It's confirmed I'm a Fox-aholic

[Norm]

4.8 Hrs on the Fox today. Flew to the Red Deer River for the badland tour. It's a 50mile flight from homebase. From there back to Linden for cinamon buns and coffee, back to a friends farm and then off to Red Deer. I picked up an old friend that taught me to fly remote control airplanes some 30years ago. He is now 80 and smiled all the way around the area. It was good to make an old mentor smile.
I switched from three blades on the 912 UL to two blades and picked up 10mph. It seems to cruise at 90-95mph at 5200 RPM. With the three blade it sees about 80-85mph. I did get a noticable vibration with the two blade and went back to the three blade to retest when I got back to homebase. Same result, back to 80-85 with less vibration but still some. So one of two things I am thinking. Carb cleaning and balance again or the gearbox needs servicing. I have previously balanced the carbs and had it fairly smooth but it is possible that some dirt has gummed the carbs in the 16hrs I now have on the plane and a cleaning and rebalance is in order.
I know some have had gearbox issues and it seems to mimic carbs that are out of sync. This is an older UL I think it is probably due for service. It is tough to turn over and almost has a metal scraping sound as you turn it over.
Any thoughts on carb sync or gearbox service might be helpful.
Norm

[Danzer1]

Not a lot to go on here Norm, could be lots of things.

How old is the engine - years?
Hours?
Did you get a log book with it?
Serviced regularly?
When was last carb balance performed?
Has the engine ever been torn down and inspected? How long ago - hours?
Has the gearbox ever been inspected? How long ago - hours?

Is this the same 2 blade prop you had severe vibration with on your other aircraft?

What are the props you are referring to now?

Have either prop/engine/gearbox combinations been dynamically balanced?

Greg

[Norm]

Not a lot to go on here Norm, could be lots of things.

Greg

Your right Greg not a lot to go on. The motor was a used motor that I was lucky enough to pick up out of the Spokane area. It is a very early model with the aluminum box ignition. It had a helicoil for the head bolt go and it would not keep torque. Thanks to Hal at Zipper with his explanation I was able to replace the helicoil with a threaded insert. I only pulled the one cylinder and was amazed at the condition of the engine. I did not tear off the other cylinders as I tend to live by the “if it aint broke rule”. The motor runs very well but I was experiencing some roughness in the 3000-3500 range on descent. I have a ton of experience with the 582 but the 912 is a new beast for me. I am unsure of the total hrs on the motor but think it is in the 800 to 900 range. I do not know when the gearbox was last serviced so that became an area of suspect.
I talked to my Rotax authorized tech last night and he gave me a couple of things to check on the gearbox. (Magnetic plug, friction test) He does not suspect the gearbox and thinks I should focus on the carbs first.
I plan to clean the carbs using starting fluid and compressed air as others have pointed to on this forum. Then I will resync and check things from there.
The propeller is an IVO 72inch ultralight and while it is smoother in the three blade configuration I do get about 10mph more with the two blade configuration. This is still in the early testing stages for best performance and I have the in-flight adjustable hub that I will be going to eventually. I am thinking that the two blade will be easier on the electric motor when I go to the In-flight Adjustable.
I know it could be a ton of other stuff including ignition but thought if someone had similar experiences I would be happy to listen. Of course that could be a problem as well as I could end up chasing the wrong problem.
I will start with the carbs and go from there. I'll let you know how I make out.

[Slyfox]

I have only one thing to put out about the prop. when I had my 912ul on my fox I had the untralight Ivo also, but it was 68". you can cut the ends off, just make them all the same amount. start by going to 70" and try it. seems when my ul was running right I was around 98kts. much faster then what you are seeing. mine was also inflight adjustable. I kept it at 5200rpm. I think if you take 1/2 inch off each blade will make for 1 inch total. best to make sure of that though.

generally the rotax will be a little bit rough when around 3000 rpm when coming into land. but if it's a little too much the middle jet is the culprit in the carbs. I take the bowl off and take the jet out, spray some carb cleaner, even brake cleaner works fine up from the bottom, should see fluid come out a little vent that's right at the opening of the carb where the filter goes on. once that happens shoot some air in there and put it back together. hope this helps.

