Jerry & John, Thanks for the feedback. It makes sense about fouling up the plugs with such a rich oil mixture. I ended up upgrading my 2-cycle Tohatsu with a 4-cycle, since I felt bad about the oil slick I left behind. The Chesapeake Bay has enough issues without me contributing. Speaking of the Tanaka, I have a Cruise N' Carry 1.5 hanging in the garage. It too is an oil slick waiting to happen. But I'm holding on to it as my planned power source for my latest restoration project. I am restoring a 1972 vintage M-5.5 Montgomery pram. I'm not sure what the intended power source was for this little tug, since it didn't come with oarlocks and it wasn't set up as a sailing pram. I'm hoping to install a pair of oarlocks during the restoration. Of course, I haven't attempted to sit in the dinghy in a rowing position to see if manual propulsion is even possible. There is no cut out under the rear bench for my feet, so my knees might be in the way for rowing? Details, details..........I'll just figure it all out when I get there. lol Besides, since the M-5.5 wasn't in production for long, maybe it wasn't practical for actual use? Jerry, maybe you could jump in and give a brief history of the M-5.5? I once tried to use a trolling motor to power the pram, since it was small & lightweight. Of course, when I added the battery, the water nearly crested the gunwales. I should have just hung that 4hp Evinrude off the back..........it would have been lighter! lol Skip -----Original Message----- From: John Schinnerer <john@eco-living.net> To: montgomery_boats <montgomery_boats@mailman.xmission.com> Sent: Sun, Aug 13, 2017 12:21 am Subject: Re: M_Boats: 3.5 tohatsu for m17 Speaking of tiny light motors...what I've been getting by with on my M17 is a vintage 1980's Tanaka 1.75 (sold under AquaBug brand - they also sold under some other brands I think including their own name). It's a short shaft so even on the pivoting mount I have, would be no good in swell or chop (I lowered the mount board an inch more just to get it low enough to work at all). Needs weight aft in cockpit to keep the exhaust under water (just above prop). Centrifugal clutch, and swivel 180 deg. for reverse. Probably wouldn't last long in salt water, and I wouldn't want to have to trust it on big water far from shelter in any case. Just getting by for now. It's enough to get in and out of a slip if the wind is just the wrong way to sail in/out (usually can sail in/out where she is this month, Howard Prairie lake in S. OR, I have a slip bow into the "usual" wind). And enough to motor back a ways if the wind just totally drops. Haven't measured it but I'd guess it pushes her 3.5-4 knots at just under full throttle. It's a weed whacker with a prop shaft & tiller arm, basically. Simple & light, haven't weighed it but I'm sure it's under 20 lbs, probably 15-17 lbs.. From my experience with auto motors, ditto what Jerry said, if the motor is built with a specified RPM range, running it continually up near the top of that is not a major issue. It's built for that. It might use a bit more fuel, and be a bit noisier. The old air-cooled VW is a classic example - runs up around 4000+ at freeway speeds, and will do that for a long, long time with basic maintenance and kept from overheating. Those motors were used for industrial applications also, running many days straight at high RPM for many years of service. I'm not saying run at max revs all the time is great. But 7/8 or 9/10 of max revs is not much different, to the motor, than say 2/3 revs. And on 2-strokes, lots of slow running definitely fouls plugs quicker (oil in the fuel mix accumulating faster on plug). Likewise for older cars (carburetor ones) driven only around town, the cylinder heads carbon up quickly without some high speed running to blow it out. The old-days fix was to rev 'em up and slowly pour some water down the carb, the steam would break the carbonization loose. Tohatsu's break-in spec for their small outboards includes running them fairly hard fairly early on - to seat the rings, which won't necessarily seat properly without that. cheers, John S. On 08/12/2017 12:40 AM, jerry@jerrymontgomery.org wrote:
I don't claim to know what I'm talking about, but I suspect that the motor doesn't really care how fast it's being run. I grew up with outboards and I remember carbon problems with motors that were not run fairly hard. 25s and 40s were as big as they got when I was in hi school, and when used for water skiing they would last all summer w/o changing the plugs, but if we did much fishing, new plugs every few days.
I wish Honda or someone would make a 1 or 1 1/2 that weighed about 20 lbs. My friend Tom Van Atta in Tucson used to have an ancient 1 1/2 Johnson; it did fine but it needed full throttle on a 17. I have an old Johnson leaning against the wall in my living room (!) that I might fix up some day. A couple of years ago a good-looking young gal (maybe about 60) came by my shop and asked if I fixed motors. When I said "no" she gave it to me. It's got the old wind-up rope starter like one I had when I was a kid. We lived on the Williamette River and in the summer when the river was low there were many gravel bars; I could change the sheer pin with my eyes shut. That motor definitely got run wide open, year after year. Seems like it was 1 hp but I really don't remember since that was about 70 years ago. I do remember that it was important to put oil in the gas.
... -- John Schinnerer - M.A., Whole Systems Design -------------------------------------------- - Eco-Living - Whole Systems Design Services People - Place - Learning - Integration john@eco-living.net - 510.982.1334 http://eco-living.net http://sociocracyconsulting.com