I know you have ruled out ignition, but have you checked the plugs? What condition are they in? It might be worth changing the plugs to new ones, you just never know.
Yes. They have been checked (and are checked every 25 hours).
I did read an article the other day about fuels. Here in the Philippines we can only get 100 Octane Blaze. (It is the only fuel available her without ethanol additives.) The articles suggested that this might not be great for Rotax 4-stroke engines. Any ideas about this? Does anyone have any problems starting engines when using high octane fuels. Maybe I would be better using a 95 Octane fuel with 10% ethanol?
If you are still idling at 1200, that is much too slow. Turn the idle up to +/- 1800RPM and the starting problem may disappear. Airboats and seaplanes try to keep the idle as low as possible to avoid moving at idle. 1200RPM at idle is bad for the Rotax gearbox and engine. Large engines with low compression and no gearboxes like the Lycs or Continentals can idle slowly; not a Rotax.
I can almost guarantee that if you service your gearbox and get it re- shimmed, and increase your tick over to around 1700- 1800 rpm, your problem will disappear.
Getting the idle rpm set up to 1700-1800 rpm will help on your starts and keep from beating up your gearbox.
Unless you have done a slipper clutch friction torque test on the gearbox and it shows low it doesn't need to be re-shimmed. Re-shimming is done if your gearbox friction torque is low. If it is low then you may be experiencing kick back at the prop during stat up. Fix the idle rpm first. Make sure the choke circuit is not engaged after it is warm when you try to re-start. Normal and average friction torque is usually between 440-485 in/lbs.
Roger Lee LSRM-A & Rotax Instructor & Rotax IRC Tucson, AZ Ryan Airfield (KRYN) 520-349-7056 Cell
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