A/F too rich
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
A/F too rich
Still sorting out stalling problems with the 540. I switched out the k66 ti for a borrowed HEI and it runs great but the a/f is way off. I'm running 12.2:1 at 3000rpm cruise and 10.5:1 at 6000rpm WOT. I'm using an LM2 wide band. I set
the idle last weekend in hot weather to 13.8:1 and 850rpm. With cool weather today it was running at 12.5 at 920rpm.
The carb is a Quick Fuel ss-850 with 80 primary jets and 88 secondary jets. Would it be too much to go to 72 primary and 80 secondary jets? I have all incremental 70's jet sizes but no 80's except for what is installed. Also, before I got the wideband a tuner/builder could just smell it was rich so we put in a 5.0 power valve. I could go back to the 6.5 pv.
Engine is a CNC 540 short block with flat tops. Heads 1967 L88 closed chamber. Comp Cams solid roller grind CB 4873B//4874B.
Any helpful comments are appreciated.
TT
the idle last weekend in hot weather to 13.8:1 and 850rpm. With cool weather today it was running at 12.5 at 920rpm.
The carb is a Quick Fuel ss-850 with 80 primary jets and 88 secondary jets. Would it be too much to go to 72 primary and 80 secondary jets? I have all incremental 70's jet sizes but no 80's except for what is installed. Also, before I got the wideband a tuner/builder could just smell it was rich so we put in a 5.0 power valve. I could go back to the 6.5 pv.
Engine is a CNC 540 short block with flat tops. Heads 1967 L88 closed chamber. Comp Cams solid roller grind CB 4873B//4874B.
Any helpful comments are appreciated.
TT
Le Mans Master
Joined: Mar 2001
Posts: 5,738
Likes: 644
From: Lincoln, CA
I dropped 10 jet sizes on the primary and went smaller on the idle feed restrictors to get my SS830 dialed in. It's hold close to 14.7 around town.
I didn't need to touch the PV or Secondary sizes. Also get the Sec idle screw as it makes it so much easier to dail in.
I didn't need to touch the PV or Secondary sizes. Also get the Sec idle screw as it makes it so much easier to dail in.
Last edited by ddawson; Jun 6, 2020 at 08:12 PM.
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Lars
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Just follow the article ddawson posted to a tee. You will establish your initial timing using a vacuum gauge and then tune the carb fuel circuit by fuel circuit. It's a great tuning method and worked for me.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
I can try the staple wire in the IFRs for now per Lars. Thanks for the article Dan. For the base timing is the vacuum advance removed? Does it get hooked up later? Do you remember what size IFRs you ended up with? Did you start with blanks and drill them?
Thanks
TT
Thanks
TT
