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silverbear

The Boy Who Never Grew Up
Jul 9, 2009
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northeastern Minnesota
If it were me I would use the 79cc Harbor Freight Predator engine. As I mentioned before if you watch for a sale on them it will bring the price down to around a hundred bucks. For a brand new engine, easily replaceable, that's hard to beat. It is not high revving, has a lot of grunt and is super easy to start... an easy pull in other words. I've had one matched up with a Qmatic transmission and am currently running the 99cc version of the same engine also matched up to a Qmatic. With a trike you have lots of room to set up a simple jack shaft utilizing most any automatic clutch... even a used one from something like a snow blower would work well. No need to go the more expensive route of the Qmatic or similar transmission. Keep it simple and inexpensive. High performance you do not need with a lower mph. As mentioned elsewhere on this thread, 20 mph or so is probably about as fast as you want to go. More important is reliability, simplicity of operation and safety. Geared lower for a top speed of say 25mph wide open throttle (even though she won't be going that fast) it will be able to easily pull out from a dead stop and climb just about any hill. No pedaling to get the motor started or pulling out from a dead stop. Twist the throttle and go. Nail those things and your wife will love her trike. On a tight budget that's what I'd do.
SB