yet another "rough running" thread

Problems can be very frustrating.  I went back and reviewed your thread and have a suggestion.  Given the age of the engine and hours perhaps it is indeed a fuel issue.  On the 912 series Bing 64 the "choke" is actually a small carb itself in many ways.  Kindly try running it with ½ choke on.  Leave it on and try running for a while to see if the problem is better or worse.  The 3000 to 4500 RPM range is lean for the most part and if you perhaps have changed prop or pitch on the prop it may just not have enough fuel.  (a lean miss can happen when you have the needle set incorrectly for example) 

Check your MAG drop at 4000 on a warm engine.  If it is less than 300 then this might just be another rabbit hole but may be worth a try.

Cheers

Hello

when I read your post I saw that there are questions and answers … You wanted to find the problem you have first to research it (without changing parts an so on) after that you can make hypothesis and have diagnosis that the rational way to fix the issue otherly you will change a lot of parts and finally may be you find it…may be not.

Kristof 

www.hceaero.org 

Sean Griffin wrote:

Long shot:  A brand new spark plug has been known to be a dud. Re install the old ones and see if the engine still runs rough.

Thanks, Sean.  Yes, it is, but we're open to long shots at this point!  So we popped out a fresh plug and made sure it looked happy and then put it in at 1T and proceeded to "shift column right" all around the engine.  No swap made things any better :-(

Rotax Wizard wrote:

Problems can be very frustrating.  I went back and reviewed your thread and have a suggestion.  Given the age of the engine and hours perhaps it is indeed a fuel issue.  On the 912 series Bing 64 the "choke" is actually a small carb itself in many ways.  Kindly try running it with ½ choke on.  Leave it on and try running for a while to see if the problem is better or worse.  The 3000 to 4500 RPM range is lean for the most part and if you perhaps have changed prop or pitch on the prop it may just not have enough fuel.  (a lean miss can happen when you have the needle set incorrectly for example) 

Check your MAG drop at 4000 on a warm engine.  If it is less than 300 then this might just be another rabbit hole but may be worth a try.

Cheers

Thanks, Wizard.  No kidding!  We're ready to pull our hair out over this.  The short form is that it ain't over yet *sigh*

We tried the choke test, which I think you're describing, and we couldn't find any particular improvement from running with or without the choke; it just gets richer and, well, throatier.  It's been long enough with enough test runs, though, that we'll need to go back and do it again in order to take fresh notes.

Meanwhile, we can't get to 4k rpm in our little plane because it starts dragging the tires along the asphalt! :-)  But we do runups at 3600.  So far, they're always just 120 (ie one step) indicated on this digital tach.

There's every chance we could have changed the prop pitch; when we thought we had this done we pulled the prop for its ACI, and although we're quite OCD about positioning I could believe a half a degree off.

So we'll keep at it ...

Kristof HUCHET wrote:

Hello

when I read your post I saw that there are questions and answers … You wanted to find the problem you have first to research it (without changing parts an so on) after that you can make hypothesis and have diagnosis that the rational way to fix the issue otherly you will change a lot of parts and finally may be you find it…may be not.

Kristof 

www.hceaero.org 

Bonjour, Kristof, et merci!

You certainly make a good point, and we also try to alter only one thing at a time in order to know what effected a change we might see.  We did a lot of reading and research before and at each step along the way, though, in order to know what to check and how in order to then know what to change/alter/replace and how.

If you see something we've missed, please do provide any tips you may have.  All we want is for this to get better, and I don't even mind looking stupid along the way! :-)

Merci beaucoup