Carb setting help
Thread Starter
2nd Gear
Joined: Aug 2023
Posts: 2
Likes: 0
Carb setting help
Just had my 454 rebuilt and the mechanic put a used Holley 650 double on it but didn’t set it up properly… he re-jetted it saying it’s running to lean and now I see nothing but black smoke when idling. I put a vacuum gauge on it and my highest vacuum is when I close the front two mix screws completely closed…
can I assume that the jets he installed are just to large or do I have something else going on…
please help
can I assume that the jets he installed are just to large or do I have something else going on…
please help
Drifting
Joined: Feb 2015
Posts: 1,440
Likes: 1,031
From: Baton Rouge Louisiana
Your idle isn't affected by your jetting. It's determined by your transfer slot and idle mixture screws - which you should have 4 corner idle on a DP. Is this a new carb? Have you read Lars' paper on Holley set up?
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Jetting has no effect on idle rich/lean condition. In fact, you can take the jets completely out of the carb and the idle will remain unchanged, as long as the carb is idling on the idle circuit. You have something else going on - carb needs a complete baseline setup... Sounds like your hack "mechanic" is a real gem.
Lars
Thread Starter
2nd Gear
Joined: Aug 2023
Posts: 2
Likes: 0
no it’s a used carb.
no I have not read Lars.
I was on holleys web site and watched a bunch of set up videos… it said if you have black smoke to down size 2 jet sizes… it didn’t talk about why when I bottom out the mix set screws I get the highest vacuum… normally the highest vacuum should be somewhere around 1-1/2 turns out not turned all the way in.
Last edited by keno3434; Aug 28, 2023 at 11:57 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Few Holleys will run at 1-1/2 turns. Most are at 5/8 to 7/8.
If the engine is running with the mixture screws all the way in, the carb is supplying fuel to the engine through some source other than the idle circuit. Most likely from fuel dribbling out of the main discharge nozzles. You need to tear that carb down and do a correct setup on it.
If the engine is running with the mixture screws all the way in, the carb is supplying fuel to the engine through some source other than the idle circuit. Most likely from fuel dribbling out of the main discharge nozzles. You need to tear that carb down and do a correct setup on it.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Few Holleys will run at 1-1/2 turns. Most are at 5/8 to 7/8.
If the engine is running with the mixture screws all the way in, the carb is supplying fuel to the engine through some source other than the idle circuit. Most likely from fuel dribbling out of the main discharge nozzles. You need to tear that carb down and do a correct setup on it.
If the engine is running with the mixture screws all the way in, the carb is supplying fuel to the engine through some source other than the idle circuit. Most likely from fuel dribbling out of the main discharge nozzles. You need to tear that carb down and do a correct setup on it.
It is easy to see while running....shine a pen light down the primary venturi and see if it is dribbling gas out of the boosters.....if it is, you are taking it apart.
Jebby
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