rich carb

RJ Sledge · 09-07-2019, 07:22 PM

If your O2 is in your collector, and it is within 12” from the end, you will not get a “clear” read, it will always show rich until you bring up rpms as in making a pass down the track then it will read correctly.
You can slip on an 18” extension to the end of collector and tune it for lower rpms (2 step leave or foot brake leave). Then take off extension. It’s is sucking air back up past the O2 sensor and it will show rich until you get rpms up and going down track.

Good luck
RJ

Darrel Goheen · 09-07-2019, 09:14 PM

Quote:

Originally Posted by RJ Sledge

If your O2 is in your collector, and it is within 12” from the end, you will not get a “clear” read, it will always show rich until you bring up rpms as in making a pass down the track then it will read correctly.
You can slip on an 18” extension to the end of collector and tune it for lower rpms (2 step leave or foot brake leave). Then take off extension. It’s is sucking air back up past the O2 sensor and it will show rich until you get rpms up and going down track.

Good luck
RJ

Actually it'll show lean.

Glenn Briglio · 09-08-2019, 08:37 AM

Put O2 sensor in primary pipe.

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.

09-07-2019, 07:22 PM	#1
RJ Sledge Senior Member Join Date: Jun 2007 Posts: 783 Likes: 502 Liked 288 Times in 90 Posts	Re: rich carb If your O2 is in your collector, and it is within 12” from the end, you will not get a “clear” read, it will always show rich until you bring up rpms as in making a pass down the track then it will read correctly. You can slip on an 18” extension to the end of collector and tune it for lower rpms (2 step leave or foot brake leave). Then take off extension. It’s is sucking air back up past the O2 sensor and it will show rich until you get rpms up and going down track. Good luck RJ

09-08-2019, 08:37 AM	#3
Glenn Briglio VIP Member Join Date: Nov 2002 Location: Massapequa Park,NY Posts: 1,282 Likes: 1,896 Liked 970 Times in 308 Posts	Re: rich carb Put O2 sensor in primary pipe. __________________ 1989 Camaro Iroc-Z I/SA B&B Auto Machine Shop.

09-08-2019, 08:51 AM	#4
RJ Sledge Senior Member Join Date: Jun 2007 Posts: 783 Likes: 502 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	#5
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	#6
Hacksaw Senior Member Join Date: Sep 2016 Posts: 882 Likes: 206 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	#7
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.