My 351 Crate Motor has a miss

[rbray]

Hi Guys,
I am hoping someone can help me sort out a problem I'm having with my motor.
I have a new 351 FMS crate motor that has a miss.
When we first started the motor we used a rebuilt Holley carb with the following results:
at idle there was a steady miss at about 700 rpm.
when rpms were brought up slowly to 2000 the engine developed a sever stumble.

A friend loaned me his Carter carb and after we switched out the Holley the miss and the stumble went away.
What has me puzzled is the stumbled and miss has returned while still using the Carter. No other changes have been made.

I also noticed some strange readings on my SW tach. At idle the rpms indicated on the tach jump around from 700 to about 2000 with no apparent change in engine sound. I'm using an MSD 6AL ..
I'm wondering it this has something to do with my other problems.

Any help would be appreciated.

[Back in Black]

You may have surmised this, but it sounds like an ignition/and or electrical problem. Do you have the computerized MSD ignition? Maybe it was fried or defective ? Maybe there is a crossed wire in the build? (I am assuming for the moment that this is a new build)

The problem mat have been compounded by the first carb ? But maybe you have half/fried a wire/the computer, in the meantime, so it came back?

If it was mechanical, the problem would have been constant ?


Just guesses, maybe someone else recognizes the exact problemo and can help

By the way, I never rebuild carbs, I buy quality rebuilt carbs and just drop the puppy on the motor. Did I mention I HATE carbs? My dad can rebuild them in his sleep, I HATE them

[Curt C.]

Yes, check your wiring on the ignition in the steering column, ignition box etc. I saw my tach jump around like yours too. Turned out to be a burned pig tail plug in the column ignition.

Curt

[boxhead]

Sounds to me like it is an ignition fault.
I would check all wire terminals as Curt described.