Pete-87-22r

Hi, I've been reading here for a while and it's been really helpfull so far but I've got a few questions I cant find answers to.
First being about my carb, my truck's from Ft. Collins CO. and I live in Southern California, I'm having trouble getting the carb tuned right, when I set the warm idle to the 700rpm or so that most websites reccomend i get a pretty rough idle, but up at 775-800 its smooth and feels right, other than I know its wrong. I'm thinking that the altitude might need a different setting on the idle mixture or something. If anybody knows about this that would be a huge help. I really don't want to have to rebuild this thing.
Thanks, Pete
Truck has a manual transmission, 4x4, everything stock

slow-mo

I'm assuming your Colorado vehicle has the whole High Altitude Compensator (HAC) vacuum system?

http://www.utoyot8.com/FullImage.asp...708%2922R..USA


If so, then maybe you have some issue with the system. Only way to confirm that it is operating correctly is to check it with the factory service manual (FSM). Mine is already a California truck so I have no experience with such a contraption.


Also, check your timing to confirm that it is correct. That procedure is also in the FSM.

Pete-87-22r

Okay, found out I do have the HAC system. I'm completely new to carbs (this is my first truck) and the 85 FSM I got (supposed to have the most carb info) says nothing about the HAC system. Is this something I can remove and move on or does it even do anything at low elevations? I see it has a vaccuum line coming from the distributer vac line. I cant seem to find much on this so any help is greatly appreciated.
Thanks

slow-mo

Do you have the FSM on PDF that can be downloaded from the internet?

My 1987 FSM in print has the info on the HAC, but I did not pay much attention to it since I don't have it.

I can only assume that it could be removed. You will probably have to plug some of the vacuum ports and maybe run new vacuum hoses but that is only a guess.

From what I did read, the HAC is a self-regulating device that senses the high altitude, low atmospheric pressure and compensates the air intake and idle advance.

I have not read anywhere that the HAC vehicles also are rejetted differently than the other Federal (49-state) vehicles. I do know that the California (50-state) carburetors have a larger main jet than the Federal carburetors.