AFR Gauge

I'm planning to run a Rotec TBI on my Jab 3300. Anyone using an Air/Fuel Ratio gauge with this combination? I'm trying to determine where to place the oxygen sensor.

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Permalink Reply by Dave Geiling on June 4, 2024 at 5:52am

I put mine in the horizontal section after the downward 180 and before the connection to the muffler or in my case the straight pipe extension.  The sensor bungs are slightly angled to allow clearance for the wiring from the pipe above.

Permalink Reply by Alan Lutz on June 4, 2024 at 7:50am

Thanks for the response. Any chance you have a photo? Also, what do you lean your mixture to in cruise. I had found reference to an advisory on the net suggesting a lambda of around .8. That equates to an AFR of 11.0. Seems a bit low to me.

Permalink Reply by Dave Geiling on June 4, 2024 at 6:28pm

Unfortunately, I failed to photograph the pipes after the bungs were welded in and sensors installed.  I may get to the airport tomorrow or Thursday and will try to remember to take one.

I have a Mikuni clone carburetor on a 3300.  I will probably move on to Plan #3, a Marvel-Schebler carb later this year.  The main reason for this is the M-S has mixture control, and that future project is why I added the AFR instruments.  So currently, I have a 280 main jet installed that is a little richer than I would like but the 270 jet originally installed resulted in high cht/egt.  I didn't have the AFR instrument installed until after I changed to the 280 jet.  Idle shows around 12, full throttle around 11.5 and cruise around 12.  I know this is rich and probably need to change back to the 270 ( really would like to try a 275 but can't find one.

Permalink Reply by Dave Geiling on June 5, 2024 at 6:38pm

Here is a photo of one of the AFR sensor and bung I put on my Jabiru

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Permalink Reply by Alan Lutz on Thursday

I talked with Paul at Rotec. He highly recommends an AFR Sensor. Suggested a clamp on bung on the tailpipe. 

Permalink Reply by Dave Geiling on Thursday

I used the weld type bung because I was unable to source the clamp-on type for 1 1/2" pipe.

If you are going to use a Rotec unit I would be extremely interested in the results.  I have the Rotec electronic ignition and their alternator installed and am very pleased with both.

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