Carb overflow lines

[Dick B in KY]

For those using the Rotax 912ULS without the factory air intake. Where do/have you run your overflow lines from the float bowls to prevent fuel from dripping on the exhaust, and do you have some kind of shield to prevent heat from cooking the bottom of the carbs??

Thanks,
Dick B (building SS)

[wildirishtime]

I decided long ago I never liked that design - some guys have those shields that 'catch' the fuel but with the airflow i'm not sure how well
that will work.

What I did that I have tested (when the carbs are out of sync is a great time to overflow your carbs!) and worked great was to run a line from the carbs towards the firewall about 4-5 inches (not much more than that!), and put a tee in pointing UP with a few inches going UP on the firewall. This gives you an air vent pipe with adequate height to prevent spillage for EACH carb.... take each of those tees down to exit underneath the aircraft. I later tee them together and insert a metal overboard tube with vent holes cut in that metal to prevent syphoning effect or backpressure inside my carbs. Lets see if I can draw this:



| |
| |
|---CARB CARB---|
| |
-------------------------
|
|
|
metal tube
|
|

You get the idea.... it's worked great. Don't try and use just one airvent, I found that it just won't FLOW downhill like you need it to and a fuel-filled carb overflow tube is no good because that needs to normalize with atmospheric pressure as best I understand for proper mixture.

Someone will likely jump all over me here but this system works excellent and produces minimal risk if you ask me compared to dumping fuel UKNOWINGLY all over your hot exhaust....

~Wild

[HighWing]

Not a ULS, but same issue. This is what I did.
Lowell

[kitfox2009]

On a suggestion from Roger Lee, I replaced these tubes with longer ones and routed them to the back of my air filters. I drilled a snug fit hole in the flat end of the filter and plugged in the tubes. Been that way now for about 80 hours and seems to work just fine. If there ever was a spill it would just get sucked back into the carb.
To prevent excessive transfer to the carb bowls after shut down I attached two pieces of "starter heat shield for racing cars" between the rear cylinders (just over the exhaust) and under the carb bowls. These are held in place with zap ties and are easy to remove for carb servicing. The material is a very flexible/woven reflective cloth. They worked very well this past summer in 30+C temps. No more "hot start" issues.
Seems to work for me. Welcome comments and/or suggestions!
Cheers
Don KF5 Vixen 912UL IVO IFA.