347 problems

I don't know the Avenger Carb very well, but from experiance, you are very small on your jet sizes.

Atleast 74 - 76 in the front and at least 80 - 86 in the rear is needed.

You may have 2 different issues causing the same skip, being too lean like you are now... Having cold plugs could be a second issue. you are slowly melting your pistons. Take a plug out, and take some really close-up photos of it for us. Few different angles. Post them when you can.

Originally Posted by BIGJOE

People do NOT want to hear this, but almost ALL vacuum carbs DO NOT OPen all the way, On the dyno. a double pumper will alway make 15 to 25 MORE HP since the vacuum carb is not openong fully. If your are still fouling plugs, the heat range is TOO COLD for your type of driving. You should get the HOTTEST heat range you can find, and MAYBE, you will get thru this, It is all going to come down to your carburetor. SOMETHING is WRONG with it. You should replace it with a known carb that works well on another engine.

JOE SHERMAN RACING ENGINES

Been there, done that.

Originally Posted by 347Maverick

it has 70 fronts 72 rear at the moment, it's had up to 82 front 84 rear with no change in the mis-firing between the jets...i know vaccum carbs aren't quite as good but the street avengers are good carbs from everything i've seen, but they do open fine

Yup...thats small. My 770 SA on a 331 was professionally tuned with 72s and 80s as I recall. My 750 DP was professionally tuned with 71s and 82s (or 83s...can't remember for sure). Both worked great although the 770 SA was selected for the car when I had a C4 and it would never open fully on the Secondary side for whatever reason despite light spring, opened up orifice (maybe the carb was too big for the engine). Migrated to a T5z and single plane and changed to a 750 DP and have never looked back.

I'm having the same problem with my 342 right now. It also has a funnel Web, but I think I'm going to try the spqark plugs first.

I run a Funnel Web (real one) and dont have this issue.
ONE thing to think of. If you have the MSD box on the car and recently put it on and have this problem, There ARE some boxes from the factory that have the purple and green wire to the dist, wired backwards. If you use the pick up from the dist and wire it like the manual says sometimes it is wrong and throws things way out of wack.
Correct me if I am wrong Joe or someone but the correct orientation is wired they way that gives you the most jump in advance when the wires are switched from the way it is running now.
We suffered at a race in Georgia from this and found it out thankfully before running the heat race.

I am having kind of the same problem. just at idle is fine. When you start to step on it, it stubbles and starts to get better as the rpm increases. But still not right. I'm going to try a set of plugs. If that dosn't do it, good bye funel Web. The only differents between mine and yours is my came is 575 lift, and I have an AEM 750 holley double pumper. I should have tried the Funnel Web intake with my old motor.

I have a 347 with afr185's, trick flow stage 3 cam(575/595) funnelweb and a 650dp. If I remeber right I have 73/82 jets and it runs great. I do not think the funnel web is your problem.

Originally Posted by 347Maverick

I have a roller 347 stroker, out of an 89 HO mustang block. the cam is ground for an EFI or carburator. it currently has a Parker Funnel Web intake manifold on it, with a 770cfm street avenger carburator. the ignition system is a mallory unelite destributor, and pro-coil. the problem is that the car wont tune at all. i've put a new distributor in it, timed it repeatedly. it's only made one decent pass down the 1/4 mile but then the very next day when i started it up, it was miss-firing and i've run out of things to try. if anyone has any idea what could be going on, anyhelp keeping the car on the road would be appriciated

I was having problems too. This is how I cured mine. I set my initial timing to 20 deg
min. with total 36. It helped me get more signal to the Carb. I went from a 4.5 power valve to a 6.5. I had to richen up my idle mixtures to 2 turns primary and 13/4 turns on the secondary. I am running an AEM Holley HP 750. I called Aem and they were really helpful. A little extra initial timing seemed to make it tuneable.
I'm going to change the idle bleeds, that will get my screws in a little further where they should be. Now that it's working, I very impressed and happy. I hope some of this helps someone in some way. The only other thing I heard, some guys are having intake gasket leaks with there fake made in china copy cat intakes. The angles is supposed to be off, and there leaking internally. Again that's what I heard never witnessed anything.
Thanks for all the great people an info on this site.
John

HI, make sure your electrical system is up to par, this could be the cause.
Frank

When I first installed the intake on the new engine, I almost took it off. I had a few problem's, and I was blaming the intake for everything. Now that I finally dialed in everything, I found it to be as streetable as a Victor Junior. One thing that did happen at the race track is, it started blowing oil from the top end. After changing the rocker gaskets and driving my self crazy, I noticed a hole at the front of the intake. It turned out that a frost plug type what ever you call it, blew out on the front of the intaske manifold. Mine has 2 plug's on the front, has any one else had problems with these? or know what there for. As far as performance goes, in time everyone will be running them. They make more power, and that's reason enough.
Thanks
John