New Kitfox owner

[av8rps]

My rotax friend came by this morning (snip, snip)

The second problem arose when we did my first full power run up. Engine runs great at or below current ambient pressure (about 22 in/hg) but does not want to go above that and surges when I try. I think this may be due to leaky carb bowls. When the 3 way solenoid pressurizes the carbs the bowls leak and can't supply enough fuel to the motor. ?? I was planning on rebuilding the carbs but I have found new/unused 914 carbs on eBay that I am considering buying. It seems like a good deal but depending on there age from manufacture they still my need new gaskets. But for $350 for the pair it may be worth the gamble. Any previous experience/advice is welcome. Just keeping you guys up to date.

A 914 powered Highlander crashed once (I was there) with a very similar problem of "surging" during high throttle application and warm temps. The best we could tell after the crash (which was very severe both to the pilot and the aircraft) was that because the 914 gets all of its fuel from two electric pumps that continuously run fuel from the header tank to the engine , with all unused fuel going back to the header tank, that the fuel was getting hotter and hotter the more it was run on the ground, which caused fuel vaporization resulting in surging and eventually significant power loss right after takeoff. Lesson learned that day, run all unused fuel back to the wing tanks where there is a larger quantity of cooler fuel to mix with the hot fuel coming back from that engine compartment. Plus the air going over the wing also will help to cool the fuel, wheras the small header tank just lets the fuel get hotter the longer you run the engine.

I don't know for sure if that is why yours is surging, but the scenario sure sounds a lot like that Highlander. I'm guessing if it wasn't summer and if you weren't running it hard on the ground that maybe you wouldn't even know this was an issue. But now that you know that could be a possibility you might want to check out how yours is plumbed. The Highlanders were modified to return fuel to the wing tanks and many 914 Just Aircraft have since been operating successfully.

Knowledge is power...

[DesertFox4]

Thanks Paul. Good info.
I have very little time in 914 powered Kitfoxs. Maybe 4 hours combined. One here in Phoenix years ago and the rest Stick & Rudders S-LSA's.
No surging in any of those that I know of.
Got a friend building one here in Phoenix and we'll pass this on in case he misses it here in this thread.

[Av8r3400]

How big is a highlander header tank compared to a Kitfox tank?

I thought theirs was a very small one, a piece of wing spar tube, like an Avid. I would think the larger Kitfox tank at a couple of gallons would be able to disperse enough heat...?

[Esser]

Kitfox headers are one gallon and believe it or not I think the highlander is 1.5. When I was looking at the UL, they recommended I increased my header to 3 gallons minimum or return to one of the wing tanks. This was due to vapour concerns. Hope this helps.

[inflight]

Taxied for about 20 mins today! Good news is that I don't seem to be getting any more oil past the turbo into the airbox. Best guess is that I had residual oil that accumulated over that 10 year sitting period and that once blown out and the motor run regularly it won't be a problem.

I still couldn't take the MAP past ambient air pressure and I don't think it is a fuel vaporization issue as it is a problem from the get go, not after running for a while. The previous owner flew for about 150 hours with the return line T'd right back to the fuel pumps on the engine side of the firewall. I don't like the setup of the fuel system and plan on changing it, but I haven't decided what I want to do yet.

Does anyone know what the factory is doing with the SLSA? I may need to take another trip to ID just to check out the airplane closer. At the time I did my training I didn't know enough about what I was looking at.

I think fixing my leaky carbs will make a big difference in my surging issue as right now anytime I go over ambient pressure I get fuel seeping from the fuel bowl.

Thanks to Paul for the heads up. I was aware of the vaporization issue but still am not sure how I want to proceed. How would one run the line back to a wing tank? Would I need to tap a new fitting in? Obviously the header tank would be way easier.

[scottr]

Congratulations Mark, watching your first engine start was pretty exciting. I am slow building a Kitfox and watching the videos has gotten me more motivated to work on it again. Good luck and have a great time with it, it's going to be a great adventure.

[Danzer1]

As this relates to the other unanswered question on the bleeding brakes thread about air bubbles in a fuel filter - and I swore off communicating further on that thread. I'll post my food for thought here:

Guess what that vapor lock is? Just like a giant AIR LOCK (BUBBLE) partially or completely blocking the fuel flow! And a fuel pump puts out a lot more pressure than a brake return spring!

I'll let you guys chew on that one for a while!

Greg

[inflight]

Congratulations Mark, watching your first engine start was pretty exciting...

Thanks Scott! There will be more to come. Anytime you are up in the mountains let me know and come on by! Honestly, this seems like it is taking so long, I have a new respect for you builders.

[Ramos]

Mark, I have been contemplating giving Stick & Rudder a fairly serious chunk of cash myself. Any thoughts based on your experience with them would be much appreciated. Feel free to post, PM or email me direct. Thank you.
Jon
jonr@mcgg(dot)net

[inflight]

Jon-

I have nothing but good things to say about Stick and Rudder. I had an excellent time and learned a tone while at it. Paul was very accommodating in helping me make it a dream trip. I stayed at Garden Valley in my truck camper as I prefer camping to hotels and Preston flew there and picked me up in the morning and dropped me off after the lesson. There was an extra cost involved to do that but it was offset by not needing a hotel or transportation. I would go for it, you won't regret it.

-Mark