Mikuni Carburetors for Rotax 912ULS ?

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Mikuni Carburetors for Rotax 912ULS ?

Postby marl59 » Thu Feb 11, 2016 12:44 pm

I wanted to ask my fellow Rotax owners if they or anyone they know have ever explored the possibility of substituting a pair of new Mikuni carburetors for the problematic Bing 64s on the Rotax 912 engine. I was looking at a Mikuni TM36-68 pumper carb on a guys 500cc motorcycle yesterday and it looked like a great set up. I took some rough dimensions and it looked like it could be made to work with some innovative massaging. The first question that comes to mind would be high altitude operation. I have used Mikuni's over the years in motorcycle operations and they have always been solid performers. I haven't checked hard dimensions yet to see if the 36mm would be the right one for the Rotax intake boot but Mikuni has many models in various sizes, so I'm pretty sure one that would fit and have the proper CFM flow for the Rotax. The Mukuni's sell for about $280. Here are some adaptability items that would have to be addressed:
Crossover tube adapability
Throttle cable adaptability
Choke cable adaptability
Intake & air filter boot adaptability etc.
Proper jetting.
Any thoughts from the community would be appreciated!
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Re: Mikuni Carburetors for Rotax 912ULS ?

Postby Av8r3400 » Fri Feb 12, 2016 6:30 pm

What's problematic about the Bings?

There are tens of thousands of them operating just perfectly. They are simple, easy to work on and matched perfectly to the engine.
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Re: Mikuni Carburetors for Rotax 912ULS ?

Postby marl59 » Mon Feb 15, 2016 11:11 pm

Carburetors are pretty simple. I have been trying to get mine to stop leaking for several months now. The floats I replaced were around $100 for the pair and there are 4 of them, still leaks. The float needles I replaced were around $40+ each, still leaks. The seats will be replaced next which I will have to take to my Rotax mechanic to do so it will end up costing more, hopefully no more leaks. So I have to leave the gas off when the plane is not running. I can do that. When the is throttle closed too hard against the light metal stops, they go out of sync. My tail wheel instructor did this so hard on one of our training flights that the engine wouldn't idle after we landed. Had to re-sync the carbs. The replacement cost is around $1,200 for each of the carbs and there are two of them. And I agree, there are lots of them in service and they are simple to work on. And I like the altitude compensation feature. I just hate the overpriced parts. So that's the reason I wanted to put the question out there to see if anyone had explored the Mikuni option. Thanks for replying!
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Re: Mikuni Carburetors for Rotax 912ULS ?

Postby FlyerChief » Tue Feb 16, 2016 12:21 am

Have you installed carb cable stops to prevent them from being pulled too hard?
Carb Cable Stop.jpg

They tighten in position with an Allen screw ... simple but effective.
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Re: Mikuni Carburetors for Rotax 912ULS ?

Postby marl59 » Wed Feb 17, 2016 12:16 am

No I haven't. I didn't know they existed. Great idea! Where can I get them? Thanks!
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Re: Mikuni Carburetors for Rotax 912ULS ?

Postby gkremers » Wed Feb 17, 2016 10:49 am

Lockwood or McFarlane has them
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Re: Mikuni Carburetors for Rotax 912ULS ?

Postby jak » Wed Feb 17, 2016 8:57 pm

The ones in the pictures come with the McFarline cables but any cable stop will do. Jak
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Re: Mikuni Carburetors for Rotax 912ULS ?

Postby SheepdogRD » Thu Feb 18, 2016 7:31 am

You can find them in the aviation section of your local auto parts store. Dorman 03336 is an assortment of six stops in three sizes for $3.

Cable Stop - Dorman 03336.jpg
Cable Stop - Dorman 03336.jpg (3.99 KiB) Viewed 1768 times

Summit has them (http://www.summitracing.com/parts/rnb-03336) for $2.69.
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Re: Mikuni Carburetors for Rotax 912ULS ?

Postby marl59 » Thu Feb 18, 2016 12:41 pm

Thanks guys for the feedback. I will order some cable stops and if I decide to experiment with the Mikuni carbs I'll post my results.
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