Hey all, I'm having this problem at high rpm's with my 406. When I floor it, and reach around 5000 rpm or so, the car starts to hesitate, sputter, and bog, and I have to let off the accelerator. Then I can smell raw fuel as if its running way too rich, and when I go to get back on the throttle the car hesitates a little and goes back to normal, unless I floor it again. I have done my timing; 36* and carb adjustments. I'm starting to think that the carb is sending too much fuel to the motor and it's causing the plugs to flood, which causes the sputtering and the poor recovery from the hard accelaration. The carb is a Holley 4010 750 that came with the motor, might the carb need a rebuild? What should I look for? Anyways, here are the specs on my motor:
400 bored .030 over
882 heads 1.94/1.50 valves
Performer intake manifold with 1" spacer
HEI ignition
Holley 750
I think it has around a 218/218 at .050 cam with around .460/.470 lift
The motor is very responsive and has a lot of torque, but for some reason it's having this problem at high rpm's and its not a good feeling. What could be causing this?!? I have no idea what kind of jets are in the carb, maybe I need to put smaller ones in?
Thanks for all the help,
-Cyrus

I would go to mortec .com and find the stock jetting for your carb. IMHO the carb should be a good fit for your combo. I experienced a problem like what your describing with my 396 bored 60 over and it turned out to be valve springs. I would start with spring heights and open and seat pressure of your valve springs. just my .02 cents

3nine6

What type fuel pump are you running? Do you have a fuel pressure gauge? It might sound strange but if the motor is laying over at 5000 rpm it may not be getting enough fuel. Just a thought.

David

I checked mortec and it said that stock jetting is something like 73F and 75, no idea if this is alright for my setup or not? I know that I need to readjust my valves as I hear a slight ticking coming from the rocker, I adjusted it when it was on the stand, and now after a coupla miles I need to readjust them, could that be causing the problem, like the valve adjustment being out of whack and causing it to do this? How would I go about checking the valve springs like you mentioned?
Thanks,
-Cyrus

It has a Chrome Holley fuel pump. 7.5 psi shutoff pressure, flows up to 80 gallons per hour. Bought it from PAW and these specs are straight out of the catalog. What do you guys think? I hope it's nothing serious.
-Cyrus

You need to find out the spec's for your springs and cam. They need to be insatalled at a certain height so #1 they don't coil bind when under load. #2 That they meet the open and seat #'s of presure for the cams needs. Coil bind and incorect spring heights IMHO are the main reasons for the problem you are describing.A local machine shop could check spring pressure at installed spring height (for a minimal cost )to be sure they meet your cams spec's. hopefully you still have your cam and spring spec cards or can find out. As for your carb i would stock jet it and adjust from there. Stock jetting for the 750 cfm is pretty close for the your comb if you jet up jet up the rear first.also your pump should be good for your comb. Again just my.02 cents.
3nine6