looping idle

[nailem]

1986 4bb Rochester merc 5.0L. what do i need to adjust? my idle seems to ok for about 30sec to 1min then it starts to loop is the best way i can put it. it goes up and down from about 500rpm to 800rpm up/down up/down. any suggestions?

 

[nailem]

Re: looping idle

i know there is good rochester guys on here. do i need a rebuild or can this be adjusted

 

[maxxman04]

Re: looping idle

i've been doin a bit of research online and in my own head, trying to recall my days of carbs, but i have to agree. it sounds alot more like a vacuum leak, or possibly a weak fuel pump. check or have checked the fuel pressure and amount of vacuum. both are easy to do. it may not hurt to check compression as well.

 

[a70eliminator]

Re: looping idle

have you tried adjusting the mixture screws front of the carb base. Sounds like it's idling too fat, andf if I'm right the plugs are now fouled and need to be removed and cleaned or replaced before you go and further.

 

[brian_mcwhirter]

Re: looping idle

Sounds like you've got the old quadrajet, and I just went through this whole thing myself. With the engine idling, take a look down the carb throat. You shouldn't see any gas dribbling out of the jet. If you do (like I did), you've got a carb issue. I took mine apart and noticed a couple of things. For one, the needle valve had come completely out of it's seat, causing an extreme rich and flooding condition, and secondly, the screws holding the base to the throttle body were loose. I soaked everything in carb cleaner overnight, blew it out real well, and reassembled it. Idles much better now. As long as your gaskets are OK, and your needle doesn't show any wear, you shouldn't need a rebuild kit. Good luck!

 

[nailem]

Re: looping idle

thanks, it is a quadrajet and i will have to look again but it might have a little dribble problem. seems like i saw fuel in one side misting more and the other side less spray and more dribble.

it seems like the mixture screws do little for me. when turned all the way in i can stall the motor but anything out from that does not seem to change anything. i have them 1.5 turns out only because that is what i read as a starting point. 1/4 turn seems the same as 1.5 though.

i will try to get a hold of a gauge to check the fuel psi.