Rotax 447 lose rpm

[Guest funcher]

Hy all. I need your help:

 

I have Rotax 447 engine (http://www.ultralightnews.com/rotaxinfo/rotax447.html)

 

My rotax 447 engine losing rpm from 7000 to 4000 rpm in the flight and on the graund is the same problem.

 

When it lose power till 4000 rpm, after few minutes engine reach again 7000 rpm. I check fuel system and carbourator- all is OK. Pistons and spark plugs is OK. Compresion into engine is normaly. Engine starting normaly but can't keep 7000 rpm. This probelm are with/without propller. Nothig changing. Temperature gauge of engine don't work.

 

I have a fell that engine want to die, when it lose power!

 

I had checked spark plugs- color is OK. The fuel level in carburator is OK. I was cleaned air filter and fuel filter and also carburator inside. Today I was called to mechanic- He told that engine don't start! After special oil use in air filter the engine start normaly. (looks like compresion problem I think. What do you think?) My engine have Mikuni fuel pump, it's work normaly. My mechanic was tryed to drive on the graund by my airplane and was observed rpm loose. Give full gass -> after few min. loose power -> after few min. power comes back. = all time he holded full gass = NO RESOULT.

 

P.S Sory for mistakes in gramatic, Funcher.

 

 

[billwoodmason]

Hi Funcher,

 

It might be worth checking the crank case seals. If they leak the fuel cannot be drawn in to the crank case.

 

Cheers,

 

BW.

 

 

[Sapphire]

I had a 447 a while back. Needed lots of priming to start cold even using the "choke" which was actually an enricher valve-one way was to saturate the air filter with fuel but a better way I drilled a small hole in the metal end of the air filter and with a long tube attached to a squeeze bottle injected fuel into the carby. Even then on real cold mornings, you needed a few trys and injections before it would run continuously. Also, the needle in the carby can come loose and drop down closing off the high speed jet leaving the engine on idle. A modified clip and some o rings from Rotax need to be installed. Could be causing the wild rpm's. These carby's don't have carby heating and icing could cause that as well. In fact a 503 Rotax went down with the same problem and no reason could be found. Ice probably was the culprate and would be gone before any investigation. Some pilots wrap a heating coil around the carby [like an electric blanket] Also, replace the fuel pump. An overhaul kit is cheap. It's just a piece of plastic with some flaps cut out. The carby is simple to take apart and blow out with compressed air. Replace the fuel level valve-needle and seat. Make sure the plunger connected to the throttle cable runs freely and the throttle cable works ok. Also check the idle and high speed jets which just screw out. They get a deposit on them so clean them out with soft plastic. Adjustment of the competed carby is simple You really are overhauling the carby and a publication on how to do it is available-maybe free on the internet, can't remember

 

 

[Tomo]

G'day! Have you checked your exhaust system at all? If there is a loose baffle or something floating around inside restricting, opening up the flow it will cause problems.

 

Also is it single or dual CDI, or points ignition? twin or single carb?

 

I've got a single CDI single carb 447 in my plane and it will hand prop start after five swings of the prop, or with the electric starter pretty much straight away! Make sure also, that the little fuel pump that runs off the crankcase is working.

 

 

[planedriver]

Have you checked the breather hole in the fuel cap is not blocked?

 

Maybe try it on the ground with fuel filler cap loosened to make sure it's breathing ok

 

Rgds Planey

 

 

[Guest funcher]

Sapphire- My carburetor also has special warmer. My engine haven't problems with leaking fuel. My first fuel tank is mounted top of the engine. The fuel sneak out of the pipes normaly. (unmonted the pipe from carburetor) Mechanic told that my fuel pump is mounted only for second fuel tank, who must be under seatplace and under engine. (I haven't) I use only first fuel tank and fuel pump also working. So we wasn't detected the problem in fuel system, becouse all working nice.

 

Tomo- With exhaust system all is OK. Not sneak of smokes. I have ROTAX 447 air cooled by fan, single BING slide carb, rewind starter only, Mikuni fuel pump, BOSCH magneto ignition 12v 140 w, two stroke otto engine. And Engine sound is OK. When the engine is warmed than it starting in first time. But when it is cold, than I unmount air filter and than I put fuel stright in carby. Only than engine starting good. I was drived on the graund by half of power and all was great- RPM was till 4.5 rpm. But when I was tested it on full of power, my engine reached 6.5 rpm and after little time it loss power till 4 rpm and rpm don't going up anymore. :( Next week I will take new compression tester and I will again check compression. Left only two reasons of engine power loss: Problem with pistons, piston rings, or cylinders. Or problem with ignition coil. Maybe someone can give me info- what problem may have this bosch ignition? Did ignition problems can be the reason of rpm lose?

 

I have mounted on type B gear box 1600 mm propeller, but for my engine need propeller with 1400 mm. Did this too can affect rpm lose? (wood propeller) Where is the difference of propeller size choice? Maybe this propeller make biger vibration on engine, but I can't feel it on my body.

 

Thanks all for help.