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Discussion Starter #1
I'm using a innovatemotorsports LM2 to check AFR, I have a 12" extention on the header, the o2 sensor is mounted about 3" back from the collector. Motor is a 532ci with a Prosystems 1000 cfm 4150 carb. First time I took the car out, air temp. in the 60's low humidity, AFR was in the mid 10's. Jetted down 8 jet sizes, the best AFR I could get was mid 11's. Talked to Patrick at Prosystems and he said I should'nt have to go more than 2 jet sizes up or down. Brought the car home, checked some things and found the timing was at 29 degrees. Advanced the timing to 32 degrees, went back to the track sunday, temp. and humidity the same, first pass was the fastest the car hes run but the AFR was mid 14's. As I started jetting up the car started slowing down. Last pass I went back to the jets I started with and the car picked back up, ran a 10.427 @ 128.98 mph. Exhaust and plugs are grey car runs strong out the back, not popping like its lean. I do not have a gasket between the collector and the extention, could I be sucking air in at the collector? could it be a bad o2 sensor? Carb was not removed between the time it ran the mid 10 AFR and the mid 14 AFR, the only thing I changed was the timing. Any thoughts?

Thanks, Danny
 

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Discussion Starter #4
Faster than your 10.50 you wanted hey? Nice job! Obviously something is not right, did you try and go leaner to see if the car still went faster? I would believe the on track performance before the meter.
No, once I realized jetting the thing up was not working I just went to the jets I started with which was the fastest pass the car made. By then I was worn out and ready to go home and watch football.
 

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Make sure your fuel system is up to par. Everything to low voltage down track to an inadequate pump or regulator can mess you up.
 
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