Sven den Boer wrote:
> <svendenboer@quicknet.nl>
>
> During take-off power no problems, at throtlinging back
> 200-300 rpm at 700 feet, the engine starts to run rough
> for 1-2 seconds, as if it's running on 3 cylinders,
> thereafter no observations. Engine has been checked by
> Rotax dealer on ignition and carb balancing, nothing
> found. Any suggestions ?
>
This sounds like the problem I had which took me 9 months
of fiddling to solve.
The fuel pipe to a carb (port in my case) was too close to
the exhaust manifold and the insulation around it melted,
allowing exhaust heat onto the pipe, The stainless steel
covering then conducted the heat up inside the insulation.
Firstly change the direction of the banjos on the carb.
Point them rearwards to keep the pipe away from the
exhaust. If this makes a difference arrange to get some
new unions made up (straight ones) so that the pipe can be
re-routed over the top pf the carb rather than underneath !
This solved it for me. Rotax firmly refused to believe
that this was the problem, but the fix solved it so I am
content with my solution !
While at full power there is plenty of fuel flow in the
pipe, the exhaust gets hot, but the flow is sufficient
that the heat doesn't affect the fuel. When you ease off
the fuel flow reduces butt the exhaust is (initially)
still hot so the fuel vaporaised and you get a misfire
until the exhaust cools, the fuel cools and then it is OK.
2 -3 seconds is about right !
Richard Holder who got really frsutrated with this, trying
everything, but then had a lateral thought and found this
problem.
HTH
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