247 not accelerating.

by Joseph A Miller in 2 Stroke Technical Questions 2 years ago

Hello all!

I am having a very frustrating problem with a 1980 somthing rotax 247 single mounted as a lift fan for a hovercraft. I bought the craft with this problem and thought I could figure it out. I can get the motor to idle, but not accelerate unless the throttle is moved very slowly. I have rebuilt the original tillotson carb, tried 2 others with the same issue. I have rebuilt the engine completely with new gaskets piston etc. I have set the timing to spec.I get reversion through the carb when I try to accelerate and when at speeds above idle.

Please help! I am going crazy trying to figure this out.

Thank you

Joe

Page 1 of 2

Start
Prev
1
2
Next
End

Re: 247 not accelerating.

by Dennis Richardson » 2 years ago

Dennis Richardson

1 153 169

Is there a restriction in your exhaust system?

Report
Re: 247 not accelerating.

by wayne beyer » 2 years ago

wayne beyer

3 30 38

I would check the exhaust

Report
Re: 247 not accelerating.

by Joseph A Miller » 2 years ago

Joseph A Miller

1 2 3

I removed the exhaust to check and still have the same issue, no improvement.

Report
Re: 247 not accelerating.

by Dennis Richardson » 2 years ago

Dennis Richardson

1 153 169

Is the fan constantly engaged? If so, then was it designed for this 2 cycle engine? It maybe that it is just to heavy of a load if it was designed for a 4 cycle engine that operated at much lower rpm.

Report
Re: 247 not accelerating.

by Joseph A Miller » 2 years ago

Joseph A Miller

1 2 3

Yes, this is a lift fan, and the fan is driven directly.from the crankshaft. This is the original engine, and had around 80 hours of use. Unfortunately I do not know the reason or circumstances that caused the problem. When I tried the last carb and was getting frustrated, I did remove the fan assy. That only mildly improved the problem. I have a running 299 coming this week or next that I will swap with the 247. I will tear the 247 back apart and look for any issues. I am betting in a timing issue, or case leak.

Report