runs, but doesn't run....

[zipzip]

I have a perplexing problem....

I've run the engine for about 1/2 hour total. It will stay running if I put in the 3000 rpm rev limit chip in the MSD ignition (6AL). If I replace the chip with the 6000 rpm chip, it will start, but not stay running, even if I goose the carb.

I think it may have something to do with an improper carb setup (I got the thing used and don't know where it's set at), but before I tear into it, I'd like your thoughts.

Here's some specs:

-302 engine - pretty much stock but with GT40P heads, and a "slightly" bumped cam - Intake .448 & 204° duration, Exhaust .472 & 214° duration
-Duraspark ignition - 8° initial advance, about 40° total (with vacuum line on)
-Holley 4160 600 cfm, vacuum secondaries, manual choke.
-Weiand 8011 intake, dual plane

I've messed with the idle adjust screws - anywhere from all the way in to 1-1/2 turns out with no change in operation. It will idle up at the rev limit and I can't get it to drop down.

I've read that sometimes a small hole has to be drilled in the butterflies to get idle adjustment to work. What about that?

It smells rich, but the plugs are ok - It's probably because the ignition is cutting the spark at the rev limit.

What to check? What could it be?

[Richard Hudgins]

ZipZip,

You question and explaination are quite confusing.

You state that the engine will run with the 3k chip, but not with the 6k chip. This indicates a bad chip. (I have seen quite a few of these.)

But then you say "It will idle up at the rev limit and I can't get it to drop down. (SNIP)It's probably because the ignition is cutting the spark at the rev limit.

Will the engine run to 6k? Idle up to rev limit? (That is one hell of a idle.)

Can you please explain a bit further the symptoms.

[427 S/O]

Go chipless and see what happens....

[zipzip]

Sorry for the confusion - I'll restate it:

If I put the 6000 chip in, it will start and run for a max of about 30 seconds then die. If I goose the throttle, it will respond, but not stay going. If I play with the choke, same result. The "idle" is somewhere around 3500-4000 (guess).

With the 3000 chip, it will start and run continuously, but will not come down off of the rev limit.

[trularin]

bad box or chip.

[Edbo]

I see in the photo that you have the ignition box mounted remotely from the engine. Are you sure you have a good ground to the engine? With a heavy gauge wire?

Ed

[kdavies3]

Are you sure that the throttle butterflys are closing ?
It sounds to me like you may have a large air leak. between carb and manifolld or manifold and block/ heads.
This would explain the lack of idle below 3000 rpm.

[Mr.Fixit]

You say you have a duraspark ignition, and an MSD. I see the MSD in the photo, run it without a chip in the rev limiter. With the cam you stated, you will not need to drill your throttle blades, that is required only with big duration cams that do not develop vacuum very well. If the difference between running and not running is determined by the rev limiter chip, what makes you think there is a carb problem? I would think it is ignition. You don't need vacuum advance for a cobra, I would disconnect the hose and plug the ports..

[zipzip]

I'm going after the carb because of the idle issue. Can there be a high idle situation if it is an electrical problem?

Mr. Fixit - just curious - why is there no need for the vacuum advance? Also, a typo on the duraspark - it the distributor, not ignition box. Sorry.

Should the MSD box still trigger the coil if the "small" red 12v wire was disconnected? The only way I've been able to shut the engine off is by grounding the white wire.

I'll be trying it with no chip soon - thanks for all the assistance!

Todd