"Misses" at Idle, but not at cruise RPM???
 

I have a 72 GMC K2500 with a 25000 mile or so Mr. Goodwrench crate engine. I just replaced the tired old original carb,as well as the original intake manifold with Edlebrock "performance." parts. Also put in a new EFI distrbutor and new plugs and wires. Truck runs great now! Only problem is that at idle (800 RPM) the engine seems to have a big miss that you can feel in your seat! As soon as speed increases, the engine smooths out nicely. Since I already replaced the ignition parts, I'm now guessing valves or maybe a vacuum leak. Anybody wanna take a shot at this?
Thanks in advance for the help.

Re: "Misses" at Idle, but not at cruise RPM???
 

Likely runs smoother due to increased timing.

At your elevation you need to do two things.
Lean your carb jets down.
Recurve your timing.
You need lots of initial timing.
Likely in the 16-18 degree area. Then you need to limit the mechanical timing in the hei to 14-18 degrees.
Vac advance might need tweaking too. Limit it to 12 degrees.

Having said all that here’s a question.

What’s your initial timing at?
Can you adjust either mix screw on the carb almost shut and not kill the motor?

Re: "Misses" at Idle, but not at cruise RPM???
 

My money is on a vacuum leak around the base of the carb

Re: "Misses" at Idle, but not at cruise RPM???
 

Check for a vacuum leak at the vacuum outlet in the manifold. It can lean out 1 or 2 cyls. & cause a rough idle & miss at idle especially with an auto trans in drive. Check the power brake unit, trans modulator & heater/ac vacuum hoses & reservoir.

George

Re: "Misses" at Idle, but not at cruise RPM???
 

If you installed a Performance manifold and a 14xx family carb, did you get the needed adapter plate? If not, probably your vacuum leak.

A lot of Eddy carbs are rich out of the box, you may need to adjust for your altitude. Also the float levels are often off out of the box.