Piston Heads OK?

That is a build-up of lead on your pistons. I imagine you switched to Av-Gas due to experiencing vapor lock when you were using auto fuel? You can continue to use 100LL with TCP, however, you will have to do more frequent oil and spark plug changes and you will need to have your gearbox overhauled within the next 500 hours, otherwise, your clutch will be full of lead and other problems will arise. You may also need to remove and clean your sprag clutch if it starts acting up. It may be a good idea to do an OH on your cylinder heads at around 800hrs (maybe less) to clean the lead deposits off your valves, however, you will know when it's time once your leak-down/comps checks start to diminish (valves leaking).

Unfortunately, that's the price you have to pay when using 100LL, as not only is the fuel more expensive than MOGAS but you now have increased maintenance costs.

FYI, there are thousands of Rotax flying around that operate solely on 100LL, so you are not the only one!

Given that I use Decalin my current thinking is 30 hours between oil changes.

New spark plugs every other oil change (they're so cheap!) and clean the oil tank every 3rd oil change.

I'll just have to accept the more frequent maintenance.  

Craig E Maiman wrote:

Given that I use Decalin my current thinking is 30 hours between oil changes.

New spark plugs every other oil change (they're so cheap!) and clean the oil tank every 3rd oil change.

I'll just have to accept the more frequent maintenance.  

Ah! but have you costed out the "penalty" for the routine use of AvGas;

More costly fuel, for no performance benefit - over operating life of engine, likely to be quite substantial additional cost.

More frequent oil changes - roughly twice that of engines running predominantly ULP - Rotax compatible oils are not cheap.

Increased servicing/maintenance  - particularly of gear box requiring "de sludging" and possibly valve seat /stem cleaning.

Cost of "mechanic in a bottle" - use of magic concoctions like Decalin

I would speculate that the potential engine in service life span (not TBO) is likely to be shorter due to lead fowling of piston rings, bearings, etc - costly replacement of engine, dead befor its time?.

Given that my airport doesn't have Mogas (I think there's one airport in the whole state that does) and I really don't want to have to tanker it in, that only leaves using Avgas.

And since I had what was likely a vapor lock issue with Mogas, I'll for be sticking to Avgas.

Most of us just use 5 gallon jugs to bring in auto fuel. Darn few airports carry 91+ oct. auto fuel.