Carb & Idle Help

[RDrancher]

I've dealt only with diesels for the last 15 years, so I could use some help with this. I recently purchased this low mileage '85 Suburban. The previous owner replaced the HEI cap, plugs, wires and a rebuilt Quadrajet. I believe the carb is a smog model since the idle mixture adjustments are epoxied.

The engine runs nice but has a rough idle and smells pretty rich. After replacing all of the vacuum lines and plugging the ones on the carb that looked to be heading to emission stuff, I bumped the timing up by ear (no timing tab on the engine). It runs better, but didn't change the rough/rich idle.

I could use help in resolving the rough/rich idle, but first...where does the hookup my finger is pointing to in the photo tie in? I think it's for the secondaries, but could it have anything to do with idle and fuel mileage? The smaller hookup under that's same pot is tied into the vacuum system. [IMG][/IMG]

I plan on swapping the carb/manifold out for an Edelbrock setup, but for the time being, if I can get it running right I could use those funds for drop spindles and springs.

Sorry for the huge pic, I'm still figuring this site out. Thanks.

[c3006]

I think that's the secondary pull off and has to do with holding tension on the choke plate and I imagine it could have to do with it running rich if it is not holding the choke open once warmed up. Mine is hooked to one of the vacuum ports on the front of the carb.

[RDrancher]

I hooked it up to the lower passenger front port on the carb. I believe that this is manifold vacuum. It helped some, but didn't stop the problem. Funny thing is that when I started it hooked up this way it was perfect until I touched the throttle.

[geezer#99]

THere's a possibility that nipple on the back of the pot is not the one you hook up to manifold vacuum. The nipple is on the side pointing towards the valve cover and hooks to a small vac port on the back of the carb.

[RDrancher]

Originally Posted by geezer#99

THere's a possibility that nipple on the back of the pot is not the one you hook up to manifold vacuum. The nipple is on the side pointing towards the valve cover and hooks to a small vac port on the back of the carb.

Yes, the smaller vac port is connected to manifold vacuum at the back of the carb.

I also tried hooking the nipple in the pic to the carb port at the upper front passenger side port. I think that this is the one that would go to the stock air cleaner. It didn't seem to help at all, but if I leave this port open on the carb the idle goes up and does help it idle a bit cleaner. I'm sure I can't leave the port open though.

I think that this carb is one of the Edelbrock rebuilds. I had one on a 350 in a Land Cruiser. That carb was horrible and acted a lot like this one. I put another non-smog carb on that ran better straight out of the junkyard.

[Dead Parrot]

Is the choke fully open when hot? If not, you need to loosen the 3 screws holding the black cover on the thing in the lower right of your picture and turn until the choke is fully open. There might be a rich-lean mark on the side of it. A mis-adjusted choke can cause your too rich problem.

[frank69]

That's a computer controlled carb. I doubt if it will ever run right with stuff like the egr lugged off. Best thing to do is get rid of it unless u have smog laws. That has been my experience anyway.

[INSIDIOUS '86]

Usually in older q-jets they have pressed in plugs on the bottom that start leaking after so many heat cycles. Usually this causes a rather rich idle and is hard to find the cause of the rich idle very hard. The mixture plugs can be pulled off.

You can pull the carb off and steel wool the main well plugs and spray some carb cleaner on them then epoxy them up and it should help solve the issue

Another thing to look at is timing. You want the vacuum advance to MANIFOLD vacuum and set at 12* btdc