Curious how to determine if I have the correct breaker cam in my NS2 on my 37ci motor.   Here's why I ask, my motor will start with fully advanced timing, but it is only running on the front cylinder at that point.  When I retard the timing all the way it begins to run on both cylinders, rather poorly but both are firing.  When I pulled the rear head and measured where the piston is (fully advanced) when the points open I find the points don't open until .1697 BTDC, so a little late.

(trying to avoid opening the cam case to adjust the timing gear!)

The 45° cams are stamped with the number 45 on the face. I dont recall if they also have the letter R stamped as well.  All 42 ° cams are stamped with the letter R only.

I would agree with Phil, check the timing on BOTH cylinders.  IF the rotor is timed correctly and the rotor indexing flange is installed correctly, the wire coming from the front of the cap should go to the rear cylinder, rear wire to the front cylinder.  When checking timing, also check that the rotor is pointing at the correct wire connection for that cylinder.   I would shoot to get both cylinders firing at  3/8 to 7/16" BTDC, both as vlose as possible to the same number .

Gene Harper

Thank-you for your replies.  The magneto was rebuilt a few years ago and when we mounted it in the bike it was carefully timed with both cylinder heads off.  Now it has only run less than an hour since newly rebuilt, and since the rear cylinder wasn't firing with the spark advanced, I pulled the rear head and found the BTDC value listed above.

BUT...(and this is a new discovery) I went back to the invoice for the magneto rebuilding and found the note on the invoice stating "clockwise" rotation.  I'll be contacting the rebuilder tomorrow, perhaps the magneto is set up for clockwise rotation???

Hard to wrap my head around how a magneto set up for clockwise rotation might behave when it is run in an anti-clockwise rotation.  I'll report back after I discuss this with him!