model 7 fuel bulkhead fittings

[mcomeaux53]

Recently purchased model 7 with 912s with aluminum air box.
Problem figuring out fuel lines . I understand the 5/8 going to the pump
From the firewall fitting. No problem so far but now from the output port
To hose that tees of to carbs and another arraignment from there to another
Fitting in firewall. Venting system of some sort? Haven't removed console
Yet. Any ideas? Mike

[Floog]

The line coming off the 'T' between the carbs is a fuel return line that goes back through the firewall to the header tank. There should be a check valve in the line as well. You purchased a fun machine!

[mcomeaux53]

No valve on hoses. I was considering plug off fitting. Any problem with that move.

[Floog]

The Andair check valve is usually located behind the firewall and near the header tank in the return line. Search 'fuel return line' in this forum for a discussion. The purpose is to prevent excessive pressure/vapors in the fuel lines. It's recommended by ROTAX. If it's already there, why remove it?

[Dave S]

Mike,

I have an earlier series 7 (kit from prior to John owning the company). The construction manual for the fuel system did not include the fuel bleed/return line at that time. I believe the return line was later recommended by Rotax and it is included in the newer kits.

My experience without the bleed line is an occasional hot start problem if my timing is not right after shutting down. I haven't suffered any more than the very occasional embarrasment trying to get the darn thing started gracefully on a hot day witrh bad timing so I have not done anything about it. There are a lot of Rotax powered airplanes without the bleed from days previous.

If you want to plug it - you have lots of company anyway.

If you have the plumbing I would certainly keep it. Use the check valve if you keep the system so you don't get crap bypassing the filter.

On the airbox - if you already have it - I'd keep that too -- it does a few things. 1) According to Rotax, without it you get a 5% horsepower deduction - it's an engineered part of the induction system. 2) It securely holds the carbs in place if the rubber flange deteriorates. 3) gives you an option for either alternate air or carb heat.

Sincerely,

Dave S.

KF7 Trigear
912ULS Warp Drive

[jiott]

Definitely keep it and install it correctly. The Rotax installation manual tells how. It nearly eliminates vapor lock problems on hot starts.

[kmach]

Can you post some pictures ?

[mcomeaux53]

Found valve I and installed lines as prescribed
Thanks for all the response......