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Old 10-02-2010, 01:17 AM   #1 (permalink)
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Homebrew scooter, ~120mpg

This started out as a "Hey, that could be fun" project, built on a budget of approximately nothing, from junk and spare parts.

About as low-tech as you can get, never built with fuel economy (or road use!) in mind, but at a steady 15mph or so I decided to see what kind of economy it would pull- as accurately as I could measure it would do 110-120mpg, that dropping to about 20-30mpg flat out at about 25mph.

The engine was a 1955 model 75cc Suffolk Iron Foundry sidevalve engine. Static points-and-magneto ignition, Zenith updraught carburetor.
Compression ratio raised from 6.0:1 up to 11.5:1, internally polished, timing adjusted to peak at about 4500rpm. New rings. Long stroke for good(!) torque. Carburetor adjusted to richer than stoich for better performance, easy to adjust lean. Toothed belt drive to the clutch to quieten the drivetrain, chain drive to the wheel. Approx. 12:1 reduction, what let it down was the gearing.

Local kiddies stole it unfortunately but the legacy of the Hardly-Davidson (yeah, it got named) lives on to prove it doesn't have to be high-tech to actually work quite well. That and it made me wonder what it could do if a bit of high-tech were to be applied to it...

I'll post pics when the forum allows me to.

--Phil

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Old 10-02-2010, 04:45 AM   #2 (permalink)
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sounds cool, i'll be watching.
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Old 10-02-2010, 11:31 AM   #3 (permalink)
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Phil welcome to the site. Sounds like a really cool project. Look forward to the pics and following the development.
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Old 10-02-2010, 02:15 PM   #4 (permalink)
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Quote:
Originally Posted by PhilA View Post
...at a steady 15mph or so I decided to see what kind of economy it would pull- as accurately as I could measure it would do 110-120mpg, that dropping to about 20-30mpg flat out at about 25mph.
Is this 20-30mpg a typo? It can't be that bad!
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Old 10-02-2010, 03:47 PM   #5 (permalink)
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Hey all

Here's the project, as-was.



That's a much younger me (that was back in 2004) on the thing.



Close-up of the back.

Sadly this project RIP due to some kids who thought it was theirs and took it from outside my house one night in 2006.

I'd love to reproduce it, or something like it, to try again with a few other things in mind that I'd had planned for the original but never got to doing.

It'd most likely end up with a Kubota, Tecumseh or Honda engine, or better still a small singlepot diesel. That and higher gearing on a planetary reduction gearbox.

Oh, and to answer your question, it did drop to about 30mpg at wide open throttle (25-30 mph), mostly because it ran out of revs due to valve bounce at close to 7000rpm. Keeping it running with the throttle mostly shut was really quite economical at about 3000-3500 rpm. Stood up it wasn't so good but inverse-square of wind resistance was really killer!

--Phil
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Old 10-03-2010, 04:23 AM   #6 (permalink)
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good luck with whatever you decide on building. i had one kinda like that many years ago. it was a fun little sucker. anyway, good luck, i'll be watching.

also, you might want to check out (minidoodle.com), ya know, just for some ideas.
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Old 10-03-2010, 09:16 AM   #7 (permalink)
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Nice looking scooter!Too bad it was stolen.

PhilB
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Old 10-03-2010, 03:10 PM   #8 (permalink)
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Apart from the scooter frame itself and a few lengths of strip metal, that was all bits of lawnmower...

I see people using lots of types of engines for minibikes and scooters. I have a few engines around here, an old weedeater (not sure how well that'd do but it'd probably work quite well for an assistive engine for a bicycle) and a chainsaw motor, which would be a bit more promising but I'm not sure I could tolerate the two-stroke wail.
The scooter pictured there had no muffler, simply a large expansion tube (1-into-2) with some steel wool stuffed into one of the pipes when it needed to run more quietly.

With the choke pulled part out to idle lumpily it sounded like a miniature Harley, hence "Hardly Davidson"...

I'm sure something more tuned would have worked better but it was economical and fun, which to me is a win-win situation!

I think engine assist bicycle is going to be next up. Living in the flatlands does have some benefits, 3cc's with 2hp can get you moving and keep you moving at a steady pace

--Phil
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Old 10-03-2010, 05:59 PM   #9 (permalink)
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120 yet?

You get near your goal with that thing yet?
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Old 10-03-2010, 10:26 PM   #10 (permalink)
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Quote:
Originally Posted by HaiRuiDe View Post
You get near your goal with that thing yet?
120mpg? Yup.

That's what it returned holding a steady 15mph on the flat. Spent a day riding it about, and filled it right up again, that's what it returned over the mileage (verified by driving my car the same route, about 40 miles).

Not bad for a pile of scrap

--Phil

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