Low Fuel Pressure

[Dave S]

Don,

Precisely! Your take provides the exact explanation and reason why Rotax makes this recommendation. So often, manufacturer's instructions say what to do, or what they recommend, but not the details of why.

Your logic is spot on.

There are a few (very few) of the older carbureted automobiles that had designed in three spigots on the in line fuel filter. One in, one out and one return via a bleed on the other side of the fuel pump.

Appreciate you sharing what you discovered on the plane. I can see a return line in my future too - having suffered the same occasional hot soak situation with a flooded start on a summer day. ( FWIW - won't happen when the outside air temp is 5 degrees F).

Dave S

[Dave Holl]

I thought the reason for the return fuel line was to reduce the chances of fuel vaporization?
I guess it also stops fuel pressure build up with heat when the engine is stopped!

[Dave S]

Dave H,

Sorta both or either - in a hot soak soak shutdown - the bleed line relieves the pressure between the pump and carb so flooding does not occur via the carb needle valve - what starts out as warm fuel can certainly progress to fuel vapor if there is enough heat buildup. It's a matter of degree.

In any case - without a bleed line excess fuel or vapor or both can be dumped to the carb past the float valve and cause flooding - the pressure buildup will be released through the float valve because it can't go the other way.

Sincerely,

Dave S

[Dave Holl]

Should a non return valve be fitted in tis line at the firewall?
Dave

[Dave S]

Dave H

In my opinion, a person should follow the recommendations of Rotax for the specific engine regarding how to hook this up. If you happen to have the engine installation manual; or search their site - you should be able out find what their recommendation is.

Sincerely,

DS

[kitfox2009]

Hello All
Yesterday I installed my new fuel return line. I obtained the "pilot jet" from Rotax. This is a threaded jet designed to fit in the Rotax fuel distribution block. Probably a similar unit could be obtained from a motorcycle shop. Anyway, with a slight modification I installed it in the fitting going into the top of the gascolator. The fuel pressure stays at 5 PSI through all power settings and drops to zero within seconds after shutdown. I have not had the opportunity to test it for hot starts yet but hopefully this will eliminate the problem.
Cheers
Don

[Dave S]

Don,

Thanks so much for posting your results so far. Will certainly be interested in how the hot starts work out. Sounds like your fuel pressure is right where it should be now.

Do you happen to have any photos you could post which show the completed installation layout including the gascolator hookup?

I have been mulling this over in my mind for a while but haven't taken the step to do it yet - but do want to to. I have the occasional hot start deal going on too; and, I don't have a gascolator (another likely improvement).

Sincerely,

Dave S