Sputter because of Bully Hawk soft start

Phillip...

First, just disconnect the Bully Hawk and see if it makes any difference.  The only thing that it is doing is a 3 to 5 second delay in the advance of that module. 

Or second, try starting on the other module alone and run the engine up.  Then shut it off and do the same with the one that has the Bully Hawk...see if you have a difference that way.  A few options to check that circuit. 

Replacement is easy if he is not paying for it.  Just saying. 

I note you said previous owner....did he tell you that with the Bully Hawk you should start  on that circuit first.  Wait about 10 seconds and then switch on the other?  Only the module that has the Bully connected has the timing delay, the other one advances before you hit idle speed.  

Cheers

Thank you for the reply.  Yes, we disconnected the Bully Hawk and it caused the engine to "kickback" as the tech called it. 

The previous owner had a starting procedure of "prime first, with Master on and Switch off, then turn the ignition switch on "both and start".  This method usually always caused a shutter and a kickback.  The previous owner always used the prime and both and had never turned on the Bully Hawk module for starting.

The tech checked which module to start on and told me I should always use the Left module to start and turn to both after a few seconds, as you mentioned. When I used this start procedure, the engine started smoothly with no kick back and then I did the run-up and switched to R/L, and on both modules; the engine ran well.  Since the engine has had a sputtering problem and I have gone through a checklist of possible causes and thought it was fixed, on my last take off the engine sputtered.  Therefore, the tech thinks it is a bad Bully Hawk.  He told me I could disconnect the Bully Hawk, but there was an increased risk of "kickback" which damages the engine and therefore, for the life of the engine in his opinion was best to get new Rotax modules.  He had a similar experience with the Bully Hawk on his Rotax and since he put on the new modules, he has not had a problem with starting or sputters/rough running.  

The tech told me he would replace modules for me at "No Charge".   He assisted me with the checklist for the sputter and is very helpful.  

Thanks again for your comments.

Hi again Phillip

I have looked up the SB on kickback from long ago.  This issue was mostly due to lack of gearbox maintenance (shimming) and was made worse with heavy mass props.  The bottom line was it would damage the sprag clutch that is internal in the starting system.  The best way to determine if your sprag was damaged, or is still damaged, is follow the test on the electric draw cranking amps of the starter motor.  If the draw is low it indicates the sprag is slipping and you have low crankshaft speed that allows kickback.  

If your system kicks all the time with the Bully working then in my mind start by getting your gearbox serviced.  Test the starter draw to see if the sprag needs replacement.  The timing delay was always a bandaid for the real issues, it did work however. 

Cheers

Sorry, you need to have the full file for the certified S version to get the whole thing....

Thank you for the additional info.   I will look at this.  It did kickback, but not all the time.  Mostly on cold starts.  However, after the engine warmed up, it started immediately.  I was surprised that during my review of the checklist, there was no mention of using the Left "mag" to start and then switch to both, which when I started on left and switched to both there was no kickback.

I am thinking about going ahead and getting the new Rotax modules, which include a soft start.  I know it is expensive, but I want the best performance in that I hope to keep the plane for a long time.

Do you think at this point in time it would be worth it?  Others have told me to disconnect the Bully Hawk and start on both with no prime, which is stated in the Rotax manual.