912s hard starting

Check your timing. 95 burns too slow. Try a mixture of 50/50 with 87. This might give you the proper burn with the added properties of the 95.

Ron 97 is stated as minimum requirement for the S version so it would not hurt to get a fuel that is slightly higher in octane.

As far as I can tell the AKI 87 is LOWER in octane than the RON 97 so I am at a loss as to why other post mentions mixing your 97 with AKI 87

Your S version has a higher compression ratio and may start a bit harder but it should not have real problems. It cannot hurt to check the basic settings.

Octane is a function of burn speed. The higher the octane number the slower the fuel with burn in the cylinder.

Why do you argue with me rather than fix the problem with the original post. If you are so smart fix IT!

I don't think he is arguing with you, just explaining, to the point, of exactly what the differences in octane rating are and how they likely would affect engine performance. The question I have is, because this is a cold starting issue, does octane rating affect vaporization rate. If so , and IF 87 vaporizes faster in very cold weather starting conditions (I don't think so), would it be allowable to start the engine on 87 and switch after a low speed warm-up. This might require a second very small fuel tank. In racing, they use octanes of 103 to 117 or so, depending mostly on RPM range. A fuel supplier told me that in addition to controlling flame front propagation, high compression racing engines that live at 6000 RPM's and up require a faster vaporizing fuel to eliminate droplets that also lead to detonation. Of course, these formulations cost money (3 to 4 times the cost of pump gas) and aren't readily available on every street corner. For small, recreational aircraft use, purchasing a couple of 30 gal. cans of Cam 2 or VP (Vels Parnelli) or Sunoco or other racing fuel isn't difficult. I don't think it hurts an engine to use a higher octane fuel than required. And racing fuel burns cleaner as well as a hole in your pocket.

Here, in winter, we sometimes use a fuel line anti-freeze (methanol). I have found that when I use it, 0 deg F starting seems a bit easier, but then I don't have a high compression engine to worry about. I always carry a can of starting fluid (ether) just in case I sense flooding or just don't want to wear down the already half frozen battery and save wear on the starter. I even installed a two foot piece of 3/8" PVC extending from the front grill into the air intake duct so I don't have to open the hood. I know that high compression engines and ether don't get along well. You should never use it on an all out race engine although the NASCAR guys will use it to get re-fired during a race where everything is on the line.

By giving correct replies to wrong answers I AM HELPING original poster.

If you dont like to be corrected maybe you should make sure what you post is correct or state you are not sure yourself.

Well put case, I gave you a GA. Your opponent (mayt2u) is totally wrong and off base....basically he has not got a clue!!!

This sort of reply is uncalled for, you described it completely wrongly and could seriously mislead others.

I agree with Case completely (for a change says Case!!)

We have had our discussions here Andy, In the end we either agree or we agree to disagree.

I respect your input as I recognise you tend to know a lot about what you like to post about and you post a lot about what you know.

You are right there are some people who forget that information is just too easy to obtain these days and will stick their NOSE in too soon.

Keep up the proper written language now, no foulmouthed insinuations here please

Thanks for your support, much appreciated.

You deserved support in this particular case, I gave it.....its that simple.

Have a great day.

Not to mince words but Octane rating is not percentage of isooctane. Isooctane is merely the std that is "set" to 100 octane rating. Fuels with 100 rating are still very diverse mixtures, but have detonation character same as iC8.

More detail from Wiki http://en.wikipedia.org/wiki/Octane_rating

Octane number is the number which gives the percentage, by volume, of iso-octane in a mixture of iso-octane and normal heptane, that would have the same anti-knocking capacity as the fuel which is under consideration.

It does not appear to be fuel as does the same on av gas. It seems as if the engine is to far advanced a LAME has set it up to the specs still does it.Have even installed a higher capacity starting moter to wind over faster. Starting to think it has something to do with ignition system.This does not happen on mates 912 starts instantly.

Odd problem, I would think it would be worse when hot rather than cold. Personally, I'd check spark plug gapping. If that's ok, I'd set the timing back a bit and see if the problem went away. Does a Rotax use mechanical or electronic ignition? If mechanical you may have a jammed centrifugal advance. Or the same thing in the electronics. This will cause it to be over advanced while starting but be ok while running. A bad vacuum switch might be a possibility.

I have worked on a few 912 and 914s. Most of them have to meet a certain rpm and oil pressure then the ignition will fire. plus leading to the fact that usually aircraft batterys are ususally on the small side add cold weather and it makes it hard to start. so make sure your using thick starter cables and a charged battery, you can usually tell because adding a second battery usually starts them up.

also join rotaxengines-list on this site http://matronics.com

As with any engine, if it kicks back while staring, it is generally a problem of ignition timing.

Any engine will start on the wrong Octane with no problem if all other points (pun intended!) are otherwise correct. Running on a lower Octane is of course another matter....

Having an over advanced ignition (which is similar in effect to a too low Octane fuel) can lead to mild or worse overheating as well as higher than normal wear on certain parts......its certainly not to be recommended.....so take the problem really seriously.

Sorry boliver, yet wanted to help. Up North we mix all kinds of fuel to get things to run in the cold. We don't have the luxury of having the best temperature in the Southern US to do our testing, just the Great White North. We have engineers that quote scales, charts and other dibble, that one wonders if they really know what they are talking about or just like to hear themselves talk.

Best of luck on the situation and I will no longer subscribe to CR4 if is this the kind of treatment I will receive.

My impression is that you can "give it", but not "take it".

If true, then CR4 is really not for you at all.....you have to be able to "give and take" on CR4.....

I have a Hirth F-30 (4 cylinders) and it was nearly impossible to start. I put a centrifugal clutch on it, and it starts right up...and it allow me to idle without the prop turning while on National Park lakes...a big plug around docks.

The torsional resonance between the engine and prop via the rubber donut did not allow the engine to come up to speed. Without the prop engaged in the low frequencies of startup, the engine could function.

The clutch mod cost me around $700.00. It made all the difference for my seaplane...

Thanks for input so far it appears that it is not a fuel issue, talked at a local club meeting last night & sugested to start with big battery & calbes as timing is set in factory for these motors.

Do you (or anyone else) know of a way to check that the timing is still right?

Is it possible that someone has accidently, removed/replaced an item that affects the timing?

Is it possible that the "unit" that performs the timing (?) is defective and has lost its method of working properly with regards to an advance/retard mechanism (for want of a better word)?

It may sound strange but I once had a Honda........yes really

It had factory set timing as well by means of the old magnetic pick ups on a disc that was set in the factory with the rotor whizzing past inside it. What had happened was that somebody in the past had thought the whizzing magnets had to touch the pick ups and set them so they actually scrapped the surface. This is wrong of course and there should be an air gap of a given size depending on the make of the unit.

The end result was that the coils had shattered inside without any visible damage to the outside but they now had a "fuzzy" field of pick up strength rather than the accurately determined point they need for proper function. My timing was all over the place and the bike did not run very well if at all depending on the ambient climate at the time.

Maybe your unit has had the same misfortune? Worth a check unless the engine is nearly new.

I gave you a GA.

But you are boring the arse off me with your good answers, can you become "provocative" or something to liven things up?