912 ULS starting but stalls

Sean Griffin wrote:

That's terrible Jeffrey.

Just wondering about the fuel additives that you are using "Lucas octane booster & Stabil" - What do you hope they are doing for your fuel/engine?😈

I have used stabil in my small engine gas for 30 years in hot, humid Florida. Yamaha, Honda, Echo, Suzuki, Still, Black Max, Briggs & Stratton, Toro, Shindaiwa, Rotax 582, Sears Craftsman. What does it do to a Rotax 912ULS that it does not do to any other engine I have used? 

Lucas is an octane booster used by lots of Rotax owners, according to multiple searches I did on this site when entering the aviation world five years ago, to bring up common 89 octane to 91 needed for many Rotax engines.  Lots of folks in Alaska use it as at times their fuel is a bit older than us that are closer in the delivery scheme.

I have been told to not use E-0 or any automobile gas in a Rotax.  Now why would I, an American, in Florida, have to worry about using my readily replenished fresh fuel in a Rotax whose manual states it as a recommended fuel?  It is not more than a month old before it is relegated to the motorcycle, outboard, car, truck, lawn mower or chain saw.  P.S.  I don't use my chain saws often and with stabil and 2-stroke oil in the can it has been up to 2 years before the can was empty and I have not had any problems.  

Of course I would not do that in my aircraft.

My 32 year old Toro, 2-stroke mower had a cleaner carb bowl than my 25 hour Rotax did.

Jeff Blakeslee wrote:

I believe that the Lucus Octane Booster effective ingredient is MMT (Methylcyclopentadienyl manganese tricarbonyl), about 5%, suspended in naphtha. It is marginally effective at doing what it says, but can cause fuel system and engine deposits. I would not use it in my aircraft engine. 

I read that too and stopped using it after the second 200hr carb service.  

Can you reason that that greasy, slightly gritty, gray goop on the idle mixture screws is deposits caused by Lucas?

I am really sorry I did not save it to be tested instead of cleaning and moving on.  It never recurred after that first finding before the ~25hr inspection/cleaning I did. 

But thread drift and complaining aside.  I will get to the engine after I finish with the project of moving my EFIS to another position.  Something to finish before trying to start it again after "one change at a time". 

Guday Jeffrey,

With the exception of my diesel equipment, I do not use fuel additives (happy to expand on the diesel additive reasoning if you want).

I get quite confused with the USA petrol supply market.

After spending two winters in Canada, I do understand winter/summer grades -  let's not discuss this difference

In Australia we have automotive petrol in  91, 95, 98 Research Octane Number (RON) 

We also have Ethanol 10% blend with petrol (E10) which Rotax allows, with the proviso that the airframe manufacture approves.

Rotax advise using minimum 95 RON however in recent times indicate a preference for 98 RON (better knock resistance).

I use, almost exclusively, 98 RON in my Rotax and 91 RON in my small 4 & 2 stroke engines (of which I have many).

"It is not more than a month old before it is relegated to the motorcycle, outboard, car, truck, lawn mower or chain saw."

Is this a comment on the "shelf life" of the fuel?

Can't comment on US petrol, here we understand that 98 RON degrades a bit faster than 91 RON.

98 will keep "fresh" for about 6 months in a sealed container that is 75% full, or better  - no need for fuel stabilisers

An aircraft fuel tank is open to atmosphere, so the fuel within is likly to lose some of its volatile fractions quite quickly. To manage this, we refuel/top up, just before flying, with fresh 98, which has the effect of replacing almost all of the lost volatiles (no need for octane enhancers).😈

Jeffrey Schinkel wrote:

Jeff Blakeslee wrote:

I believe that the Lucus Octane Booster effective ingredient is MMT (Methylcyclopentadienyl manganese tricarbonyl), about 5%, suspended in naphtha. It is marginally effective at doing what it says, but can cause fuel system and engine deposits. I would not use it in my aircraft engine. 

I read that too and stopped using it after the second 200hr carb service.  

Can you reason that that greasy, slightly gritty, gray goop on the idle mixture screws is deposits caused by Lucas?

I am really sorry I did not save it to be tested instead of cleaning and moving on.  It never recurred after that first finding before the ~25hr inspection/cleaning I did. 

But thread drift and complaining aside.  I will get to the engine after I finish with the project of moving my EFIS to another position.  Something to finish before trying to start it again after "one change at a time". 

Jeffrey

No I can’t make a direct connection between the gunk in your carburetors and either of your fuel additives.  In fact, most of the concern about MMT is combustion deposits that are typically a red brown color.  The grey sludge you describe is typically just from old stale fuel varnishing.  Sitting unused is one of the hardest things on an aircraft, and if that is going to be the case, you need a program to cycle out old fuel and drain the carb bowls before extended periods of non operation.

Sean Griffin wrote:

Guday Jeffrey,

With the exception of my diesel equipment, I do not use fuel additives (happy to expand on the diesel additive reasoning if you want).

I get quite confused with the USA petrol supply market.

After spending two winters in Canada, I do understand winter/summer grades -  let's not discuss this difference

In Australia we have automotive petrol in  91, 95, 98 Research Octane Number (RON) 

We also have Ethanol 10% blend with petrol (E10) which Rotax allows, with the proviso that the airframe manufacture approves.

Rotax advise using minimum 95 RON however in recent times indicate a preference for 98 RON (better knock resistance).

I use, almost exclusively, 98 RON in my Rotax and 91 RON in my small 4 & 2 stroke engines (of which I have many).

"It is not more than a month old before it is relegated to the motorcycle, outboard, car, truck, lawn mower or chain saw."

Is this a comment on the "shelf life" of the fuel?

Can't comment on US petrol, here we understand that 98 RON degrades a bit faster than 91 RON.

98 will keep "fresh" for about 6 months in a sealed container that is 75% full, or better  - no need for fuel stabilisers

An aircraft fuel tank is open to atmosphere, so the fuel within is likly to lose some of its volatile fractions quite quickly. To manage this, we refuel/top up, just before flying, with fresh 98, which has the effect of replacing almost all of the lost volatiles (no need for octane enhancers).😈

I understand about fuel degrdation over time. Hence the long tale of relegating the fuel to other engines was indeed a comment on shelf life.

I store in sealed containers over 75% full at all times.  The only fuel stored with lower percentage is my premixed 2-stroke gas for chain saws and the 35 year old Toro.  I normally empty my containers fully at any given fueling time.  If I mix a gallon of 2-stroke that container is used next. Certainly not more than a few weeks.

I do not believe fuel has been left in my aircraft tank any longer than 35 days since new. Sugeries, hospitalizations and such, you know....😕

We use the R+M/2 methodology of lableing fuel here in the US. This relegates Rotax fuel here to the 92. Some unleaded E-0 gas here is only 89. Octane booster is then added. What we have nearby now is an outlet with E-0 rated 93.  Very popular locally and refreshed/refilled by the tanker quite often. Many small engine owners know not to run E-10, especially in seldom used, small motors as bad effects of all sorts are quite common.

When I took training there were two instuctors who used this E-0 89 and added octane booster. Never any problems they said.  So I took their advice.  One did have a fuel injected motor though.   Now, multiple Rotax powered aircraft owners at my home airport use it exclusively. 

About the battery.  I feel ruling it out is justified since the engine fires immediately and runs as it used to, till 3-4 seconds is up.

Is there a way to speed up the idle decrease "kick in" time?