Beck TD, Part 55: Tom Bryant's SU Carb Tuning Procedure

When I rebuilt the SU HS6 carbs in Beck, I followed the online procedure published by Tom Bryant, who has rebuilt hundreds of sets. It worked great, although I couldn't know it right away because the engine in Beck was in such poor shape. After installing a used engine I procured from Joe Lazenby, I installed my rebuilt carbs and proved that I had done it right.

When I first set them up, I purposely left them "fat" at Cor Engelen's advice - he noted that it would do no harm to be a bit rich, but you could burn a valve if they were too lean. It ran fine, but blackened the plugs after a few hundred miles. I decided today, when PA weather was gloriously warm and sunny, was a great day to tune them better.


Tom's tuning procedure can be found at this link:
https://thosbryant.wordpress.com/2015/10/04/su-carburetor-tuning/
This post doesn't duplicate his work, so you should follow his post for the step-by-step.

His methodology differs from most because he doesn't mess with a Uni-Syn gauge (which is what I was using) nor does he try to precisely lift the damper to mystically gauge whether the RPM sags and returns, or raises and returns, or raises and stays, etc. Instead, he fashioned a gauge out of a coat hanger to visually see that the carbs are balanced, and then adjusts the mixture for maximum RPM.

Since I didn't have a coat hanger in the shop, and I felt like playing with my lathe, I made some shouldered sleeves to fit the top of the carbs, and bent 1/8" steel rod to make the gauges. Here's a photo:

And here they are in place. There's a homemade spring fixture holding the points aligned. There's plenty of flexibility for the rods to move independently:

 The procedure was foolproof to follow. Tom predicted that a test drive after setting would find a flat spot or hesitation that could be cured by enriching the mixture one or two flats. That's exactly what happened, and one flat fixed it. The net result is that both carbs are three flats leaner than when I started - no wonder I was getting soot on the plugs...

The engine is running very sweetly! We'll see if the plugs stay cleaner over time, but today's weather won't hold. It will be spring before the real testing comes.

Continue on to Part 56...