Ottawa Detent Modifications`

To remedy the problem, I took the detent arm off the engine and cut a 7/16th inch thread along the thick part of the arm to a point just after the cotter pin hole. I then threaded on a 7/16th nut which (not knowing the technical term) is like a castle! Thanks to Dave Croft who told me this is a Castellated nut. This will allow me to use a cotter or mechanics wire to secure the nut and stop it moving. With this arrangement the spring is now always under some tension meaning the detent has to move much less to trip the mag.

The Ottawa has a lever just under the mag which alters the detent timing by about 5 degrees for each notch. I was told that the first position is for stop (and the mag cannot be tripped in this position). The second position was for run, the third for start and the fourth unused.

Originally I followed directions I had been given and timed the engine so that it fired right on TDC in the third position on the start/run lever to start the engine and then about 5 degrees before TDC in the run (second) position. This was always touch and go, and would often end up in a situation where the engine would fire in the start position and not trip the mag in the run position. I took apart the mechanism and decided I'd been given bad advice in the first place. I've now retimed the engine so the first position stops the mag tripping as before (stop), and the second postion fires at TDC for start, and the third position fires about 5 degrees before TDC for run. The fourth postion, as it happens fires about 10 degrees before TDC for run with giant yellow flames :)

To cut a long story short, the engine now runs really well and starts first time every time (unlike before, as people who saw me at Tulare California can attest. Basically what the modification does is that the detent spring is now always under a little bit of tension instead of flopping around everywhere. Also there are no loose washers or cotter pins to move - the nut held in place by a cotter (just luck allowed me to use the original hole!) is rock solid. The mag fires every time now like it should - before the throttle governed Ottawa was pretending to be a hit and miss!