All Small Six Tuning with AFR gauge need help.

[ActionYobbo]

First time using an AFR gauge was on this motor. Totally stock 200 with large log head autolite 1100. So first up the jet was 70 and AFR reading was 10.0 so I went to a 67 jet and AFR was 10.8 to 11.2 so I went to a 65 jet and AFR is 11.7 to 12.0
65 is the smallest I have now but the book says 66 for this motor but I am also running 89 octane with 10% corn. I read I should be trying to get mid 13’s to low 14’s as a good AFR but I think I am getting too lean now. Am I chasing the wrong AFR? Is 12 ok? What am I missing?

 

[vssman]

I’d stick with the 65 jet although it is a little fat. Being a tad rich is better than too lean.

 

[gb500]

Are. Your readings at full throttle accelerating so its running on main jet and 'power valve 'is open

 

[ActionYobbo]

12 at idle
12 driving around the parking lot
11.7 wot from standing to 50
12 no throttle slowing down C4 automatic

 

[alwill923]

Still too rich! Get smaller jets and check the spark plugs. At least go with the 66 as indicated.

 

[awasson]

Where did you install the oxygen sensor? is it 6" - 8" after the collector or after the manifold on a straight section of pipe? Also, what leads you to believe it's getting too lean if the gauge says it's still a bit rich? Do you think the tune improving or not with the changes in jets and what's the engine temperature like?

I found this article that seems to indicate that although 14.7 is ideal, 12 makes the most power. I think that's probably relative to the type of engine but it's promising: https://www.teknikmotorsport.com/te...t=All it knows is that,1 makes the best power.

 

[Frank]

Perhaps verify your gauge is calibrated right by leaning out the idle mixture and see if the gauge follows.

Some brands of AFR require recalibrating the O2 sensor every so often by removing it and waving it around in the air.

 

[ActionYobbo]

I will pull some plugs tonight and look at them. I never got this deep into tuning up an engine. I had a guy (K) who would do this for me in exchange for welding but cancer got him so now I am learning where K would have done this in one afternoon I am counting the days.
My main reason for asking this question is 66 seems to be the go to jet size and I am at 65 and it’s still rich by the gauge readings. The sensor is 11 inches from where the pipe joins to the cast iron manifold. It’s got a 180 thermostat and the temp gauge is near hot.

 

[Frank]

I will pull some plugs tonight and look at them. I never got this deep into tuning up an engine. I had a guy (K) who would do this for me in exchange for welding but cancer got him so now I am learning where K would have done this in one afternoon I am counting the days.
My main reason for asking this question is 66 seems to be the go to jet size and I am at 65 and it’s still rich by the gauge readings. The sensor is 11 inches from where the pipe joins to the cast iron manifold.

Understood! Be patient- engine knowledge is very rewarding, worth the learning curve in the end. I'd leave the jet and do something to lean the engine up till it runs rough. Idle mixture screw I mentioned. You could pull a vacuum line or two till it's idling bad and check the gauge. It should be in the high 15's at least. Check the plugs first, if you're going to do that.
What brand AFR gauge?
What's your altitude?
Was it running well before the the jet change?

 

[ActionYobbo]

Elevation is 1250
It was running but it was never right. It felt dead and would pick up rpm as I eased off the gas like it got the right mix for a few seconds. Tail pipe was black and plugs were black.

Edit for pictures
Last time I had the plugs out was with the 70 jet and they were black. Since then it’s done 40 miles with a 67 jet and 4 miles with the 65 jet + idle and such for adjusting idle etc