347 problems

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

Try posting this question in the general forums section. You'll get some responses to your inquiry.

I have thought about why it would misfire. It can only be the things. A engine needs 3 things to operate. 1) Compression 2) fuel and 3rd) Spark. So where is the problem? Compression is obviously not the issue, It sounds like the spark is flying and you have checked the timing/.electrical and there are no loose connections to cause a miss. The plugs are OK, Assuming you have checked them. If there is allot of unburnt gas you will see the gray/ tan flaky build up on the electrodes. I am guessing at something here but it my make sense. The Parker funnel Web is a good manifold but is what I call full throttle manifold. I mean It works better under full race applications, wide open throttle with the correct parts to make a good fuel air mixture. I know the designer and maker of the Funnel Web. It sounds like you may have a mismatch on the parts combo. You would need allot of fuel to make the funnel web work well. The cam grind needs to be large. likely up in the .550 or better, with heads to support the air flow. The carb for such a combo would be better than a 770cfm.
You have to have allot of velocity through this manifold to make it work right. The 770 may restrict the air needed to cause the right pressure to happen and continue to the combustion chamber.You may be missing due to the air fuel mixture separating and ending up in the combustion chamber as mosty gas, and unable to burn properly. I think that changing the funnel web to an Edelbrock air gap manifold might be a good call. This is what I see happening. You start out with a 770 CFM carb that is trying to supply a manifold that needs much more cfm to work right. The air fuel velocity dies when it hits the funnel web. This causes a stall at this point. What happens next? The fuel/airwill serrate and depending if it can bet going again may get going and then slow down again. This is the worse situation you can have. Lose of velocity is lose of energy, which is then taken from another place to get it going again. By the time it get the chamber it is weak and make for a bad burn in the chamber. Knowing what you have said this could the problem, air fuel that is just not as burnable as it could be or has to be. It may be something simple like a bad connection in the wiring. Check the plug wire, and that the advance is working on the distributor. Is the Avenger mechanical or vacuum secondaries? If mechanical the check adjustments on linkage to accelerator pumps to see that you are not getting to much fuel to early when pressing throttle. these are just ideas and things to check. It can be something way different. I hope you can get it where you want it and where you deserve it to be.Sounds like allot of hard work. Do Not get discouraged. This is the reality of the hobby.
Best wishes Paul

First lets assume that cam matches the funnel web. Do you know the specs of the cam? What heads are on the engine... any vital specs??? If the cam is a radical cam that matches the funnel web then:


That is not the right carb for your application. You need a race calibrated carb. A race carb has much richer Idle Fuel circuit/transfer slot circuit, different air-bleeds, and different calibration. I would bet that before the engine was sold, someone switched carbs from the one they were using.

Other things to consider.

Fuel pressure is very important. Too much and you will not get it to idle for crap. To little, it will run out of gas before the 1/4 mile. A fuel regulator is very important as well as fuel pump capacity.

Initial timing is also important. If your trying to run that engine at 15 BTDC, you will never get it to run. 20 - 25 d BTDC is what is needed in a race engine.

Only more information will let us help you. Without it, it is only guessing.

The most common problem is fouled spark plugs. Even if they are brand new, once they are fouled, they must be replaced before you can move forward. The biggest thing that can cause plug fouling is cold startup with SLOW ideling, These are death on plugs, even when everything is in perfect order.The biggest thing that lets a plug foul is too cold of a heat rangr. You should have the hottest heat range of plug you can find, if you have a big cam and expect it to idle at all.

JOE SHERMAN RACING ENGINES

Big Joe is right. I replaced my plugs a few years back and started messing with carbs. It started backfiring so I went back to the 570 Holley. Too late, my plugs were already fouled. But since I figured they were new I spent several days messing with wires and ignition. The last thing I did was check to see that my new plugs were fouled. I changed them out and she purred like a tiger.

well first off specs on it, it's a custom ground EFI cam from Erson cams. it is a radical cam, the lift is around 550, probably more. it has a set of roush windsor heads. i re-built the carb on it a couple times, still miss-fired. had a 6al box on it, worked alright for just warming it up but on the track it would miss-fire at about 4000 rpms. the motor it self is capable and has power to 7500rpms. plugs have been changed several times, and are carboned but they all smell like gas. the timing issue is what's really confusing because i was running 20 initial into it, when the problems started i could advance the timing with no change and retard the timing with no change at all. all the 6al box did was just change when it was doing it from off idle to about 4000 like i said. thanks for all the help though, still chasing that deamon

That sounds like a carb that is going lean to me at High RPM's.

If you rebuilt the carb, do you know what the jet settings for the front and rear are?

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

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