High altitude carburation

[dartboy71]

Here's one for all you guys up high.

I am in Prescott, AZ and the altitude here is about 5200 feet. My father put a 625 carter on my 318 for me this summer at home, which is almost sea-level. I got the Carter rod/jet kit to help me at altitude, but most of my carb-tune reading has been on Holleys.

Last weekend I changed to a rod size that seemed to work. It doesnt bog at either off-idle or hard accel, and I dont even get the surge feel that accompanies poorly tuned secondaries. I have my initial set at 7 BTDC and the mechanical is all in by about 26 BTDC. The jets are stock and the new rod size is the -98 (which I think was .074 x .555). In park, I squeezed the vacuum at idle (with my low compression) up to 16 inches Hg.

The problem: Warmed up, in park, I idle right around 800 rpm, but in gear, it idles around 450-500. I want the drive idle to be around 600-650 without the park idle being up at 1200 rpm, but in all my playing around, I have really messed up the idle enrichment screws and the idle speed screw. Where is the best place to start to correct this?

Since I now have a vacuum gage, can I just turn the enrichment screws all the way in and turn them out until the vacuum maxes out and then adjust the idle, or is there a better way?

[PRO]

dartboy 71,I live in colo at 4600 ft,so I know what your up against.1st youll need a little more initial timing,around 10-12* with a total of 38* max.this alone will help your idle quality,just be sure you dont get any detonation if u do back off the timing 2* at a time untill it quits.Its hard to give you a jet/rod combo because I dont know what your engine combo(compression,cam,int,exh,etc) is,if your not too rich I'll eat my hat though,email me w/your combo & I'll give u a baseline setting....PRO

[ZIPPY]

A good idea with automatic cars is to have somebody else sit in the car and hold the brake with it in gear, while you adjust the idle mixture with the vacuum gauge. You can dial it in a little more accurately that way.