myseterous stumble/miss from 1200 to 1700rpm

[FullSizeJeeper]

Just turned 500 miles and I'm starting to give this motor a little more throttle, but still not purring like I want. It's a 74 AMC 360, .040 over, stock pistons, summit 8600 cam, crane roller rockers, summit digital ignition, MSD disributor and coil. Edelbock preformer intake, timing chain, ceramic headers, and 600 carb. Port and polished intake, +.10 pushrods to correct value geometery. I have plated off the EGR and have the carb dailed in.

Intital timing is at 10* BTDC, total is 35* BTDC. Running 14"hg vacuum at 700 RPM in drive, but do have a 1 to 1.5" flux on the vacuum gauge. Did another comp test over weekend came up with: 1 144
2 143
3 143
4 180
5 144
6 140
7 145
8 170

The biggist issue right now is missing at 1200 to 1500 rpms. It shows up when you give a slight throttle from a coast. Once you get into the 1700-2000rpms it cleans up. If you give it a slight throttle at idle, you can watch the vacuum adv arm start moving in and out when the stumbling/missing starts. If you pull and plug the vacuum advance line from the carb it cleans up.

I have direct ported vacuum to the dizzy. Any idea what is going on here?

[jeepsr4ever]

Where are you pulling the vaccum from?

[tufcj]

I would say check vacuum and mechanical advance. Sounds like you're bringing in too much advance too fast. Make sure the vacuum source is ported, and not manifold vacuum.

Another thought - What is your initial timing, and you are setting it with the vacuum disconnected?

Bob
tufcj

[FullSizeJeeper]

The dizzy is hooked directly to the ported vacuum (passenger side of edelbrock 1405, bypassed CTO). The initial timing is 10* BTDC, set at 700rpm in drive with the vacuum advanced diconnected and plugged.

The problem seems to be with the vacuum advance trying to kick in early, I agree. I believe the problem is the vacuum advance is kicking in and out in this RPM range rather than a steady pull.

What would cause this?

[ironman_gq]

you can get an adjustable vacuum advance or disconnect it and see if it helps.