I can't agree with your "mechanic". He could be telling fibs.
My single carb, points ignition 447 with the correct Rotax book spec. jets etc, runs beautifully through the whole range in my Rans S4 single seat 'plane. Starts exceptionally well (rumour says better than the later CDI model).
Has done so for over 8 years and a couple of hundred hours.
I regard it as one of the very smoothest and sweet running little motors available. Fuel usage less than 8 litres/hour of 1 part oil in 50. Proper exhaust box with resonance devices ensures the power is there.
Sounds like its running rich...have you changed the cut of valve in the float chamber,
What type of fuel pump do you have...could it be over pressurising....if the fuel pump diaphragm has a small split in it it can cause your kind of problem...lets excess fuel direct into the engine crankcase and floods at lower RPM...have you looked at the pump.
yes complete change of engine and all accesories,also ran a seperate fuel tank and gravity fed direct to carbie,No change,tried 6 different carbies 2 of which are currently on rotax engines a currently runniing fine,tried every thing ?
Tim you seem to have covered all bases with this prob...I was thinking as you said that when you run the motor with the air filter removed and it then runs fine...that would suggest a rich mix issue...you have substituted the air filter haven't you???
Anyway Rotax some years ago modified the carb breather tubes...they used to have 2 separate breather pipes from the carb body....the new modified system used 1 pipe linked to both sides of the carb...with holes made in the lower part of the tube,
It was to do with low and high pressure areas effecting the fuel level in the carb...prob blast maybe,
Just a thought but has you set-up the new or old vent pipe arrangement,
Another thought....I think you have just bought this aircraft....is the area your operating it now a similar altitude to its old operating area...have you checked all the jetting and needles in the manual re your airfield altitude????
yeh all 4 of my carbies have the single looped vent with a hole in the bottom and a hole an inch away on the top(all good) its got me and bert flood rotax stumped?its really getting to me know and really not sure about these rotax engines,supposed to be good?
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