Carb running too rich
Thread Starter
Burning Brakes
Joined: Oct 2001
Posts: 1,241
Likes: 4
From: Okinawa Okinawa
Carb running too rich
I rebuilt my carb and readjusted everything. The floats are set, idle, and is set for maximum vacum. I am still running really rich. The plugs are almost caked on black and a pretty foul smell out of the exhaust. I know I will loose some vacum but how do you tell when it is set right and not too lean? I think after you have an RPM drop you turn in rich about 1/4 turn.
Drifting
Joined: Mar 2001
Posts: 1,896
Likes: 0
Re: Carb running too rich (scottw)
I think the best way would be to take a vacuum gauge and hook it up to a manifold port. Raise the RPM to 1000-1500 and set the idle screws until the HIGHEST possible vacuum is reached. That's what I do an it seemd to work pretty well.
:chevy
Aaron
:chevy
Aaron
Thread Starter
Burning Brakes
Joined: Oct 2001
Posts: 1,241
Likes: 4
From: Okinawa Okinawa
Re: Carb running too rich (Aaron-74)
I set it at 1500 RPM and the max vacum was with the idle screws all the way in. It was at 20 inches. I unscrewed them one turn and it went down to 19 inches. Do I need to possibly change the jets to a smaller size? I have no idea what size is on right now
Advanced
Joined: Aug 2002
Posts: 84
Likes: 0
From: Riockwall Texas
Re: Carb running too rich (scottw)
Sounds like your power piston is hanging up in the full "up" position. If the carb ran OK before you rebuilt it, the jets don't cause a change in running, since they were not changed. You could have an incorrect baseplate gasket which could mask off a vacuum port for the power piston.
Don't try to set the idle mixture at 1500 RPM. You are not on the idle circuit at that RPM. Set idle at recommended idle speed, around 750-800 RPM. If you can't get the idle speed down that low, you must find the problem causing the high idle first.
Good Luck.
Don't try to set the idle mixture at 1500 RPM. You are not on the idle circuit at that RPM. Set idle at recommended idle speed, around 750-800 RPM. If you can't get the idle speed down that low, you must find the problem causing the high idle first.
Good Luck.
Instructor
Joined: Nov 2001
Posts: 175
Likes: 0
From: St Louis MO
Re: Carb running too rich (scottw)
An excellent rebuild book for the holley 1850 carb is published by S-A Design, Holley rebuilding and modifying. If your idle screws are not making much difference in the quality of idle then you may have the primaries open too far and uncovering the ports that take it off the idle circuit. The preliminary adjustment for the idle speed on the primaries is to turn in the screw until the butterflies just begin to move, then one additional turn. Also don't forget to set the secondary butterflies. Again you adjust them to the point where the the secondaries just start to move, then an additional 1/4 turn. A hotter cam may require you to open the secondaries even a little more so that you are not opening the primaries too far and taking the carb off the idle circuit. Hope this helps. :chevy
