PT20J

I was speaking of the factory installed tachs.

I didn't like the Saf-Air valve. The low flow is caused by not fully compressing the stiff spring. To get good flow, I had to lay on my back to get enough leverage to compress the spring. I found some new/old stock MDI valves (F-391-53S) on eBay. I haven't tried the Curtis valves.

From the M20J POH: M20J POH

McFarlane Curtis CCA-53 $27.03

Paul @kortopates would be knowledgeable on this engine You could try fine wire plugs. The "mixture" in the cylinder is never homogeneous; there are swirling pockets of mixture with the right combination to light off surrounded by areas that are too rich or too lean to ignite. Fine wires, by virtue of their construction, place the spark deeper in the combustion chamber than massive electrode plugs and more easily ignite lean mixtures. The extended electrode BY plugs do the same thing (at much lower cost than fine wires, but require gapping and don't last as long) but not all engines have the clearance to accept them.

If it is a B&D electric tach then it is driven by a tach generator on the back of the engine accessory case and would be independent of the magneto.

How lean are you trying to run? What you describe is pretty normal in my experience when running too lean. Every once in a while a cylinder will be lean enough for a few of low power cycles to cause enough power loss to be noticeable. The low power output for a cycle is a random event, and so over time, the laws of probability state that there will be several low power cycles consecutively. If that happens, just enrich a little bit.

"Smoothness" is relative. No two combustion events in a cylinder are quite the same -- it's a chaotic process. So, there is always cycle-to-cycle variation in cylinder power output, which causes some roughness. The variation increases as mixture is leaned -- that's why it gets really rough if you lean too much. So, any given engine will always run smoother ROP. But, if mixture is nearly equal in each cylinder, then most people find a level of LOP operation that's "smooth enough." Also, it helps to have more cylinders because you get more power pulses per revolution. My little Lycoming four banger will never be as smooth as @PA24Lvr's monster engine .

I think all the 2-1/4” tachs are electric and the 3-1/8” tachs are mechanical. Mechanical tachs are driven with a speedometer-type cable. They need to be lubricated every so often or the indicator gets jerky. You can unscrew the cable from the rear of the tachometer and pull the core out of the sheath and lube it with speedometer cable lubricant from an auto parts store. Troubleshooting the G3 would begin by determining what kind of pickup it uses.

Winds aloft is the biggest variable.

If it is just leaking from the screws, you can run the tank down below the level of the screw and use Permatex 3 on the screw. If you need to stop a screw leak some where you can’t drain the tank, EZ Turn will work.

The o-rings can take a set and allow grease to leak out. It will accumulate on the inside of the spinner near the blade openings. This can often be fixed by deep cycling the prop several times. It might take doing this during runup a few times. From the McCauley Owner/Operator Information Manual:

I once owned a car with white seats. I spent a lot of time cleaning them.

Fuel is leaking somewhere. You’ll need to find out where to determine how to fix it. If the boots that seal around the holes where the landing gear push pull tubes enter the wheel wells are not in good shape, the increased air when the wheels are down might be what’s increasing the smell. But the root cause is still a leak somewhere.

I don’t see them listed for that wheel, but I may not have the most current documentation. Try searching for Cleveland molded seals.