Manipulating the firing order?

[myrtle]

(kind of a long read, sorry)

So I have had a hard time getting my car dialed in,she idles fine, but it stutters horribly all the way through the RPM range and just gave her a complete tune up. New spark plugs, distributor, wires etc, the whole sha'bang. The only thing I can think of is a bad carb? and its either surging or just worthless when it comes to fuel distribution. It smells extremely rich and feels like it has either a severely bad timing issue or horribly fouled up plugs (idle timing i think was 12 degrees on the light and 15 degrees via vacuum). I just bought the car and the previous owner had no idea as to the mods on the car,..

Currently has a 650 Holley, I can see Crane Cam roller rockers when I pull the breather cap electronic points ignition upgrade and an after-market Edelbrock intake,.. sorry I dont know which one.

My question is,.. how can I tell if I have an aftermarket cam? Its hard to tell from the idle because it has such a horrible exhaust setup with those cheapo turbo mufflers along with bad piping. I have a complete header back setup coming in tomorrow or the day after, so that should help me in telling weather or not it has a mild cam at the very least,.. which is what Im assuming because it has adjustable roller rockers,..??

Now with that,.. I came to this conclusion that may be a little irrational,. I was reading an older Mopar Action magazine today and they spoke about an engine build that had a particular camshaft that called for cylinders 4 & 7 to be swapped in the firing order,..? Is it possible that I probably have such a cam shaft and the previous owner had no idea and time it according to a stock firing order,..?


Any and all help is greatly appreciated, let me know if there is anything else I could provide to help diagnose my issue.

[71chally416]

Not on a Mope. I believe some ford motor(s) can use different cams to change the firing order.

Have you done a compression test?

[myrtle]

No I have not done a compression test. That was next on the list along with a leak-down and smoke test after a carb swap/rebuild weekend.

For whatever its worth,.. I was referring to the Current (April 2009) issue of Mopar Muscle. On pages 16 & 22 they address the technique I was asking about.

[71chally416]

You would have two cylinders dead missing at idle if that was the (unlikely) case and it would be noticably running rough. Sounds like you might have a high speed circuit problem with your carb if it idles OK. Have another one you can swap on? If not disassemble it, clean it good with carb cleaner and air pressure and don't forget the air bleeds. 

[bb71challenger]

You might want to pull the valve covers and check the roller rockers. I have Crane gold rockers and even though I thought I had them tight they were still horrible for backing off to the point that during cam break in a nut actually came all the way off the adjuster. It might be as simple as that. Bad thing is you might have a couple of adjuster nuts floating around in the crank case. Hope its an easy fix whatever it is, good luck.

[Changin Gears]

On a list of 100 things that might cause the rough running I would list a 4 -7 swap cam about #98 just above a meteor stuck in the carb.  I agree with 71chally, swap the carb if you can.

[myrtle]

Sounds good. I tried it and it ran like ****, so yeah so much for that.

Well, guess I will start digging around for a carb.

[71chally416]

Yeah, I would have bet the farm the firing order wasn't the problem. 

[Aussie Challenger]

  Have you checked the coil? Low output coils will idle but perform badly. A simple way is to check the spark color and strength, color should be blue and create a thick spark at least 1/4" long. A quick easy test, then maybe onto carby.   

[myrtle]

  Have you checked the coil? Low output coils will idle but perform badly. A simple way is to check the spark color and strength, color should be blue and create a thick spark at least 1/4" long. A quick easy test, then maybe onto carby.   

Well I just picked up a demon 750 last night, so I will do the wires, coil and Carb all at once and hope for the best.

[MEK-Dangerfield]

Good luck with the new demon.  I have known people to send them back before they even install them.   

[Old MrB]

Now I'm far from an expert but here's my    I've had engines run fine at idle but not accelerate due to a bad timing belt install.  Is it possible that the engine's timing chain has jumped a tooth?  I've got far more experience on asian imports but surely there's a way to see if the cam is in proper time with the crank.   

[mopar12372]

possible blown power valve in carb (known to holleys with out check ball)  ,  accelerator pump  mis adjusted  or rotton .

 if you have a mechanical fuel pump gone  bad .  rocker arms installed wrong .  could be many things , my sugetsion . start with the small stuff and work your way up / good luck with that new carb .