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Poorly Rotax 914

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Dave.Moore(at)lr.org
Guest

Posted: Mon Oct 04, 2010 12:58 am Post subject: Poorly Rotax 914

Rotax 912/914 Gurus,  

I’ve been building a Europa for most of my leisure time for the past seven years.  Now I seem to be falling at the final hurdle.  

A few years ago, I bought a 914 with seven hours on the clock.  The engine is now fitted to the aircraft and has passed all its tests (fuel flows, fuel pressure, oil pressure, operating temps).  We are still ground running / testing.  The carbs are mechanically and pneumatically balanced and the engine starts easily (every time).    

We have run the engine through the full throttle range, up to 5700 RPM.  

However, sometimes when we advance the throttle, the engine cuts.    

Sometimes this happens before we reach the 100% gate, sometimes we get past the gate and it cuts when we push it to 115%.  At all times, there is a noticeable “flat spot” as we accelerate the engine up from about 2000 RPM to 3500/4000 RPM.  

Another troubling aspect of the engine's operation is that when the engine is started with choke (from cold) it cuts when the choke is released, no matter how much warming it has had.  The engine can then be readily restarted without choke, whereupon it will run sweetly – bar the behaviour described above…  

The fuel filters are clean and it will run happily at 4000+ RPM when it gets there.  It does not appear to be fuel pumps, both pumps give very healthy flow rates, (when tested with the fuel pressure regulator pressurised to 5.1 -5.8 PSI (per the Europa manual)).  

I have to admit to having reached the limits of my mechanical competence.  In an ideal world I would contact the local expert, who would apply their wisdom, however, I live in the wilds of Scotland (Aberdeen), and Rotax 914 gurus are thin on the ground up here (to the best of my knowledge).  

So, before I have to resort to importing a Rotax guru from England-shire, I wonder if any of you technical wizards on this forum has come across similar behaviour on a 914 (or a 912, because I don't think it is turbo related) and could shed some light on my darkness.?  

With thanks and regards,  

Dave  

Dave Moore  

XS Monowheel #550  

Aberdeen, UK  

Tel:  Day:  01224 267815.  Home:  01224 572041  

    [quote][b]

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rparigoris

Joined: 24 Nov 2009
Posts: 805

Posted: Mon Oct 04, 2010 2:26 am Post subject: Re: Poorly Rotax 914

Hi Dave



Sounds like you are running out of gas (too lean of a mixture).



First thing to do is make sure the carb is clean (jets and passages), the float bowl gaskets are not leaking (if they leak air it will cause a lean mixture) and all of your hoses going to the carb, fuel pressure regulator, enrichment solenoid, airbox and all transucers are not pinched or leaking.



Make sure the slide in the carb is not binding and the diaphragm is in OK shape.



Also do a mag check at flat spot, and apply choke at flat spot and see if that changes anything.



Be careful reassembling choke parts, mark and take pics before you disassemble.



Good luck.



Ron Parigoris

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neveyre(at)aol.co.uk
Guest

Posted: Mon Oct 04, 2010 8:48 am Post subject: Poorly Rotax 914

Hi Dave,

   Look at the throttle cable inners just as they disapear into the outers inside the throttle lever box, if you slam open the throttle, does one of the cables kink and get ''left behind'' ?

   I have seen both the symptoms you describe caused by that.

   Cheers,

   Nev.

 

 

   

 

 

   --

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Dave.Moore(at)lr.org
Guest

Posted: Mon Oct 11, 2010 5:02 am Post subject: Poorly Rotax 914

Many thanks to those who answered my plea for advice a week ago on my poorly running 914.  I really do appreciate the time you took to send such sound technical advice and such supportive advice.  (Flat spot when increasing the throttle and sometimes cutting during acceleration).  

First prize for accuracy of diagnosis must go to Kevin Dilks (He of mobile support for Rotax engines fame), who commented that the factory set up of 914’s was often too lean and that often run better by lifting the jet needles by one notch .  We did just that yesterday (after checking for bending/sticking throttle cables; leaky fuel pressure connecting tubing; debris in the carbs – all OK).    

Lifting the jet needles by one notch transformed the engine’s operation.  The flat spot disappeared, and the engine accelerated smoothly through to 100% and thence to 115% - repeatedly and without hesitation.  

(We did have a secondary scare when the engine showed signs of fuel starvation at 5000+ RPM.  However, we immediately diagnosed, found and rectified blocking fuel filters.  A big reminder, especially to new aircraft & those with refurbished fuel systems, how vital it is to check those pesky fuel filters regularly.  One of our filters was pretty well blocked with very fine, dark debris after only 2+ hours of running from new).  

I really can’t overstate how helpful everybody’s advice was.  (Nev, thanks for the tip for transitioning from choke to throttle – works a treat.!).  As well as the technical advice, it was hugely comforting to hear from others who’d had similar “teething troubles”.  I was pretty despondent last week when I sent the plea.  A day or two later I was able to assemble a list of things to check, from everyone’s advice and cheered by the encouragement from you (Take a special bow, Justin Kennedy, your note was a special morale booster..!).  Now, after a couple of days of implementing your suggestions, we appear (touch wood..!) to have sorted the problem.  

Thank you fellow Europa-ists and fellow forum-ites....!  

Regards,  

Dave  

Dave Moore  

XS Monowheel  

Aberdeen, UK  

Tel:  Day:  01224 267815.  Home:  01224 572041  

 

    [quote][b]

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