great info, what causes a surge at idle in gear but idles in park great?

 

A stock motor will cruise at a high engine vacuum - maybe 17" or so? At idle maybe 19-21 - if you subtract 2 from 17..
there is no 15 PV; racing motors otoh may top out at 9" or 10" Hg, the problem there is a PV may open at idle or flutter. Most peeps will want to use the divide by 2 method.

Set your timing first, then adjust (wheels chocked, emergency brake on, from the side or in reverse even) idle and idle mixture, in gear.

If the vacuum advance is connected to manifold vacuum it may be difficult to obtain a steady idle with an automatic.

 

I didn't make it to the performance shop today but pulled a pump cam and squirter off a spare 600 I have. Changed out my red cam for an Orange one and it was worse. Swapped back to red and changed the squirter from 25 to 31 and it didn't help either. I know I need to still get a cam variety kit and different squirters that are 1-2 bigger instead of 6.

I leaned up down a hair to 1.25 turns out and it seemed to like it. Even bumped the the vacuum up to 20 in park and 16 in gear.

 

Also, I took it for a test run and it runs way better under WOT but still has the stumble off idle.

 

If you tune this thing in gear at least do it close to a tree and yourself to the side. I woulnt do it that way period but I suppose it could be done with a helping foot on the brakes..

My situations a bit different but I was putting headers in a automatic bronco and knocked the gear rod out of park.. That damn thing drug me about 20 feet (unscaved) before it hear a tree "rearward".. One getting out of control is just a chance I dont play anymore

 

I always have a buddy, neighbor, or even my ol lady to hop in and hold the brakes. If I ever did it by myself it would be up against a tree. Even with wheel chocks the 38's would run right over them.

 

If your phone records video, turn it on and point it down the carburetor with your truck running. Flip the accelerator a few times to see if you have a good strong jet of gas going into each barrel..

My money is on your starvation deriving from the squirters

 

I confirmed today that it had a strong squirt. I will try to get a video tomorrow.

 

Hmmmmmm...

Glad you singled out that possibility..

Sorry to be on the Google mechanic side of this now but check this out