Washing engine

Don't use anything high pressure, and cover up all openings and electronics.  I always just do a gentle "sponge bath", myself.

But if it's really "cruddy" on the outside, doesn't that make you wonder about how bad it might be on the inside?  Hopefully you have replaced all the rubber parts and the fuel pump, at least.

Food for thought:

Common sense has to apply here just like using tools, sealers, cleaners or any maint. you do. Think first and look forward for any unintended consequences. 

If a Rotax was very susceptible to water then you wouldn't be allowed to fly in the rain or there would be no amphibians.

Again use common sense.

What I have done over the last 20 years is I use "Oil Eater" degreaser. It is a water based bio-degradable degreaser. It works like a charm. If you spray it on a greasy area, exhaust covered area or oily area the grease will be running off before you use a rag or rinse it off with water. I wipe the belly of all planes off with it. I use "Oil Eater" on all aircraft surfaces and it won't hurt it. I know of hundreds of people that use it in the aircraft business. Most of the Light Sport guys I know use it and like it because it doesn't cause any damage. That said  I wouldn't use it to wash and soak the entire plane  in it. It won't hurt the engine and then you can just take a hose or bucket of water and rinse it off. It comes in spray bottles, 1 gallon jugs or 5 gallon buckets. I buy the 5 gallon bucket because it works great on dirty hangar floors, planes and even the vent hood above the stove at home. Works really well cleaning K&N air filters. It will not harm the filter. It can be diluted with water if you want. I use a very large used clear plastic Pretzel container. It looks to be almost 3 gallons in size. Buy one with the Pretzels at the store and eat the pretzels then you have an empty filter washer. :)  Toss the K&N into the container, pour in some "Oil Eater" and dilute with about 1/2 water and put the top on and gently shake it and swirl it around. All dirt, bugs and oil are removed. Then rinse the filter out really well and let it sit in the open or in the sun to fully dry and then apply the K&N filter oil. Works like a charm.

If you use a hose to rinse an engine just don't target or spray directly into the rear coil and flywheel area of the engine and don't spray into an external generator. Just stick to the solid metal areas.

Another thing you can use is something like a spray carb cleaner. I use "Brake Clean" to spray up under the crankcase, into the oil / radiator to de-oil them or up and around the cylinder fins. Then rinse it off. Again stay away from the exposed electrical areas. 

p.s.

Thanks Bill for the reminder on the drying afterward.

I forgot to mention either start it up to dry it or use some compressed air.

Jim, your engine has been in storage since 1995?  Have you shipped it back to a Rotax Service Center for internal inspection and required maintenance?

I am with Roger!

Water flowing at under 50 mph is not going to hurt it. Think garden hose Open spray. No pressure washers.
Ideally, after washing you would want to start it up to heat it up and blow it off.
If you are not in the position to start it, at least blow it off with compressed shop air to get the water out of the crevices.
Air is pretty good at drying stuff.  And Again, use some common sense on how hard to blow and what to blow off.
A little goes a long way.

Oh my... I missed this post....sorry.  Good advice so far however the "elephant"  in this conversation is this engine is way out of date.  A check of the database on service bulletins that may be applicable to check number over 50 at this time.  To start with all the rubber parts for 5 year must be changed.  I would return it to a service point and have them do all the SB checks and rubber parts along with corrosion inspection.  

Consider that all the oils inside this engine have long since dried and are no longer giving you the oil coating it did when it left the factory.  The correct way at this age would be a teardown, check for corrosion and relube and retest the engine on a test cell to verify it is still functional.  The carbs would need to have a complete check also as parts are perhaps dry and O-rings and the bowl gasket need to be replaced in my opinion.  

I think washing it is perhaps the least of your concerns before you try to test run it.  Soap is not a good thing on the engine as it may wash out the lithium grease used on all the electrical connections.  As pointed out avoid any pressure washing for sure, that just drives the soap or cleaners directly into your electrical connectors faster.  

The gearbox, crank, camshaft and components of the valve train have perhaps developed rust and this needs to be addressed.  Even cylinder studs have to be changed if they are pitted by rust at this point.  (the pit may create a stress riser and it could fail prematurely) 

Protect your investment, don't cheap out on a good inspection is my view.

Cheers