rich carb

RJ Sledge · 09-08-2019, 08:51 AM

In my experience on a carb combo it showed rich when staging with 2 step at 3000 rpms or so. Moving O2 or extending collector will correct that.

On an efi combo putting an extension on allowed us to tune it so it did not search and go lean/rich while in 2 step staging. Like the computer couldn’t make up its mind up from due to O2 not getting clean data. That was with a BS3 system but believe it to be the same with all.

Believe Vic’s combo is 780 Holley but maybe not.

RJ

Adger Smith · 09-08-2019, 06:51 PM

2 step = rich reading

Hacksaw · 09-09-2019, 08:06 AM

If it was me I would take out the power valve, plug it and go up 4 jet sizes in the primary. Then evaluate.

Ed Wright · 09-11-2019, 07:36 PM

Cams like we run often causes low enough manifold vacuum to open the power valve at idle. The number on the power valve tells you at what point in manifold vacuum dropping as load goes up, it opens. If it says 85, the power valve opens, and adds fuel at 8.5” of manifold vacuum. A “45” will stay closed, and leaner, above 4.5” of manifold vacuum.

When I had my old IHRA Super Mod Camaro, it had the standard 750 cfm Holley we had to run in NHRA. Was a tad faster than an 850 on that 292”. Before I figured out the “High Speed Air Bleeds”, it was going lean at high RPM. I put a vacuum gauge on it to see if it was pulling vacuum “up there”, it was pulling 3” of vacuum in the lights. I went to a “25” Power Valve, and picked up a MPH. Bigger high speed air bleeds was a tad quicker.

09-08-2019, 08:51 AM	#1
RJ Sledge Senior Member Join Date: Jun 2007 Posts: 783 Likes: 503 Liked 288 Times in 90 Posts	Re: rich carb In my experience on a carb combo it showed rich when staging with 2 step at 3000 rpms or so. Moving O2 or extending collector will correct that. On an efi combo putting an extension on allowed us to tune it so it did not search and go lean/rich while in 2 step staging. Like the computer couldn’t make up its mind up from due to O2 not getting clean data. That was with a BS3 system but believe it to be the same with all. Believe Vic’s combo is 780 Holley but maybe not. RJ

09-08-2019, 06:51 PM	#2
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: rich carb 2 step = rich reading __________________ Adger Smith (Former SS) Last edited by Adger Smith; 09-10-2019 at 11:46 AM.

09-09-2019, 08:06 AM	#3
Hacksaw Senior Member Join Date: Sep 2016 Posts: 884 Likes: 207 Liked 310 Times in 174 Posts	Re: rich carb If it was me I would take out the power valve, plug it and go up 4 jet sizes in the primary. Then evaluate.

09-11-2019, 07:36 PM	#4
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: rich carb Cams like we run often causes low enough manifold vacuum to open the power valve at idle. The number on the power valve tells you at what point in manifold vacuum dropping as load goes up, it opens. If it says 85, the power valve opens, and adds fuel at 8.5” of manifold vacuum. A “45” will stay closed, and leaner, above 4.5” of manifold vacuum. When I had my old IHRA Super Mod Camaro, it had the standard 750 cfm Holley we had to run in NHRA. Was a tad faster than an 850 on that 292”. Before I figured out the “High Speed Air Bleeds”, it was going lean at high RPM. I put a vacuum gauge on it to see if it was pulling vacuum “up there”, it was pulling 3” of vacuum in the lights. I went to a “25” Power Valve, and picked up a MPH. Bigger high speed air bleeds was a tad quicker. __________________ Ed Wright 4156 SS/JA Last edited by Ed Wright; 09-11-2019 at 07:39 PM.