The M91 vertical hit and Miss is a nice little engine, but it’s not without its fiddly aspects. With a bit of work, it can be a fun toy.
If I had it to do again:
I’d ignore the teasers advising Zippo fuel. Zippo works, kinda, when planets align, but it’s not exactly the most energetic of fuels, so starting routines can be frustrating unless the mixer is spot on adjusted. I fought with getting the engine to start and run without frequent messing with the mixer, and frustrating sessions of flooding it, etc. Read on for the current set up. The less than energetic zippo fuel also made ignition battery life lousy. The ignition had to be pretty hot to reliably start on zippo.
Much rope pulling will tear the rubber handle off the rope, and the pulley notch may cut the knot off the rope. I’m using a chunk of 5/16 dowel and a bit of cord that began life as a draw string. A round file deburred the notch.
The cheese box base is fruitless. Longer, lower, heavier, wider. Stopping’ the hoppin’. Maple is your pal.
When, not if, things come loose, the grub (set) screws are soft, roughly chinese number one mushy steel. You will tear the heads out trying to snug them. Buy an assortment of quality metric set screws with deep pockets and replace the originals the first time they slip. Life is simply too short.
A spark plug wire snap on terminal end fabricated from springy brass is your friend. A bit of fuel tubing makes for a boot.
Oh, fuel? I broke down and bought tru fuel, synthetic racing fuel, four cycle blend, and add about three drops of MMO per ounce. Done.
Even after sitting a month almost empty, thumb the mixer, give the flywheel a twist, ignition switch on, pull rope, enjoy. The much lower flash point and reasonably not too unpleasant fumes aren’t bad.
On that note, a 200cfm computer fan running on 110v, mounted into a cardboard box, add a dryer vent flapper and duct hose, mount in window, yer in business to ventilate your test area.
Don’t tell anybody, but my M91 is on my kitchen table. It’s fun to just flip the switch, give it a spin with the rope, and have it start and run nicely with one pull. I don’t run it long like that, but it’s fun.
Once sorted,