912ULS difficult start since circlip SB

I have to ask... where on earth do you find 95AKI unleaded?  Is it an ethanol blend?

Hello Des

Make sure your fuel pump drain line is routed into a Ram-air and vacuum-free zone. The drainage line must not be routed into the slipstream. Ram pressure or vacuum impair the fuel pressure. (See attachment)

 Here is the Rotax installation manual link https://www.rotax-owner.com/pdf/IM_912_Series_ED2_R1_E.pdf

- 73-00-00 Page 10A (Fuel Pump)

Also, make sure your piston slide is positioned correctly! Since this portion of the carburetors was disturbed, it's possible the piston slides and the rubber diaphragm are twisted (See attachments) 

Here is a video on how to properly assemble the carburetors - https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/311-4carb-ins192

Tyler Hathaway wrote:

I have to ask... where on earth do you find 95AKI unleaded?  Is it an ethanol blend?

Hi Tyler, in Australia motor gasoline is advertised using RON not AKI. The unleaded fuel I use is ethanol free. Cheers

Rotax-Owner wrote:

Hello Des

Make sure your fuel pump drain line is routed into a Ram-air and vacuum-free zone. The drainage line must not be routed into the slipstream. Ram pressure or vacuum impair the fuel pressure. (See attachment)

 Here is the Rotax installation manual link https://www.rotax-owner.com/pdf/IM_912_Series_ED2_R1_E.pdf

- 73-00-00 Page 10A (Fuel Pump)

Also, make sure your piston slide is positioned correctly! Since this portion of the carburetors was disturbed, it's possible the piston slides and the rubber diaphragm are twisted (See attachments) 

Here is a video on how to properly assemble the carburetors - https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/311-4carb-ins192

 

Thank you,

Re the fuel pump drainage hose, the Rotax Owner forums have been a great source of knowledge. The original plastic hose was in the slipstream & operation was perfect for the first 20 hours. When the issue started, the plastic hose was replaced with "fuel injection" rubber hose, no change, then the open end of the hose was trimmed to 45 degrees to prevent it becoming blocked & placed in a small (~120ml capacity) bottle which in turn was secured close to the cowl exit, with a loose fitting cover to exclude any direct ram effect, no change with that either. The hope was that by placing this container as close as possible to the cowl exit & without being in the direct slipstream that would reduce the "cowl pressure" effect as much as possible. The Sling factory technical response has been that ALL of their 912ULS installations are the same as my original configuration, some display the low fuel pressure problem & others don't. They have not found a reason for the intermittency of the issue or a successful remedy for those aircraft affected. Any additional ideas would be warmly welcomed by me!

Re the carb piston slides, yes, I think something has gone astray with the re-installation either as you suggest or debris or both. We were aware of the issues you highlight & I had watched the video prior to the SB being performed, I was certain the diaphragms were correctly installed but I think now the first course of action is to dis-assemble, clean & CAREFULLY re-assemble.

Many thanks.

A brief update, I flew the aircraft this morning, checked both choke levers are definitely on the stops when choke off. Pre start I checked the operation of the aux pump, watched fuel flow & pressure rise then switched it off before flow decreased much. First start attempt without choke it didn't fire which is quite normal for this engine on a cold start. Second start attempt using choke was normal, it started before the second prop blade went past the windscreen and was smooth - back to normal for this engine so it does seem there is something causing the engine to flood when using the aux pump prior to start.

Many thanks to those who have contributed to this issue.