Carb teardown and checkout

Regarding the 200 hr carb inspection are we better off doing ourselves, or sending out to a rotax service provider. Asking because a friend sent out and wound up re doing when they came back as were poorly done. Just asking for your experience/recommendations on this matter.
Thanks.
Dick Seiders 120093

Hi Dick,

The 200 hr. carb inspection is just that, just taking a look. No overhaul. You can do it just as easy as anyone. If you aren't having any issues, float weight is good and the carbs sync well you won't find anything. Some buy an "O" ring replacement kit for about $35, but I don't think you need it. You should check them, but I know the majority don't. The only thing a trained Rotax could do is maybe have a set of trained eyeballs if they have seen a lot of carbs over a single individual.

Hmmmm... I wonder what Mike Busch would say about taking apart a carb at 200 hours that is working perfectly just "for a look."

If these carbs had a history of developing problems shortly after the 200 hr. mark, then I would do a rebuild. But, they don't have a history of problems.

So, if your engine is running "just fine", I wouldn't get too involved at 200 hours.

The carbs on my CT have 425 hours and are 8 years old. I did not replace anything at 200 hours and the engine still runs "just fine".

I agree with John with the possible exception of replacing the diaphragm every 5 years as part of rubber component replacement. I plan on doing that because if one cracks on the road you're stuck. I carry a spare fuel pump and voltage regulator when I'm on the road. You can't bring a spare for everything, but I try to have a spare for what seem to be the most common failures.

carb teardown and checkout

Thanks for the feedback all. My carbs are actually at 270 and change and all I have done so far is peek at the bowls to be sure they were clean, and while I did find a small piece of rubber from the gasket or floats in one I didn't go any further. With my 5th Cond. Insp. coming up I felt I might go further since I have to remove the carbs to replace all the rubber attachments anyway.
Dick Seiders 120093

Inspect the carbs

After having taken the Rotax maintenance class and seeing first hand the way the carburetor?s parts can wear, I feel the 200 hour inspection is important. We saw first hand the effects of vibrations caused by poorly synchronized carburetors. The excessive vibrations can really cause accelerated wear on the carburetor?s internal the parts.

We saw a few examples such as: A jet needle almost cut in two from circlip vibrations cutting away at the grove in the jet needle. Groves worn into the float bracket pin and a thinning of the float bracket?s metal. Heavily worn float needle valves. Scuffing of the carburetor piston and carburetor body.

Take a close look at ALL the carburetor?s internal parts, not just dirt and particles in the bowl.

John,

Were there any symptoms, or was the failure mode a ticking time bomb?

Rich

Rich-

I would say more like a ticking time bomb. With the exception of the very worn float needle valve which most likely caused a very high fuel level and thus a very rich running carb, all the other parts would have still been quite functional. The scariest was the circlip wearing a grove almost all the way through the needle jet ... what little metal there was remaining, was awfully thin. That needle jet could have easily been ingested had the circlip been neglected much longer.

John,
I'm guessing you ment to say the needle would be easily ingested if the circlip wore through the needle. This actually wouldn't happen. The needle simply falls down into the main jet/needle jet stack and sits on the float needle. If that would happen in flight a high power setting can still pull the needle up far enough for enough fuel to run quite smoothly but throttle back and the needle drops down, shutting off fuel to half the engine and it gets really rough. I had a circlip fail a couple months ago and this was my experience.

Usually the excessive wear in a carb like needle wear or float wear comes from vibration.
This is caused by either poor carb sync every 100 hrs. or Annual or idling too low an rpm for long periods over time. The needle can also have excessive wear from people getting into a carb and removing the needle and losing the small "O" ring that is supposed to be on top of the needle. The really old carb sets didn't have this. Carb diaphragms should get replaced during the 5 year rubber change out or during a carb overhaul.

The carb inspection is easy and you do not need to mess with the cables and their adjustment.
Just remove the throttle arm by removing the 11mm nut and do the same for the choke. Now just take the two screws off the top of the carb off and lift the top off. Loosen the rubber carb flange clamp and push the carb straight back and now it's in your hands and you haven't messed with the cable adjustments at all. I would however always do a carb sync if you pull carbs off and tinker with them.