wideband o2 Carb adjustment
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Cargo Master
Joined: Oct 2004
Posts: 2,148
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From: Seneca, SC
wideband o2 Carb adjustment
ok so as a setup I've got a 300I6 with a moderate build on it including a truck avenger 470 from Holley, and I've gotten tired of the absurdly bad mileage so I put an AEM o2 kit in the x-pipe, and have been tuning for good mileage/power.
Everything that I've read on the subject says that I've got to have about 12.5 or thereabouts for peak power,and 14.7 or so for peak mileage. With three jets down on the primaries and a lot of time messing with the idle speed/idle mixtureI think that I've got this thing set about as close as I can get it, but I've got a slight problem. Under really light throttle coming off idle while cruising, I can get the engine to go stupid lean. I don't get any backfire, and under a mild/moderate throttle off idle there's no issue. I guess I've gotta drive the truck some more to see if there's a lag or bog, but I'm wondering what you guy's thoughts are on the subject.
Also a big shout out to Harte3 for telling me to run a different carb spacer and flip my carb around. I didn't until now and got a lot more mid range power out of the setup.
Everything that I've read on the subject says that I've got to have about 12.5 or thereabouts for peak power,and 14.7 or so for peak mileage. With three jets down on the primaries and a lot of time messing with the idle speed/idle mixtureI think that I've got this thing set about as close as I can get it, but I've got a slight problem. Under really light throttle coming off idle while cruising, I can get the engine to go stupid lean. I don't get any backfire, and under a mild/moderate throttle off idle there's no issue. I guess I've gotta drive the truck some more to see if there's a lag or bog, but I'm wondering what you guy's thoughts are on the subject.
Also a big shout out to Harte3 for telling me to run a different carb spacer and flip my carb around. I didn't until now and got a lot more mid range power out of the setup.
Laughing Gas
Joined: Dec 2003
Posts: 900
Likes: 3
I'd try richening the idle mixture a bit to see if the lean tip in goes away. I tried to set my straight six Chevy and the 302 in my truck to a 14.7 idle and both of them hated it. They both run much smoother and happier at 13.8. Every engine is different so who knows. On the six, you have to be careful. Your sensor is showing an average of 14.7 for the whole motor, but keep in mind with that type of intake, the center cylinders will run a bit rich since they're closer to the carb, and the end cylinders will be leaner due to the distance from the carb. So, your end cylinders are probably way leaner than 14.7.
If that doesn't work maybe switch to a power valve that comes in a little sooner.
If that doesn't work maybe switch to a power valve that comes in a little sooner.
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Cargo Master
Joined: Oct 2004
Posts: 2,148
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From: Seneca, SC
good call Jade. I might go out and rich the mix a little. Mainly I'm just happy that I'm not getting 9.5 like I was getting 
. I thought that the stumble that I had under acceleration was a spark issue. Turns out I was washing the spark out with fuel, so so far so good. Just gotta get the little kinks out.
. I thought that the stumble that I had under acceleration was a spark issue. Turns out I was washing the spark out with fuel, so so far so good. Just gotta get the little kinks out.
Laughing Gas
Joined: Dec 2003
Posts: 900
Likes: 3
Getting the kinks out is half the fun with these old things. I was originally planning to convert my truck to EFI, but after getting the wideband and spending some time tuning the carb, I'm pretty satisfied with the way it runs now. Cold starts are even a one tap one turn deal now, and she'll drive away cold almost like EFI.
One thing I forgot to mention is to check the carb owners manual and make sure the accelerator pump linkage is dialed in to specs and there isn't too much slop or play causing the pump shot to come in late. Just a thought.
One thing I forgot to mention is to check the carb owners manual and make sure the accelerator pump linkage is dialed in to specs and there isn't too much slop or play causing the pump shot to come in late. Just a thought.
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Cargo Master
Joined: Oct 2004
Posts: 2,148
Likes: 0
From: Seneca, SC
yeah the thing still blows lean after enriching the mix to 12.5 at idle. Not ideal, and I'm with you that it's the accelerator pump at this point. Also do you think that the squirters might be a little on the lean side? If I get this thing leaned out I'm going to go leaner jets on the mains. It's still at 10.5 under primary load, but leans out to 12.0 (perfection) under primary and secondary. I think that if I can get the accel. pump and squirters to get it fixed then I can do jets. If not then I might have to change out the main side metering block with one from a holley 390.
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