What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

New Page 03-02 Carburetor Synchronizing Tool

B

BigJohn

Well Known Member
:confused:I've compared the new Builder's Tool Requirements to the old. Most of the stuff the've added is self explanatory, but what in the world is a "Carburetor Synchronizing Tool"? Anybody know?
 
I'm guessing the Rotax has dual carbs, and the amount of vaccume they draw needs to be the same. Similar to multi carbed motorcycles. Basicaly, a pair of vaccume gauges or mercury collums. Or for engines with only two carbs, a differential gauge works. Google Twinmax and Motion Pro carb stick for typical ones use with motorycles.
 
Last edited:
Mike has is right. The Rotax 912S has dual Bing carbs that need to be "synchronized" when hooking up the throttle cables, and every annual. It is a simple procedure like Mike describes. Basically, you have just adjusting the carb throttle cable lengths so the carbs are opening and closing together, thus synchronized.

Any motor cycle shop will have the gages or mercury columns you need to do the job. Here is a link to Califorina Power Supply (CPS)

http://www.rotaxparts.net/scripts/prodView.asp?idproduct=1297

This procedure requires the engine to be run to verify that the carbs are synchronized so great care must be taken when do this test / adjustment. ALL adjustments are made with the engine off, then test the adjustments by running the engine again. Trial & error method only.

Any time you work on the carb, replace a carb boot, ect, you'll need to do this again. It is not a big deal at all, just something new due to having dual carbs. Working on the Rotax 912(s) is a real pleasure IMHO. There are many tricks of the trade that I'm sure will come up as the RV-12 fledges from the builder's nest.

Hey Mods, maybe this is a good time to start a Rotax forum?
 
Last edited:
Bikers use em alot...mostly Morgan's (English)....about $100....or you can make your own.

While we're at it...whats the best place to buy all of the glass stuff...I've never done any plastic...no idea where to get the "e-glass" etc. Help!!!!
 
Do invest in the carb synch tool- you will use it at first engine startup and every annual thereafter. The 912 ULS is one of the smoothest running engines you will ever work with- but only if the carbs are synched- if they are not, the engine can do serious damage to itself in fairly short order. What happens is that each carb serves the two cylinders on its side- if they are not drawing the same amount of air for a given throttle setting, the two halves of the engine fight each other. The difference between a synched engine and one that isn't is dramatic! My 912 in my Rans has 230 hours now, and just seems to keep getting better and better. The synch procedure is not difficult, but don't even think about skipping it. Steve P.S. You can get the tool from Lockwood in Fla.
 
steve wyman said:
Do invest in the carb synch tool- you will use it at first engine startup and every annual thereafter. The 912 ULS is one of the smoothest running engines you will ever work with- but only if the carbs are synched- if they are not, the engine can do serious damage to itself in fairly short order. What happens is that each carb serves the two cylinders on its side- if they are not drawing the same amount of air for a given throttle setting, the two halves of the engine fight each other. The difference between a synched engine and one that isn't is dramatic! My 912 in my Rans has 230 hours now, and just seems to keep getting better and better. The synch procedure is not difficult, but don't even think about skipping it. Steve P.S. You can get the tool from Lockwood in Fla.
Click to expand...

Excellent description Steve, as to the "Why synchronize?"

Lockwood is an excellent source for parts, service, and great seminars during the big airshows. Their web site is currently down for much needed upgrading IMHO.
 
you do need to balance the carbs. There is a big sequence. I basically put the throttles to full throttle, back off just a bit, than make sure both carbs are opening the same by measuring the distance to full throttle, like .020 on each lever to stop. That will get the engine started. Than you need to balance with vacuum guages on each side, there is a left and right, one for each carb. You also need to block off the tube that goes to each side. You can put a vacuum guage on each side. Or do what I did. Take all the junk off, fuel return and junk and put a straight hose between the left and right side. I never had a problem with starting. Oh and my engine is now 2 months old, my other engine was flown for 2000 hrs and it didn't need it either. But anyway, once you hook up a vacuum to each side you can go through the trouble of restricting the vacuum hose so the needle doesn't bounce all over the place or you can do like I did.

Get a Twinmax. This unit is electronic, cost about 90 dollars and is accurate.
I do mine on every oil change, 50hrs. That equates to about 6 times a year for me.
 
As mentioned, the Twinmax is an electromic tool that measure the vaccum on both carbs and swings a needle left or right. When sync'ed, the needle is in the middle. A similar device can be built for $2 as pictured below. One long hose with a loop in the bottom, each end hooked up to the vaccum port on each carb. The carb with more vaccume will draw that side of the fluid column a little higher. Tune untill both columns are equal height. Use ATF for the fluid as its easy to see and wont hurt anything if you suck it through your motor like mercury would. If the fluid is jumpy, put a restrictor inline on each line going to the carbs, a 1/16" hole should work, or put an inch of brass tube inline and pinch each down or solder one end up and drill the 1/16" hole. BMW, Triump and other twin motorcycle mechanics have been using this setup for decades.
manometer.jpg
 
Rotax Info

The website mentioned above, www.rotax-owner.com not only has videos about selected topics of importance, but also all Rotax manuals (Operators, Install and Maintenance) are there for downloading. Also all Service Bulletins are there. Lots of good information there.

To stay up to date, you should sign up for automatic notification of new items on the website. It's surprising how often they update things.

The various Rotax dealers (Lockwood, Leading Edge AirFoils, Mississippi Sport? and California Power Systems ? - I not sure if that's all or the exact names of the last two) give telephone support and are very knowledgable. The Canadian distributor in Vancouver is also very helpful.

Some of the dealers offer schools, usually a couple of days and pretty reasonably priced - a few hundred dollars. Everyone seems to think they are well worth attending.

There is a Matronics Rotax forum with a couple very knowledgable trained mechanics usually answering questions.

Be sure to read the info about oil and coolant for 912. AeroShell Sport works well. It is important to use an oil with gearbox additives, like many motorcycle oils since the engine oil lubricates the gearbox too.

I use a Twinmax to sync my carbs. Works well, doesn't leak ATF and is easy to use.

Jim Butcher
Europa XS Rotax 914
 
You must log in or register to reply here.
Back
Top