[Norm]

Thanks Steve that is helpful info. I went to the hanger, took the carbs off and took them home with me. I am going to do a complete clean. I think I saw you or someone post about spraying cleaner into the jet and getting great results. I remember doing that to a 582 carb and got the best running 582 ever.
Just curious and it will not affect my running the UL but what kind of perfomance improvment have you seen with the ULS.
Thanks again for the tips.

[Norm]

My Savage cub buddy just sent me a link to this video.
https://youtu.be/_AbuCySdVio

Landing at his farm. Still some work to do on landings but if I try real hard, occasionally I get a good one.

[Slyfox]

I wouldn't go back. I do a constant 103kts wide open, I just set the rpms to 5200, you can do this with yours if you have inflight adjustable. take off is very cool. I keep the rpm's @ the top of the yellow, I think that is like 5800. once I level out I set for 5200. keep the throttle all the way in. I spin a medium prop, IVO. burn more fuel, but who cares.:D

[Slyfox]

one more thing. If I want to go low and slower. I back off to 4200rpm with the throttle, then I reset the prop to 5200. I also use this setting when going in to land. makes everything set up also for take off. also it gives me a good engine braking by pulling off the throttle all the way. At this setting I generally go about 84 Knotts. a nice setting for running low. don't ask how low, I won't say. like one guy said, always say 500ft :rolleyes:

I did talk to the boys from Rotax at OSH and they said the more you run at 5200 the longer your gear box will last. so I don't go under that unless I'm landing, or taking off for that matter.

[Slyfox]

that vent hole I mentioned in the carb for the mid range is real tiny. gets plugged a lot. I generally clean that when I do an oil change, just takes a few minutes. generally runs better after I do it.

[Norm]

So I did a clean on the Bing carbs for the 912 and found two issues.
Short Video
https://youtu.be/bo_mgNlryII

[Slyfox]

yup that would do it.

[jrevens]

So I did a clean on the Bing carbs for the 912 and found two issues.
Short Video
https://youtu.be/bo_mgNlryII

That was interesting, and could be very helpful for some of us... thank you, Norm!

[Norm]

I guess based on what I found, paper towels are not a great thing to use when cleaning a carb.


That was interesting, and could be very helpful for some of us... thank you, Norm!


John this forum is and has been such a great help I am happy to be able to pass on something that may help others and contribute back.

[Slyfox]

only compressed air, good find

[Norm]

I think the enrichner problem was more the culprit than the paper towel. The paper was stuck between the needle jet and the holder, and while it might affect mixture it would not change dramaticly from one run to the next. The enricher could stick and give a total different run from one start to the next. My thoughts Proof will be in the run tomorrow (depending on weather).

[Av8r3400]

Yep. Enricheners can be an often overlooked problem.

Did you disassemble any further than that? Did you weigh your floats?

[Norm]

Yes cleaned everything including main jets, low speed jets, mid range, enrichener circuits, but to be honest did not weigh the floats or remove the float needle. I also removed the diaphrams and inspected. As you said they were keyed and easy to put back in the same order. i am excited to see the results I will install tomorrow, balance and let you know if there is an improvement.

[Slyfox]

all you need to do with the floats is look at them when you remove the bowl. if you are careful you can SEE how the float works, if it sinks, it's bad. that's how I found a bad one a few years ago on my ul motor.

[Norm]

all you need to do with the floats is look at them when you remove the bowl. if you are careful you can SEE how the float works, if it sinks, it's bad. that's how I found a bad one a few years ago on my ul motor.

They were good when I removed the bowls with the fuel in them. I did not want to remove the float needle as I have done that before and was never sure I did not bend the level out of spec. I will try this first.

[Norm]

I put an hour on the Fox today after cleaning the carbs and I am happy to report it is much better. Not perfect as there is a high frequency buzz type of vibration but it is much better. I will continue to work on it and see if I can get it perfect.
Norm

[Av8r3400]

Excellent, Norm!!

[68niou1]

Norm-

I just went through the same thing as you- it's amazing how weird these Rotax's will run with iffy carbs. The worst part about it is there is nothing that exotic about the darn things, but if they are not just right it will give you all sorts of grief. One major thing to check that no one ever thinks about(including me until recently) is the slides. With age those things get sticky and wear, and they will cause all sorts of weirdness(rough running, vibration, even complete engine stop) so check the slides and the inside of the carb- if you see any wear or marks that is bad. Also push the slides up and make sure the return is smooth- on mine they would stick one out of 10 times so it's not very obvious. FWIW

Scott