And also could you tell me everything that needs to be adjusted after, the choke is adjusted and how to do that. The carb is a 86 ccc q-jet.Thanks

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Wish i could help, but choke tuning is one thing i do purely based on magic and experience. Basically, i set how tight the choke closes based on feel and my perception of ambient temperature (in hot weather it shouldn't really be tightly closed, but still snaps shut.) And then i tune it from there if i find it taking too long/short to come off.

I set the pull off based on how it runs once it fires w/o touch the gas pedal. If it basically stalls it is opening too much, if it misses/stalls, it isn't opening enough.

And don't forget the fast idle speed needs to be set before you really get into this stuff.

Honestly, even if you had a factory service manual and all the funny angle guages and set everything to spec, i don't think you can beat practice and leanring how to set it by feel. All my carbed cars started on the first turn of the key every time with no pumping (beyond getting it on the fast idle cam), except in the coldest of weather, and even then they immediately light off the second time you touch the key.
a lot of help, huh...ed

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Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

 

Yeah, you set it on experience and "feel."

I ALWAYS get the HOT idle set right before tackling the choke- and that includes checking the ignition timing.

When overnight-cold, open the throttle 1/2 way by hand with the air cleaner off. Choke plate should SNAP fully closed. If not you might have binding linkages or a bad choke element. But let's assume that's all OK.

Immediately after starting the vacuum diaphragm on the pass. side of the carb will pop the choke plate open about 3/16" and keeping it from flooding the engine. Most "choke" problems where the engine dies soon after startup are related to this being out of adjustment. The adjustment for this is on the arm of the vacuum diaphragm. It's a phillips-head screw that points straight back. Turning it clockwise will reduce choke opening (richer), CCW, it will increase the opening (leaner). Often it is a good idea to simply force the choke plate further open and closed by hand immediately after starting on a cold motor just to see if it really wants to go leaner (more opening) or richer (less opening) before making any adjustment to the screw. So you know which way to go. You only get about 30 seconds on each cold startup to play with it before there is too much heat in the intake and the choke starts to pull off by itself. Make final tuning adjustments over a series of days until you get it to run smooth right from startup.

The fast idle speed screw is also located on the same side as the choke. It's a regular-slot screw UNDER all the choke linkage that you can see looking under the carb from the front of the engine. This screw ONLY adjusts idle speed when the choke is ON. Once the choke fully releases, it does nothing. It's a sensitive adjustment. Go in 1/4 turn steps to rough it in, 1/16 after that. Idle speed on an overnight-cold engine should be about 1200-1400 (neutral). At half choke it should drop down to about 900 and then to normal idle speed once fully released.

 

btt

 

btt

 

Dude, that's basically all there is to know. There is a ****load of info packed into the above posts. Like every word is critical.

THe only thing else I can add is this. Make adjustments in the following order:

1. Choke pulloff adjustment screw. Adjust so that just after the overnight-cold engine fires up that is idles smoothly. If in doubt, go too lean (too much choke opening) rather than too rich. A good way to tell if you're too rich or lean is to take off the air cleaner lid and fire the OVERNIGHT COLD motor. IMMEDIATELY go to the choke plate and move it by hand futther open and then further closed. See where it WANTS to be to idle a cold engine smoothly. Make sure that the choke pulloff adjustment screw is adjusted to open the choke plate exactly that much as soon as the engine fires up. like Ed said, it's a "feel" kinda thing. No mathematical formula or measuring device can figure this out for you, but like I said, 3/16" choke opening after initial startup will get you in the ballpark for starters.

2. THEN set the fast idle speed. The fast idle speed adjustment screw is located underneath the choke linkage and is only visible when viewed from the FRONT of the carb with the choke FULLY ON. It's usually a hex-head screw with either a slot for a regular/phillips screwdriver or a torx head screwdriver. This screw ONLY affects the idle speed when the choke is ON or partially on. Once the choke fully releases this screw makes NO difference in idle speed. Adjust so that you get an idle speed of about 1200-1400 RPM immediately after cold startup in the morning. The adjustment is sensitive- 1/4 turn makes a pretty big difference in idle speed.

3. Go through a few more rounds of steps 1 and 2 again. This willhelp you zero in on optinum settings. In a few weeks of cold starts you will have that puppy DIALED IN on cold starts real well!

That's about it. Any more adjustements would involve bending of various choke linkages and that's not what you want to tackle right off the bat.