Carbie Sync problem with 912UL

[Bluey]

Hi has anyone come across any 912's with problems with carbie synchronisation? I was wondering because I recently had an exhaust crack and the trike manufacturer airborne reckons that it might be a carbie sync issue. However a test flight paying particular attention to engine vibrations didn't reveal any obvious vibrations coming from the engine. I had an experienced instructor have a look at it while on the ground and he thought it seemed pretty smooth. The engine now has 455hrs.

 

Bluey.

 

 

[eastmeg2]

Gauge Tales

 

Hi Bluey,

 

Any imbalance should be most obvious at idle & low revs.

 

How well do your CHT's and EGT's for both sides of your 912 match during flight?

 

I've often noticed that one side appears to consistently run slightly hotter and I assume it's due to that side running slightly leaner. I recently bought a carb synch kit from a USA aviation company, what the the great FX rate and all. I've yet to get around to using it but hope to find time in the coming weeks.

 

Cheers,

 

Glen

 

 

[Guest Maj Millard]

Rotax recommends two types of carb synching on the 912s. One is the mechanical method which I use, and prefer. These carbs are not at all sophistocated, unlike many twin-carb types of the past, (SU etc)that were not fitted with equalization tubes and did require synching often.

 

The mechanical Rotax method works well by simply ensuring that the mechanical side of things are identical both sides, (levers, butterfly etc), and measurements for this are all available from the Rotax maintenance manual.

 

The 912s also have an equalization tube between the two carb manifolds, and this is like an auto-synch when things are running, and assist both manifolds in maintaining equal vacume.

 

I frankly shudder when I hear people who are not really familiar with these simple carbs, start talking about synching them. They like a rebuild kit put through them around 700-800hrs, and if normal cable wear and stretch is taken care of with mechanically synching as per the manual, they will easily give you hundreds of hours of worry-free flying............................................................Maj...

 

 

[Bluey]

The EGT's when I flew on Saturday were different by around 60deg at times. However the side that was higher had a brand new EGT probe installed that day. So I don't know if there is a wearing in period with these things but I imagine that over time indicated temps should change as carbon build up occurs. I do remember the other probe do the same thing when it was replaced. However, the second probe failure occurred within a few hrs of the first one being replaced. I now have renewed both probes on the engine.

 

Bluey

 

 

[eastmeg2]

Rotax recommends two types of carb synching on the 912s. One is the mechanical method which I use, and prefer. These carbs are not at all sophistocated, unlike many twin-carb types of the past, (SU etc)that were not fitted with equalization tubes and did require synching often.The mechanical Rotax method works well by simply ensuring that the mechanical side of things are identical both sides, (levers, butterfly etc), and measurements for this are all available from the Rotax maintenance manual.

The 912s also have an equalization tube between the two carb manifolds, and this is like an auto-synch when things are running, and assist both manifolds in maintaining equal vacume.

 

I frankly shudder when I hear people who are not really familiar with these simple carbs, start talking about synching them. They like a rebuild kit put through them around 700-800hrs, and if normal cable wear and stretch is taken care of with mechanically synching as per the manual, they will easily give you hundreds of hours of worry-free flying............................................................Maj...

Hi Maj,

 

I'm pretty sure the kit I've got is an aid for the mechanical synch'ing you're referring to. I've been warned (by a CFI/L2) about pulling the 912's carbies apart before, haven't done it and have no intention of doing so by myself. As I understand it, what I'll be doing is ensuring that both sides of the 912 are working equally (or closer to it) via adjustment of the cable linkages on/near the carbs. The EGT's on the respective cylinder banks give some indication of how well they are matched, however, keeping in mind that our instruments are not certified/TSO'd there may be a margin of error in the readings being seen. The carb balancing kit should get around that.

 

Bluey,

 

I recently replaced one of the EGT sensors on another trike with a R447 (2 stroke) and am seeing that one read as much as 150F lower than the other cylinder (900F and 1050F, so appreciate what you're saying. I'm thinking of swapping the sensors around (back to front and front to back) to see if the readings move with the sensors or stay the same for each cylinder. I've got a spare new sensor as I ordered 2 so I'd have a spare.

 

The new probes are shorter than the old ones. Maybe that contributes to the lower reading?

 

Cheers,

 

Glen

 

 

[facthunter]

Change sensors.

 

The logical thing to do is swap the sensors if the layout permits, or borrow a spare and do a ground run and swap it to both sides consecutively. Nev

 

 

[Bluey]

While my EGT's show a small difference, the CHT's are usually very close typically within 5 - 8 degrees. When the plugs are new the are generally within 5 degrees.

 

Bluey