Kitfox 4 + HKS, the saga continues

[Geowitz]

Sounds like you're making definite progress and it makes sense - Just giving you a hard time , but as we said before, the opposed 2 cylinder motors are extremely picky about carb balance/sync and if one is missing parts that would definitely make that impossible. Glad to hear you're getting closer.

[Av8r_Sed]

It looks to me that your missing carb part is a needle jet. That would certainly explain the poor running with increasing throttle.

You can find exploded parts diagrams for the Bing carbs on most Rotax supplier's websites.

[Timberwolf]

Good to see you're getting things worked out. However, I would have a huge bone to pick with the A&P and would be going over his head. It may be someone else's life you save. Really can't believe he would leave a part out of a carb. Just seems like careless workmanship. Attention to detail isn't a plus with an A&P, it's a necessity.

[napierm]

Wow. Yeah, that is the advantage of learning how to do the work yourself. You know how it was done -> right.

Good luck,

Mark

[rwaltman]

Carb kit arrived - Not as pretty as akarmy's tailwheel, but will keep me equally busy for a while. Will be working on the engine over the weekend.
Ah, the thingie was indeed a 2.70 needle jet.

Roberto.

[rwaltman]

I would recommend tearing down / cleaning the carbs thoroughly.

Prophetic words ...

Problem solved! (After a day long dance practicing the 2-forward,3-backward step.)

Remove both carburetors, disassemble, check, there is a little dirt in the bottom of one of the fuel bowls, practically nothing in the other. Clean it. (Why only one?)
Remove almost everything than can be unscrewed (but not the main shaft.)
Clean everything (bodies and small parts) with a carb-cleaning spray can, rinse with lukewarm water, blow dry with compressed air.
Most things look OK, (engine has only 80 hours,) so we decide (Rotax-guy-that-knows is with me again, as Guy-that-knows-Bing-carbs,) to reassemble without replacing the O-rings and gaskets.
Carbs are put back together, making sure the missing needle jet goes where it belongs.
Install in airplane, hook up everything, fire the engine, and it runs exactly as badly as before.

Scratch heads, discus other possibilities. Check ignition. I saved the previous set of plugs, and with 80 hours they look cleaner than the new ones with a few hours under 100LL. Replace plugs, no change.

Check and re-check all connections to both carbs, specially the "bad" one, (the one that was missing the jet, the one where the EGT decreases after some point.)
Run the engine a few more times. At some point Rotax-guy pulls by hand the throttle in the "bad" carb. Engine speeds up as it should. Pull the throttle in the "good" carb, engine speeds up a little, and then coughs, EGT goes down etc.
Either the EGT senders are cross-wired or I cross-read the EGT's gauges. Which one is the right one? The one with the scale to the right, or the one with the needle axis to the right?

So, the suspect is now the other side of the engine. We just cleaned the carb, could there be a problem with the left cylinder or valves? We swap the carbs, the problem moves with the carb to the other side. Good, no top-end engine problems.

Newly-bad carb is removed, disassembled again, inspected more carefully. The main jet is blocked by an orange, crystalline like substance that survived previous spraying and blowing. (And my poor inspection.) This time all parts go into the heavy-duty carb cleaning stuff, the one that you soak the parts in.

...Fast forward to engine run-ups...

No problems at all starting or speeding-up. Went several times to 4500 RPM, briefly to 5000.
Held 4500 (78% of max continuous RPM) a couple times for more than 3 minutes without a hiccup and with the EGT's identical at 1200. The vibration at RPMs below 2000 is still there, but at acceptable levels. There is some lack of balance, of course, after touching the control cables so many times. I'll take care of re-balancing the carbs tomorrow, as well as doing run-ups at full power and re-pitching the prop for the correct static RPM.

( I believe now that I got the airplane already without that needle jet. Apparently it missing has a relatively small impact on the engine, at least at low altitudes.)

All this not for free... (a) One of the choke springs went missing in action. I never needed to use the choke to start the engine, so we safety-wired it in the closed position until I get a new one.
(b) I left the scene for a few minutes, and in that time another airplane came back to its hangar, with the Kitfox partially blocking the way. Guy-that-knows-Bing-carbs does not know Kitfoxes, at least not the wing folding bit. He pulled the pin and begun folding one wing without disconnecting the flaperon first. So now I have slightly bent flaperon control horn and push-pull tube to fix.

