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cardinal flier
10-17-2010, 10:56 AM
My new, unflown Model 4, Rotax 912S, Ivo 3 blade, IFA ultralite, has developed a problem. Vibration causes the carburator floats to vibrate and unseat the float needle, causing the engine to run rougher, and then more vibration. The local Rotax dealer said that an unbalanced prop or loose motor mount will cause the right carb to vibrate. Everything is tight and the prop is new. I've tried everything, adjusting and syncing carbs, etc. I thought I had the problem fixed, but when I started the engine this morning for a final check, fuel flowed out BOTH carb vent lines because of BOTH carbs vibrating. Any and all thoughts are appreciated. I'm including my cell phone in case anyone wants to discuss this further by phone. I'm on the West Coast so plan accordingly, please.
Bruce Estes
(650)504-4464

Av8r3400
10-17-2010, 05:56 PM
Check for cracking in the rubber boots between the intake manifolds and carburetor bodies.

Additionally, isn't the Medium IVO the recommended prop for a 912ULS due to the extreme start and shut down violence? I believe cracking of the smaller blades of the ultralight prop were resulting in that installation.

jtpitkin06
10-17-2010, 10:39 PM
This is a tough one to diagnose on line. But we can try to do some eliminating before I ask my local prop balancing guru to jump in.

First item: Is this the correct prop? You say it’s a light IVO, I think Larry’s posting is correct. A medium weight prop is recommended. If so, all bets are off.

However, if it is the correct prop then we may proceed. OK… the prop is new.
Was there a certificate that came with the prop saying that it was within spec and balanced before being shipped?
Did anyone check the balance or weigh the blades before installing the prop?
Is this prop equipped with a spinner?
Is the spinner balanced?
Is the crush plate balanced?
Does the spinner wobble?
Did anyone put a dial indicator on the spinner back plate to check run out?
Did anyone paint the prop on either the front or the back?
Is there paint on the prop tips?
Are the prop blades set at the same angle?
Are the blades tracking in the same plane, under 0.050 inch?

Let’s start with these and see if we can figure this out. If we don’t find something here that is obvious, then we will move on to the engine.



John Pitkin
Greenville, TX

DesertFox4
10-18-2010, 06:09 AM
Bruce thinks he's solved the problem from info. I received yesterday. Looked at this time to be a carb. setting problem. One of our members called him directly. He will jump back on if it turns out to be something else. Also I was told that only the mechanical sync.
Also it's important to make sure the "chokes" are returning to full off position after engine start. Lots of things to check on a newly installed engine.

I've used a method for shut down for years as do most I fly with that eliminates the abrupt stop you get on the 100 hp. due to it's higher compressions.

Shut down: throttle to 2,000 rpms, as ignitions are turned off retard throttle smoothly to full idle. Practice makes this perfect but my prop. blades come to a nice smooth stop every time. Much easier on the gearbox.

cardinal flier
10-18-2010, 04:55 PM
It appears that I've solved the problem. When all else fails, go back to the basics. I started over with the carb mixture and idle speed adjustments and have now successfully run the engine twice. I think that the Rotax likes to have the mixture a little rich when cold, and I was leaning the idle mixture too much, when the engine was hot. The hot engine would tolerate the leaner idle mixture., but only when hot. I will run the engine a couple of more times on the ground, cold and hot, and then my Kitfox is ready for first flight. Thanks for all of the help.
Bruce Estes
KF IV, Rotax 912S, Ivo IFA, Dynon D180, etc.

jtpitkin06
10-18-2010, 07:08 PM
Did anyone look into the lightweight prop issue?

JP

cardinal flier
10-19-2010, 08:05 AM
The lightweight prop is not an issue. There are MANY Kitfox owners with Rotax 912S with the lightweight prop. A buddy of mine has over 1500 hours on his lightweight prop with no issues. I spoke with MANY owners about the comparisons between the medium and the lightweight, and was told that the medium might give me a little more cruise speed at certain altitudes, but the lightweight will give me a quicker climb rate, along with generally more sprightly performance.
Bruce

jtpitkin06
10-19-2010, 02:15 PM
Great! Sounds like you have everything in order. Hope to hear of your first flight experience, soon.

