308 Carb tuning with O2 meter

After re-building my carbs I took the time to synch and get the idle settings perfect. This is fairly easy to do with the car standing still but getting the tuning perfect when running on the road is a little harder. To this end I borrowed from a friend a really cool tool made by Innovate Motorsports. It is the LM-2 wideband O2 meter with a fitting to read the exhaust mixture via the exhaust pipe. Here is a product link to those interested: https://www.innovatemotorsports.com/products/lm1.php

With the tool in place I could do driving runs and record the results or (in my case) have a friend ride along and call out the AFR readings at different throttle applications, loads, and RPM's. With a handful of jets at our disposal we could quickly make changes and see where the air fuel ratio could be improved. The whole tuning process took a couple of hours and made a huge improvement in general driveability and throttle response. The exhaust now burns clean and the engine has more pull than ever.

When tuning we targeted AFR numbers in the low to mid 12:1 ratio up to about 4000 rpm and a slightly leaner mid 13:1 at upper RPM ranges for cleaner and crisper burn. All very safe ranges that will not harm the engine. Slightly richer up top maybe would yield a little more ultimate power but I liked keeping the exhaust clean and the throttle response sharp so we went for the slightly leaner setup at higher rpm.

To be as accurate as possible we did all of our on road testing with the full airbox and filter in place. It is more work but will accurately replicate real world driving conditions. Great fun and I would recommend O2 tuning to anyone.

Here are some pics of the procedure:

Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login

 

Idle mixture and sychronization was done using the methods already widely practiced. I did not have an exhaust gas analyser for the idle mixture so I tuned based on richening the mixture until the cylinder cut out and then backing off from there. Having done a number of other cars I felt very comfortable in the procedure and feel that the results are very accurate. As for the on road tests we experimented with both one and two O2 sensors and in different pipes before coming up with our final setup. We found the clamp on O2 sensor to not give good readings at idle because of the tendency to suck air back but as soon as the revs climbed a little the numbers became very stable and predictable and the way the gauge performed gave no reason to doubt the accuracy of the measurements. That said I agree for the best idle measurements a weld on bung with an O2 sensor before the muffler would be best.