Roberto.

PS: Spell checker insists that "flaperon" should be "chaperon"

[Esser]

Guy-that-knows-Bing-carbs does not know Kitfoxes, at least not the wing folding bit. He pulled the pin and begun folding one wing without disconnecting the flaperon first. So now I have slightly bent flaperon control horn and push-pull tube to fix.

Man you just cant get a break.

[rwaltman]

Well, it is beginning to look as if I do have an airplane after all.
Run 1.5 hours on the Hobbs today. Some 20 minutes taxiing, re-setting the carbs idle balance, checking the gauges for normal readings.
For the rest, took the plane to the end of the road, tied the tail to my car, and run more than one hour non-stop, going from idle to full power and back. Spent 15 minutes at full power, (in slices of 2 to 3 minutes) Temps, pressures and EGTs were OK. Carbmate readings at highest sensibility:

0 2000 RPM (Idle)
-1 2500 RPM
0 3000 RPM
+1 3500 RPM (Some shaking)
+1 4000 RPM (Some shaking)
0 4500 RPM
0 5000 RPM
0 5500 RPM
0 5600 RPM (WOT)

Cannot do better than that. Did a shorter run after removing the Carbmate and connecting back the vacuum balance tube. Was expecting some improvement in the vibration, but if there was one, was not noticeable. Guess that helps only when the carbs are out of balance.
The last 1/2 inch or so of throttle travel does not increase RPM, was expecting a smaller "dead zone"
The 5600 RPM full static is a tad high, did not have the time today to re-pitch and try again.
Will do the same run tomorrow, but with the cowlings mounted.

I still see a few weekends of work taking care of small things, but things are definitely looking good.
Thanks everybody for your help, advice and support. (And no, I am not done bugging you guys yet.)

Roberto.

[Dorsal]

Roberto,
Glad things are looking up, you will certainly know your plane when you fly it.

[rwaltman]

Another day, another 1.5 on the Hobbs. As before, that includes a continuous run of more than one hour with my car as anchor. The rest taxiing around.
Before starting, I added 1 degree to whatever pitch the prop had.

The good - That brought down the static RPM from 5600 to ~5250, which is about right. Not a hiccup during the hour long run.

The bad - the badvrations are back. I suspect the reason is that I removed the leading edge protection tapes, (one was damaged and needed to be replaced) and that may have thrown the prop out of balance. So, add to todo list - 1st, statically balance prop. 2nd, dynamically balance prop. (Is there a Dorsal in the room?)

The ugly - a new problem is that with the new propeller pitch and the need to keep RPM above 2000, (to avoid really really bad vibrations,) the Kitfox really wants to move and to move fast, too fast for my current skill level.
Taxing became an exercise in controlled braking. Need to find a way to bring down the MSR. (Minimal Smooth RPMs) In addition to the prop balancing I still need to retorque the engine mounts, per Mnflyer's suggestions. If that doesn't help, I may switch to a two blade prop even if that means a performance hit.

Yesterday's run was done using only the electric fuel pump. (Had the Mikuni disconnected to use the Carbmate.) Today the Mikuni was back on the job and the electric was not used. So both pumps are OK.

This time I brought my headset - Radio works, intercom works, (at least the pilot's side,) PTT button on the stick works. Microphone, not good enough. KMGJ has an automated transmit check. With the engine on I could not understand my own voice. Need to experiment with microphone shrouds/covers. Any suggestions?

One CHT doesn't work. Seat cover tends to slide forward. Removed cargo bag and liners, (want to keep it that way.) Need some cover on the cargo area so things don't fall in and go to the tail. Need to make sure the missing liners do not expose wires or hoses that could get entangled with my shoes. Fuel consumption from both tanks is far from even. Rudder cable tension spring keeps falling off. Flaperon push/pull rod still bent. And the engine vibrations. I think that's the complete squawk list. For a machine that did not run for 2 and 1/2 years could be much worse.

Roberto.