Can Mogas cause excessive carbon build-up?
 

I have just removed the cylinders from my C90 and was surprised to see how badly coked up the rings were. The top ring in three of the cylinders was almost completely seized in and the lower two not much better with a large amount of carbon in the lanes. The engine has only done c.200hrs since zeroed in 2006 and was running very smoothly with no problems that I had noticed. The Isenburg guru suggests Mogas additives might be the cause of the first ring sticking and starting a chain reaction. Anyone else experienced this recently?I've been on Mogas more or less 100% for the last 10 years. Will probably move back to 100LL unless a better solution is offered!

No, it cannot. I do have very strong doubts this is a Mogas issue. How do you lean the C90?

Better take some training on carburettor adjustment, and on leaning (indeed, GtE!). Carbon build up indicates over-lean burn, whatever the fuel. A good way to produce some nice CO, too, helps to be unconscient of your crash.

And please do feel free to believe in gurus, myself prefer to believe the laws of physics and chemistry. Less complicated, too, generally.

After over 1000 hours on 4star, then on unleaded, with occasional avgas when away from home, (and during the interval between 4star disappearing and unleaded being approved,) a top overhaul showed everything to be surprisingly clean on our O200.

Is the C90 cleared for E5?

Rod1

Carbon build up is rarely if ever fuel related.
2 Problems can be :
- The oil not suited for the engine (or at the wrong temps.)
- Running the engine at the wrong temperatures for prolonged time.

Best to invest in some CHT and EGT sensors, run the engine at the correct temperatures, and change to another type of oil.

Did you have low compression leak checks on those cylinders?

Also check that the breather exhaust is in free air so that there is no pressure build-up in the crankcase.

Can Mogas cause excessive carbon build up?
 

Thanks for the helpful replies. There is no mixture control on my installation so leaning not an option. Compression tests before each permit renewal have always been in the mid/high 70s. W100Plus changed regularly so oil not an issue. I have CHT sensors on the rear cylinders. It's possible that an early period of hot running before I developed a technique of reducing power slightly immediately after take-off might have been influential. Apologies to Mogas.

No mixture control on a C90. Is that not unusual?

My C90 had a Stromberg carb when I bought it, no mixture control, just an idle cut off.
It was fouled up, sticking/deformed needle valve etc , so changed for a Marvel Shebler? With a mixture control.
However, plugs run awful black so this thread interests me. I too was taught to leave the red knob alone.

I had an O-200 with a Stromberg carb. The seller had wired the mixture control shut. After some research and discussion with my engineer we dismantled the carb, checked it over and re-instated the 'mixture control'.

It does not work anything like as quickly or obviously as that on the Marvel Schebler.

But it does work! As it manipulates the float chamber level (from recollection) it is much slower, but the EGT does not lie and neither does the tacho. As Step turn states no lovely gray exhaust but quite a reasonable fuel saving and nice clean running.

:confused: That seems to confirm the opening post? Without questioning your authority, I'd like to see it explained, though. And I must confirm I see some blackish deposits in the exhaust of my Rotax912 - but don't you get these with ANY internal combustion engine running on any fuel?

As an afterthought: the opening post was about carbon stocking up inside the engine, not in the exhaust.

And to T/S: apologies, I was not aware there are US aircraft engines with no mixture control.

Thanks! And, err, "rather dirty", yes I confirm!

We've never used UCL, and use 15W50, usually Shell, but rarely Total. Our O200 has had one mid-life top overhaul, and is now well over 2000 hours. Almost all on mogas.
I don't think we've ever flown much above 70F - and NEVER above 90F, but that's our local climate.

That's because the white is a result of lead in the fuel.