Carb rubbers

[Monocock]

I thought I would add my recent experience with 912 carb rubbers here as I am aware they are considered a weak point on the set up.

I recently had a carb work loose on my 912s and I loosened off the clamp, re-positioned it and flew some more. Within an hour or two it did the same again. The carb body came away at the base but the top part of where it clamps it remained in the socket. I took the socket off and was amazed to find the internal retaining rib had sheared off on the lower section of the rubber and there was also a small chunk of rubber missing.

The rubber socket was replaced and and I am amazed at how much smoother the engine is running. I am sure there was air getting past the clamp and affecting the mixture on that side and she is sewing machine smooth again.

There were no visual clues from the outside of the carb rubber that there was a problem lurking inside. From now on I have decided to consider these rubbers as a part of a 25 hour inspection as I could not believe what condition they were in inside.

Just thought this might be of use, especially to the 100hp brigade as some of those hard starts can't do much good to items such as this. I had a GSC prop on her for 15 hours a while back which vibrated like a road roller and I think that might also have contributed to the problem too.

[Dorsal]

Thanks for the tip, will add it to my 25 hr as well.

[sdemeyer]

I went through several sets of expensive Rotax sockets within a year time frame. Then I bought JBM sockets at half the cost and have had no more problems. The JBM sockets are very good quality and are much sturdier.

[jtpitkin06]

Those carb sockets have always concerned me. Have you considered doing a solid mount, or supporting the carb with a supplemental bracket?

Good to see you caught it in time.

John Pitkin
Greenville, Tx

[Dorsal]

I am curious if anyone has had problems with these who use the Rotax airbox? The airbox appears to do a reasonably good job supporting the other end of the carb.

[sdemeyer]

Good to see you caught it in time.

It is on my daily, before flight checklist. I had a real problem with the carbs being thrown off at startup. I ended up taking the KF to a Rotax dealer because of the carb issue but everything checked out fine. He did end up rebuilding my gearbox which helped some. The problem I see with the Rotax sockets is you cannot tighten the clamp because of the spacer. The JBM recommends ditching the spacer and tightening the clamp good and tight. I have not had a cracked boot or thrown off carb since using the JBM sockets, about 30 hours ago.

[SkyPirate]

the purpose of the rubber between the carb and motor is to reduce vibration at the carb,..on my model 2 I put safety wire from the motor to the carb to hold it from vibrating out of the rubber,..but I still checked the rubber for cracks often.

Chase

[Dave S]

Got the rotax airbox on our 912ULS - neither end of the carb can wiggle at all with the airbox in place - Airbox clamps to the top center of the ring mount.

Also - the newer Rotax air socket clamps have a bushing that assures the correct amount of tension on the socket.

Airbox is supposed to be good for 5 HP everything else being equal.

Airbox provides an alternate air intake also.

Cheers,

Dave S
St Paul, MN
KF7 trigear

[Monocock]

Have you considered doing a solid mount, or supporting the carb with a supplemental bracket?

Have a look at these, supplied by Sting Aircraft. They attach to where the front screw normally goes on the front of each carb "hat" and then a bracket holds the whole thing secure.




A picture of one installed is shown half way down this article:

http://www.mcp.com.au/sting/newslett...sletter-9.html

[dholly]

Did anybody ever follow up re: those Sting carb brackets? If not, I might be able to email an Avid owner Down Under to check availability and $$$. Not worrying about your carbs falling off... priceless!

Also... I've been pleased with the JBM 582 carb sockets and decided to replace the sockets on a new-to-me 912ul as a preventative measure.

w00t, I just found out the little suckers cost about 2x as much!