912 Big Bore

[KitfoxJ]

That's GREAT news. Keep us posted.
Jay

[WWhunter]

Haven't been able to fly/work on my plane since last fall. Just returned to MN a couple weeks ago and as I posted in a different thread, I had voltage regulator/rectifier issues last fall also.
Robbed the Ducatti unit out of the KF IV I purchased last fall and started the engine. Replacement rectifier 'might' have been the problem as it did appear to be charging but I didn't run the engine long since it was running terribly.

Had this problem just before leaving for the winter...extremely rough running engine. Both carbs were rebuilt at the same time as the Zipper kit was installed.

My question: is there a need to change any of the jets/jetting with this increase in bore? I would think it might need it. Upon checking things over the plugs were quite black, ie, running rich. Hate to say this, but this 912 has given me more problems than any motor I have ever rebuilt.

[Av8r3400]

Keith, where did you get the carbs rebuilt? These are not complex carbs, but I have seen rebuilds from Rotax service facilities not work right without re-rebuilding them…

I had to disassemble and reassemble my carbs several times in order for them to run well.



But first a few simple questions:

1. What notch do you have the main needle clips in?
2. Does it run rough at all? If so, at what RPM?
3. Did you replace any of the "soft" components? Carb Boots, diaphrams, floats, etc.

You may have gotten some of the "bad" floats… ?

[WWhunter]

I rebuilt them myself. Stupid? I dunno, but to me they are pretty basic. I purchased the complete rebuild kits from LEAF while at Oshkosh (2013) but didn't get around to building them until I put on the cylinder kit. The kit had new floats, gaskets, diaphrams, etc. I pulled the float bowl off from the side that seemed to be running the richest. I wanted to see if the floats had sunk. They didn't appear to be bad.

I did notice when it was running (albiet rough) that the vent tube on this side was spewing fuel. Hence the reason for checking the floats. The fuel might just be from the excessively rough running engine.

In doing some research on here I did see mention of 'NOT' oiling the K&N filters. I am wondering if this may be contributing to the rich fuel mixture. Something I really hadn't thought of other than I cleaned and reoiled them beforehand thinking they might be dirty and causing the problem.

I have had these carbs apart several times trying to figure out why I am having such a rough running engine. It may be an ignition module issue but I highly doubt it since I can get it to run very smooth at some RPM's but above or below that RPM it gets rough. I use a Carb-Mate for syncing.

I will have to check on which slot I have the clip on. I honestly forgot.

[Av8r3400]

They are simple. Rebuilding them yourself is usually best. You get a better understanding of their operation and assembly.

K&N (cotton) filters do not filter without the oil added. That being said, many people over oil them. You only need a little… Turning them RED is too much. Just a slight pink hue is all that's needed.

I would look into seeing if you got the "bad" floats. First step...

[WWhunter]

Thank you sir! I also suspect the floats, hence the reason I pulled the float bowl off. I will pull them both off again and double check the float height.

As for the K&N filter, I have been doing exactly what you stated, a light oiling just enough to get a slight hue of pink. Won't hurt anything to clean them again and re-oil.

It's been yucky weather the past few days and rain so my food plot work is on hold, guess I could get into the hangar and work on the plane.

[HighWing]

I rebuilt my carburetors on the first Model IV and it idled terribly spilling fuel from the vent tubes. I finally put the old float needles back in. No problems since. There was something with the new iteration of the needles. This was a while ago and I don't recall the details, but they have several needles for different applications - some black, some silver colored and some brass. I ran with the original needles for over 900 hours.

[Dave S]

Lowell,

Your experience kinda makes a case for if it isn't broke....don't fix it.

We replace the rubber diaphragms in the carb every 5 years.....Curious if anyone as ever seen one of them break or rupture?

I replaced the carb flanges for the 5 year deal and the only way I could tell the old from the new was the distinct odor of auto gas o the old ones....bent and folded the old ones every way I could but couldnt find the slightest indication of cracks.

DS

[WWhunter]

It has been a month since I have touched the plane other than pushing it out/in the hangar to get tractors and other equiptment out of the hangar for the summers work. Some medical issues have kept me on the ground also but it is time to get back to work on the plane and do some flying before summer ends and that dreadfull white crap covers the terrain.

I will have to retract part of the above statement, I did pull the float bowls off to check the floats and they looked ok. I am thinking I may take off both carbs today and make sure the jets/needles/etc. are clean and debris free.

One question I have, what slot/notch is the clip supposed to be on the main needle? Just want to make sure before I tear into it.

[Av8r3400]

If I remember correctly, the clip should be in the #3 slot, second from the blunt end of the needle.