simple way to prove out fuel supply issues, find yourself a big enough empty parking lot to make your drive such that the problem takes place.

when it does turn the motor off and stop the car, next get out pop the hood and remove the air cleaner and check to see if the accelerator pump is working well and if your issue is fuel supply related it will not be working well, or maybe not even at all!

[John Milner]

I'm assuming that you aren't running points but in case you are, I thought I'd mention this. I was running a set on an engine and it would sputter when you got up to around 5,000 rpm. I found that the points were causing this. I installed a Pertronix electronic module and the sputter went away and it will pull to 6,000 without an issue.

[JSchmitz]

I had a similar problem and was only getting 7 volts to the HEI. Ran a new wire and it screamed. Does sound like fuel delivery though.

[DaleO]

Originally Posted by Kenth

What valve springs? Can they take .465" lift w/o coil bind?
What ignition system, does it have proper voltage/current supply?
How is it adjusted initial and max at what rpm´s?
Mech or electric fuel pump, capacity and pressure?

The heads are 6X-4 which were built by Dave Bisschop for 240cfm. They're good for .550".
I have HEI off a 12V source but will verify. Full advance is 34 degrees and initial is at 12 degrees.
I have a stock mechanical pump with 3/8 inch all the way tank to carb. The tank and pickup are new as are the short segments of rubber tying the metal sections together. Return line is off the pump. The pump is rated at 40gpm but who knows. I don't have a pressure gauge to check with, at least not yet.

thanks for your input.

[DaleO]

Originally Posted by steve25

You need to do one or two specific test and then report back, as there are so many things that could be part of the make up of this issue and you need to let us guide you thru a process of elimination,
My first suggestion is this .
With the car warmed up accelerate hard from a slow roll in first gear and see if the motor will rev to 5200 cleanly, do not up shift .

If it does not rev clean then with the motor out of gear floor it wide open and see if it goes clean to 5200 and you are allowed to hold it at 5200 rpm for 3 seconds .
Do this at the carb with the air cleaner off so you can see and confirm that the carbs secondary’s are seen to open briefly.
If in this second test the motor will buzz clean to 5200 and let you hold it there, then you do not have a valve float condition, but this still brings up the question we need to ask which is are your valve springs still stock?

I will do this once the car is running again. It's presently on the rack getting a fresh TH400 and new TSP 9.5 installed. Also struggling through getting my identify fraud issue fixed so that is priority...but i appreciate this escape. The heads have been built by Dave Bisschop and are good for .550 inch.

[DaleO]

Thanks for all you replies everyone. I'll work my way through the checklist but I'm starting with the fuel diagnosis as that seems the likely culprit. Over time I've installed a new tank with new sending unit and sock. I have replaced the rubber lines between the steel lines. The pump is new though it is a factory equivalent. The whole fuel system is 3/8 inch and right now I'm guessing it will end up being 1/2 inch with a pusher by the time this is all figured out.

Something that nags me a bit is did the 405 horse 421 Super Duties have a regular pump? I guess I'm assuming they did. Same question for the 455 SD? I can't be making that kind of power, Any thoughts on that?

[steve25]

Well your heads then should not be a issue valve spring wise, and a 3/8” fuel system should serve you just fine ( assuming the tank pickup is also up sized ) since the greatest level of Hp you could possibly make with 240 cfm heads is 490 hp, but that would take a far bigger Cam then you are currently running anyway!

Is your HEI new or used?

Another possibility for crappy running is if you have the super light ( most times silver colored ) advance springs in the HEI as they don’t even work right with very light advance weights , not less heavy stock ones!

[Half-Inch Stud]

What brand electric fuel pump do you got?

[JSchmitz]

Be sure and check the supplied distributor voltage with the car running. Mine had 12 volts static and 7 volts running.

[78w72]

Originally Posted by Half-Inch Stud

What brand electric fuel pump do you got?

factory equivalent mech pump...