Rebuilding a 300 Hirth into a MOD motor
This is the view looking toward the exhaust port side of the cylinder. * * * Well now, what do we have here...! This is what happens when the aftermarket point sets are used. Sometimes you can't get the engine timed right because the points are made "wrong" and you can't rotate the stator plate enough to get the timing correct. I made the slots about 1/4" longer and it was just barely enough. I also had to repair/replace the lighting coil, points, and ground wires as they were pinched/cracked/corroded. A new spark plug wire was also installed on the ignition coil.
This is the timing "buzzer" that I use. Black wire grounded on the engine and the red wire clipped to the "points" wire. With the point gap set and the dial indicator in the spark plug hole, turn the flywheel in the normal running direction and stop as soon as the box buzzes (it's not really a buzz, but more like a mono-toned whistle). Check the dial and rotate the stator plate as needed. * * * The Intertec manual lists the timing as .0126" BTDC static (retarded). Arctic Cat lists the timing as .020" static/.156" advanced. This one timed out at .014" with the stator plate fully advanced. For kicks, I took the flywheel off and locked the point cam in the fully advanced position and got a reading of .156", just like Arctic Cat had it listed. So I left it at .014" static and called it good.
Two new rubber grommets were installed in the case and the stator wires and the spark plug wire were feed through as the stator plate was installed. After the timing was set, the flywheel was torqued down (60 ft-lbs), the magneto cover plate on, and the fan housing bolted on. * * * The starter cup is now installed and the spark plug cap is put on, along with a "vintage" Champion K-5G spark plug.
Here are a couple of views of the vintage Schroeder HR-to-HD carb adapter. I found this one on Ebay.
The choke plate and shaft all polished up. The worn spots on the choke shaft were built up with solder and then turned back down to proper size. * * * Here is the Tillotson HD that will be used.
The carb was completely disassembled (including welch plugs), cleaned, and rebuilt. Close attention was paid to getting the "pop-off" pressure (for the inlet needle and seat) within spec and getting the needle arm adjusted correctly. * * * After this pic was taken, the throttle stop/cable linkage piece was changed to return this carb to a "top pull" configuration as the HD14A should be (at some point in the past, this carb was converted to a "front pull" set up).
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