JP

cardinal flier
10-21-2010, 04:31 PM
Well, I thought I had the problem solved. I've started the engine several times to make sure that it ran correctly, and until yesterday, I had no problems. Yesterday, after starting the engine, and shutting down after running rough and dripping gas out of one of the carbs, I discovered that one of the choke levers had not returned all the way to the off position. Rotax confirmed that the choke (enriching) levers have to return to the stops or the engine will flood on that carb. My levers, occasionally, would return to about 95% of the return travel, but not 100%. So, today I changed the geometry of the return springs, changed the geometry of one of the choke cables, and tightened the springs. On a subsequent cold start, using the chokes, the engine ran perfect. More testing (starting the engine cold) to be done prior to first flight. Hopefully, next weekend will be first flight.
Bruce

DanB
10-21-2010, 05:43 PM
Bruce,
It sounds like you had to go through the fire b-4 you can fly...maybe we can nickname you The Phoenix. :) Probably not at all unlike what many others have learned the hard way. These kind of posts are helpful to many of us who are right behind you, so we tip our hats for the information. Glad to hear your first flight will be soon.

John, your answers are always refreshing to read and I learned some good info on props! I have a spinner to install, but had given no thought to getting it balanced. It's the little things that can get you I guess.

Copperstate is underway and I will probably make it out there tomorrow. Steve Kellander is out there today probably swapping hanger tales with the McBeans. Hopefully photos to follow in the next couple days.
Tailwinds!

cardinal flier
10-23-2010, 03:13 PM
Unbelievable!. I started my Kitfox this morning for another cold start engine test and the engine proceeded to run rough and spew fuel out the carb vent tubes, like it has done before. It ran great the last day on several cold starts. So, back to the drawing board. It is NOT the chokes. I have another strong suspicion, and have made more changes, but prior to going public with it, I'd like to know how many Kitfox owners are running auto gas with ethanol thru their "ethanol proof" fiberglass tanks. Thanks, Bruce Estes

Dorsal
10-23-2010, 03:41 PM
Check the thread "help I soiled my carburetor" not sure it is related but possible

cardinal flier
10-23-2010, 07:48 PM
Dorsal: YOU'VE IDENTIFIED MY PROBLEM. YAHOO. I owe you a beer or more. The "brown stickey stuff" is the key. Yes, I've got it. Today, I sloshed the tanks with avgas and ran the engine on avgas to flush. Then I drained everything out of the wing tanks and left the caps off to dry out. I'll check tomorrow. Where can I get decalin?
Bruce Estes (in impatiently waiting for first flight mode)

Dorsal
10-24-2010, 04:40 AM
So sorry to hear you have BSS (brown sticky stuff) :( what a PITA. I get my Decalin from John&Deb, if the tanks are still sticky today you may want to rinse with something stronger (I used acetone). I would also recommend checking the carbs for BSS, if present disassemble and clean with carb cleaner.
Take the time, the first flight is more fun when the engine stays running.

cardinal flier
10-25-2010, 06:49 PM
This afternoon, I cleaned both carbs. The BSS (brown sticky s**t) looked like pancake syrup and was everywhere from the carb inlet, throttle butterfly, carb venturi, needles, etc. What a mess. These carbs are pretty simple and using Gumout and a compressor to cleanse, cleaning them was not a problem. I ran the engine off of the header tank on Av-gas and it ran perfect. Tomorrow I slosh the tanks, adjust the carbs (sync, idle speed, and mixture) and then keep testing for a couple of days. Again, if you have not run auto fuel thru your tanks, don't be a test bed. Use ave-gas and save yourself a lot of frustration and problems. First flight coming next week. Bruce