idle mixture screws

Posted By: PJ68RT

idle mixture screws - 06/25/10 01:48 PM

Should the engine die when i close both idle mixture screws on an e-brock carb? I closed both of them down and it dropped the idle speed from 800 to about 600rpm. Would this be a symptom of a vac leak somewhere in the carb or gasket??

Posted By: 540challenger

Re: idle mixture screws - 06/25/10 01:56 PM

If you turn the both screws all the way in yes it will kill the engine. You are basiclly cutting off all the full at idle.

No this is not a system of a vac. leak.

What is the problem you are having or are you trying to set the carb up????

Posted By: PJ68RT

Re: idle mixture screws - 06/25/10 02:28 PM

What i'm saying is that i did close them all the way and the engine didn't die...it just reduced the idle speed from 800 to 600rpm. Since it didn't die would that be a symptom of a leak?

Posted By: Mr.Yuck

Re: idle mixture screws - 06/25/10 02:33 PM

Quote:

What i'm saying is that i did close them all the way and the engine didn't die...it just reduced the idle speed from 800 to 600rpm. Since it didn't die would that be a symptom of a leak?

turn them out a full turn. Hold your hand over the carb cocking off all the air. If it doesn't shut off then you have a vacuum leak. However what the guy was saying is even with a vaccum leak, if you turn all the gas off the engine should die. I'm wondering if your floats are set to high. I know on a holley if they are gas pours out the vent tubes and into the carb.

Posted By: 540challenger

Re: idle mixture screws - 06/25/10 02:38 PM

Quote:

What i'm saying is that i did close them all the way and the engine didn't die...it just reduced the idle speed from 800 to 600rpm. Since it didn't die would that be a symptom of a leak?

IMO if you had a vac leak that would lean out the carb further. and it should shut off. However every combo is different and depending if the needle on the mixture screws could still let some fuel thru if not seated correctly. Also how far are the throttle blades open if open too far you could be not on the idle circut off the carb??

Posted By: PJ68RT

Re: idle mixture screws - 06/25/10 02:48 PM

I'm sure the blades are not open much at all and it should be in the idle circuit..but i will double check that. Initial timing is 15deg.

This is the P.O.S 750 eddy carb that im dealing with. I do have the orig AVS that i'll probably swap on and see how it does.

I just pulled the car out of storage for the last two years and am just making sure everything is ok. Thanks for the replies.

Posted By: 540challenger

Re: idle mixture screws - 06/25/10 02:57 PM

Quote:

This is the P.O.S 750 eddy carb that im dealing

Setting for 2 years it couldn't hurt to take the top off the carb and go through it. Every eddy carb i have taken apart the float level and drop was way off. Double check that clean out the passages maybe it has a needle hanging open a little

Posted By: mopowergtx

Re: idle mixture screws - 06/25/10 03:34 PM

But yes if you screw even one of the idle mixtures screws in all the way the engine should die if everything else is right. IE no vacuum leaks and the throttle blades arent open past the idle circuit slots. You got a factory service manual? It explains how to set the idle screw on a fresh rebuilt carb and the procedures would be the same for the Eddy as the stock Carter. That way you know your not to far open to be getting were your running on the main circuit versus the idle circuit. Now depending on the year the idle mixture screw system could be alot different. Like for instance a 69 AVS idle mixture setup is not going to be apples to apples but a FSM for lets says a 1967 AFB on a 440 would be.

Posted By: MoparforLife

Re: idle mixture screws - 06/25/10 04:05 PM

Just a note here. When you screw those needles in just barely let them touch the seat. don't screw them in tight or you can possibly groove the brass needle rendering the needle virtually useless.

Posted By: PJ68RT

Re: idle mixture screws - 06/25/10 04:07 PM

Thanks for the info

I do have a service manual. I'll dig it out and read up.