Motor breaking up...making me nuts!

So here's the deal. I have a bad ass 347 in the Mav and it wants to go..haaaaa...but for the life of me, I can find a high rpm miss.

Here's the rundwown.....

347 Stroker
All forged internals
AFR 205 heads (58cc chambers)
Port matched Vic Jr.
Ford Z cam
1.6 Scorpion Roller Rockers
Holley 750
Ford Racing 9mm wires
Ford DuraSpark Box
MSD Pro Billet Dizzy. No vac advance
1 5/8 Long tube headers
4.11 Spool
Built C4 w/4500 Stall
Cheetah Turbo Shifter

The damn thing will run great, all the way to about 6k, if you ease into the throttle but if you mat it, once it gets to about 4.5k, it breaks ups bad and pops out the exhaust. I have tried all kinds of things so far.

1. Played with the timing from 12 to 16 degrees initial.
2. Changed from Factory Ford Dizzy to MSD Pro Billet.
3. Re-stabbed the dizzy a few times to make sure it was right.
4. Made sure valves were adjusted properly. Checked compression and header temps.

I'm 35 so I'm kind of a "tweener" as far as carb and efi stuff. I'll readily admit that I can build a motor but carbs are not my strong suit. Any help would be greatly appreciated. I know when this thing is right, it's gonna be fast as hell!!! Thanks guys!

 

Bad coil/poor fuel delivery (not enough fuel) Running too lean...Whats your total timing set at...Initial may be good but...Centrifugal may not be coming soon enough.

 

Go make a full pass, then pull the plugs. See what they tell you.

 

The way this thing is running I wouldn't even bother with a full pass.

 

I second the bad coil.

Cleaver

 

I know the coil is good. I left the coil wire off and it was shooting a spark out the top! Haaaaa...... I was thinking fuel delivery as well. I would think a 750 would be enough but who know. Oh...I also have the FPR set at 7.5 lbs. everything I've read says that's good fuel pressure.

 

howdy. Total timing should be in by 2800 rpm. About 32-36 total. try 32, then 30 and see what the engine likes.Your 750, is a vac secondary or a double pumper.If vac, then maybe that isn,t allowing secondaries to open, there fore the engine is only runnin on the front primaries. A 2 barrel effect.So at so acceleration, the carb can keep up, but anything else and the engine nis starving for fuel. try these. JMO Ron

 

I'd say it's your Dura-crap box. I hate those things. Old & outdated.

 

Yeah....I was suspect of the DuraSpark box as well. I need to get a 6al. Oh yeah....the carb is a double pumper.

 

the 750 is too big but shouldnt cause the problem on the top end.
are the springs in your head the right ones for the cam and lifters. a hydraulic lifter is really heavy and on a decent size cam and requires alot of spring pressure.

 

Jetting a big carb down won't make it pull less air - it will just be lean - get the right size carb (that is not likely your problem at high rpm).

Ignition, valve springs?, fuel pressure at WOT at the carb may be low. That is a fuel delivery problem.

 

Please explain how using smaller jets in a 750 equates to using a smaller (650 cfm) carb?

Also, how did you determine that a 750 cfm carb is too big for this engine?

I am hoping to learn something here. I may be able to get my car into the 10's by removing the 750 I am using on my 347 to run 11.50. I just don't want to spend the money before understanding why.

Thanks.

 

Yeah...I'm confused as well. A stroker has a lot of piston speed and can pull a ton of air. Also, Ford put a 780 Holley on the original BOSS 302. Just wondering why a 750 would be too big?

 

The 750 is a starting point on a stout 347, Ive tried many dura spark boxes and personally have never seen one that would run past 5500, I would recomend an MSD 6AL box, you wont believe how much better it will run.

 

Yeah....I think a 6al is in order. Even if it turns out that it's not that, the 6al is still a good upgrade.