Rough Idle

[texasmike]

I replaced my carb about two years ago with a Rochester Qjet from National Carburetors in Jacksonville Fla. All of their carbs are supposed to get a live engine test with adjustments set for a bolt on and go carburetor. I bolted it on and went around 3,800 miles ago and it has operated well except for a rough idle when the AC is on and I am stopped with the auto transmission in gear. I decided to see if I could smooth the idle out so I watched a youtube video about the adjustment process. I connected a vacuum gauge to the PVC port on the carb and it read 18 in Hg. When I tried to use my straight slot screwdriver to turn the air-fuel mixture screws, it would not work. it's real hard to see what kind of tool it would take to turn the screws. It almost looks like a hex head for a very small socket wrench. Can anyone tell me what I need and the best place to find it? Thanks for the reply.

 

[Bextreme04]

I replaced my carb about two years ago with a Rochester Qjet from National Carburetors in Jacksonville Fla. All of their carbs are supposed to get a live engine test with adjustments set for a bolt on and go carburetor. I bolted it on and went around 3,800 miles ago and it has operated well except for a rough idle when the AC is on and I am stopped with the auto transmission in gear. I decided to see if I could smooth the idle out so I watched a youtube video about the adjustment process. I connected a vacuum gauge to the PVC port on the carb and it read 18 in Hg. When I tried to use my straight slot screwdriver to turn the air-fuel mixture screws, it would not work. it's real hard to see what kind of tool it would take to turn the screws. It almost looks like a hex head for a very small socket wrench. Can anyone tell me what I need and the best place to find it? Thanks for the reply.

You can get these from the big box parts stores too, but this is the one I bought to adjust mine. The stock mixture screws will be the "double D" or a double d with a slot cut in them. Most aftermarket ones go to a small hex head. I had the double D and then converted to the hex head and both were able to adjust with this tool. It also makes it much easier to adjust due to the flex shaft... it can get pretty awkward trying to get a screwdriver on there with the engine running and the long flexible shaft makes it a breeze.

https://www.amazon.com/dp/B000CMDP80/

 

[Backfoot100]

Do you have the A/C solenoid hooked up and adjusted on the throttle linkage? That solenoid gets adjusted to increase idle a couple hundred RPM when the A/C is turned on.

 

[Jimbarry]

I just slipped a piece of hose over the jet head to turn it with and marked the adjustment when I got the best vac reading. I left the hose on.

 

[texasmike]

Thanks everyone, all good points and ideas, very helpful.

 

[Bextreme04]

I just slipped a piece of hose over the jet head to turn it with and marked the adjustment when I got the best vac reading. I left the hose on.

Do you not have the springs on the back of the screws? Mine are way too tight to turn using a hose like that.

 

[Jimbarry]

Do you not have the springs on the back of the screws? Mine are way too tight to turn using a hose like that.

Mine have springs but they turn just fine, it has to be a tight fit, I put them in hot water to get them on. You can also put a little epoxy/glue in the hose and let it set, just be sure you don't glue the threads. I can bottom them out (by feel) and run them all the way out. Never had a problem. Like I said, I just leave the hoses on both sides for easy adjustment.

 

[Matt69olds]

You can also remove the screws a carefully cut a slot in them to allow adjustment with a screwdriver, just the way God intended carb adjustments to be made!!

Remove each screw, make sure you don’t drop the spring behind it. Use a deemed tool with a cut off wheel to make a tiny slice in the tip of the adjustment screw. Reinstall, and adjust the idle.

I agree with needing to solenoid stepper motor. Wire it in to the compressor power feed wire ahead of the low pressure switch. That way the solenoid is engaged as soon as you turn on the air. I don’t think the solenoids have enough force to actually open the the throttle, it will hold it slightly off its base setting.