Adjustable main jet

[joe_db]

I can't recall seeing a post about these in forever.
I was thinking of adding an oxygen sensor port when I redo my exhaust and getting the adjustable jet.
Are these still a good idea?

[Al Schober]

I like the adjustable main jets. They're adjustable!
Having an annular orifice rather than a round one, the passage is smaller for the same area and is more sensitive to clogging. But when it does clog, screwing the needle out/in usually corrects the issue without major work.

[Dave Neptune]

Joe, the last one I remember playing with the adj-jet and an 02 sensor was Hanley. I do remember he would have to adjust for various cruising speeds.

I used the adj-jet only to find the weaknesses in the carb metering. Once I figured out the adjustments the carb needed I changed the main jet and the air corrector as well as the float level. I then did away with the adj-jet as I don't like the possibility of an additional fuel leak.

I did the above with the Indigo prop, Indigo EI installed and made a gain of 150RPM's as well as a noticeable gain if fuel economy. It would idle all day in or out of gear and never fouled a plug with one very low compression cyl and another down a little but from the other 2. The adjustments were a leaning process and it took a few extra seconds to start. Ran for over 20 of the 34 years I had her in this manner.

I did not use an 02 sensor just the tach, vac gage and plug color for the changes I made.

Dave Neptune

[edwardc]

Years ago I followed Hanley’s lead and installed an O2 sensor. I liked the certainty it gives me adjusting the idle and main jets. I tend to set the idle mix slightly rich to ease starting, with the adjustable main spot-on the proper mix.

Mounting was trivially easy, as I have a Moyer manifold, and the block-off plate for the unused port makes a perfect site. I simply bought a spare plate and drilled and tapped it in the shop. This way the process is easily reversible should the need arise.

[joe_db]

I replace my riser every few years instead of waiting for it to rust out and surprise me, so I was thinking of drilling an O2 sensor hole in it next time I swap out.
My plugs are pretty decent, so I don't expect to find the mixture way off, but you never know until you measure it.