Engine running lean on one side.

COPPERN · 05-01-2011, 01:38 AM

Sbf running lean on the drivers side .A/f ratio was 15:1 and pass side at
approx 13:1 went up 6 jets front and rear and it is still lean.Engine is a 349 with a single plain intake and 950 hp carb.Thinking problem may be
with the carb or a vacuum leak.
Any help would be appreciated.

Phillip marvetz · 05-01-2011, 02:36 AM

Sounds like intake is not sealing. Have you pulled it to have a look at the gasket surface?

Rick Leininger Jr. · 05-01-2011, 06:22 AM

Yes, sounds like a leak. Pull some spark plugs and look at them to verify running lean.

Adger Smith · 05-01-2011, 07:19 AM

Switch the leads and the sensors. Verify it isn't the way you are reading it. Like Rich said.... Pull the plugs and verify it is lean. If you went up that many jets the reading should have changed. I would say something in the data system is subject if the plugs look ok. If it is reading correctly and still showing lean then there might be a fuel supply problem. Increasing 6 jets if a fair amount of change.

BlueOval Ralph · 05-01-2011, 08:45 AM

a leak in the headers or collector?

Quote:

Originally Posted by Adger Smith

Switch the leads and the sensors. Verify it isn't the way y
ou are reading it. Like Rich said.... Pull the plugs and verify it is lean. If you went up that many jets the reading should have changed. I would say something in the data system is subject if the plugs look ok. If it is reading correctly and still showing lean then there might be a fuel supply problem. Increasing 6 jets if a fair amount of change.

COPPERN · 05-01-2011, 10:32 AM

The plugs are reading very lean, sensors and leads were swapped side to side and changed to verify the were working properly and fuel pressure was at 7.5 pounds using 2 differernt gauges. I will look for a possible vacuum leaks next. Thank you to everyone who replied .

Adger Smith · 05-01-2011, 12:14 PM

If this is a new combination w/new or un used carb you may have Hi speed A/B's that are too big. Check all sizes of the A/B's (Hi & low) before going any further, just to be sure. They may have done an unintentional swap when doing assy of the carb. I lost the main bearings of a nice 565 on the dyno because it was very lean in the middle (17-1 AF) of the pull. It took 2 1/2 pulls to detonate enough to hurt the bearings. It ran through the lean area and was 13. 2 A/F up high. It was because the carb builder left the A/B's for the intermediate circuit out of the carb. We thought the new carb was OK and didn't even look at it when installing it on the Dyno. I now check everything on the carb before starting with a new unknown/tested combo.

05-01-2011, 01:38 AM	#1
COPPERN Junior Member Join Date: Apr 2009 Posts: 13 Likes: 0 Liked 0 Times in 0 Posts	Engine running lean on one side. Sbf running lean on the drivers side .A/f ratio was 15:1 and pass side at approx 13:1 went up 6 jets front and rear and it is still lean.Engine is a 349 with a single plain intake and 950 hp carb.Thinking problem may be with the carb or a vacuum leak. Any help would be appreciated.

05-01-2011, 02:36 AM	#2
Phillip marvetz Senior Member Join Date: Oct 2008 Location: Lynden ,WA Posts: 820 Likes: 0 Liked 3 Times in 3 Posts	Re: Engine running lean on one side. Sounds like intake is not sealing. Have you pulled it to have a look at the gasket surface? __________________ 2009 V/SA Record Holder

05-01-2011, 06:22 AM	#3
Rick Leininger Jr. Member Join Date: Jun 2007 Posts: 162 Likes: 0 Liked 0 Times in 0 Posts	Re: Engine running lean on one side. Yes, sounds like a leak. Pull some spark plugs and look at them to verify running lean.

05-01-2011, 07:19 AM	#4
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: Engine running lean on one side. Switch the leads and the sensors. Verify it isn't the way you are reading it. Like Rich said.... Pull the plugs and verify it is lean. If you went up that many jets the reading should have changed. I would say something in the data system is subject if the plugs look ok. If it is reading correctly and still showing lean then there might be a fuel supply problem. Increasing 6 jets if a fair amount of change. __________________ Adger Smith (Former SS) Last edited by Adger Smith; 05-01-2011 at 07:20 AM. Reason: sp

05-01-2011, 10:32 AM	#6
COPPERN Junior Member Join Date: Apr 2009 Posts: 13 Likes: 0 Liked 0 Times in 0 Posts	Re: Engine running lean on one side. The plugs are reading very lean, sensors and leads were swapped side to side and changed to verify the were working properly and fuel pressure was at 7.5 pounds using 2 differernt gauges. I will look for a possible vacuum leaks next. Thank you to everyone who replied .

05-01-2011, 12:14 PM	#7
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: Engine running lean on one side. If this is a new combination w/new or un used carb you may have Hi speed A/B's that are too big. Check all sizes of the A/B's (Hi & low) before going any further, just to be sure. They may have done an unintentional swap when doing assy of the carb. I lost the main bearings of a nice 565 on the dyno because it was very lean in the middle (17-1 AF) of the pull. It took 2 1/2 pulls to detonate enough to hurt the bearings. It ran through the lean area and was 13. 2 A/F up high. It was because the carb builder left the A/B's for the intermediate circuit out of the carb. We thought the new carb was OK and didn't even look at it when installing it on the Dyno. I now check everything on the carb before starting with a new unknown/tested combo. __________________ Adger Smith (Former SS) Last edited by Adger Smith; 05-01-2011 at 12:16 PM. Reason: sp