Fat rear tired commuter/MTB with FD, jackshaft and Weedeater

This is a bike I've owned for over 17 years, it originally started as a home market commuter that Nishiki sold in the US back in '87, the CitiSport, with alloy wheels, thumb shifter 5-speed, rack, chainguard and fenders.

I found it at the local dump-recycler for $5 with front fork, in near new shape. I got an idea in '97 to make it into a beach and firm sand riding bike for our local long beaches and trails to them through the local dunes. Never was really great at riding soft sand though.

It's been stored for a number of years since I made it. I've also wanted to make a motorized bicycle since the early 80's, and a plan came together to match this with an old Echo-SRM 302 weedeater I own, a 32 cc displacement 2 cycle from the early 80's. The engine is really old school with points and condensor and nice external finger knobs to adjust the low and high carb mixture circuits. Pictures..














It's already about 90% done. It's funny, but it being this close to finished I'm finding that the last 10% of the job is starting to be 70% of the trouble and fussy little details to fix and tune.

I'm presently tuning the friction drive and will need to purchase a Gates PolyFlex drive belt for the friction drive's pulley at the jackshaft to the engine pulley. Last week was spent getting the engine mounted to the reinforced rack I improved the strength of. In between all this, there's been a lot of little fiddly repairs and improvements as the build has progressed from late May. I haven't been keeping a great record of all the stuff I've done, suffice to say the bike has had a near overhaul, as had the engine.

Cheers, watch this space..

Couple more images from last week, I've finished the throttle connection and got the friction drum/jackshaft-pulley mounted to the seat tube.

Some progress, although it's going to be a while before I'm riding it with engine power my Ebay order is being held up for some reason.

A few notes about this bike The Kioritz-SRM engine, 32 cc, is an old school Japanese industrial weedeater with auto clutch, unfortunately it's clutch is unlike the present 74mm clutches so prevalent in MAB kits. So I had to fabricate my own drive.

The seat-tube clamp is from the handlebar mount for the weedeater. Loosen the 2 clamp bolts and slide it up and down the seat-tube to engage the tire with the friction drum. This also loosens the belt tension which should extend it's life some.

The friction drive is a 4.3:1 reduction with a 5 mm Polyflex belt, the friction drum is a 2-7/8ths" diameter hole-saw with a random stick welding spattering on it's outside of Nickle Chromium surface hardening welding rod for the friction 'roughness'.

Probably won't be an issue as the rear tire is from a 21" street wheel from a bagger Harley, and is used. It still has lots of material between it and the inner tube.

The 21" rim is from a 1980's Honda XL something, which I laced it myself to the rear hub. The rear hub is widened along with the rear frame seat and chainstays to accommodate the widened tire. It's not exactly a light set-up, this bike was built back when fatty tires and rims for MTB's were not available.

I'm on a budget for this build, so I've D.I.Y.'d a lot of this bike's parts.

I wanted to update this thread but then noticed that my image links aren't working any more. :?:

There has been some changes with this bike, I'm now running a different engine and better drive pulley off the engine, and it's been working quite well. I should have some images soon of what work I've done when I get time.

OK here's what I've done recently with the DIY Citisport..

New engine is a McCullough ProScaperII 30 cc with reed induction, it comes into it's power-band at a lower RPM, and overall runs much better than the Echo. I'm really happy with it.

I scrapped the fat-tire motorcycle rim/tire because of an insurmountable out of roundness issue, in favor of a old RM25 Araya 26" rim with a Specialized 2.5 folder street-tire. I've laced up the rim and new tire/tube myself.

I am a bike mechanic..

The new belt pulley on the ProscaperII was made by a friend with a metal shop and required no modifications to the new setup other than some new holes in the rack to mount the other engine onto.











What I'm discovering is that with this engine is that I'm going fast enough to keep up with traffic in urban conditions. I'm also thinking an RST suspension fork may be in my future, along with a front fender and wireless cyclometer.

wheelbender6 said:

Three things I like about your build, Citi-sporter;
1 - Its DIY
2 - Your Nishiki has an old school lugged frame
3 - The belt driven roller

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Why thank you Wheelbender6!

You'll also notice the extended range fuel tank from Ace hardware and the thinwall Tygon 3/16" fuel-line and it's ( hidden) clunk from a local saw repair place.

The other thing I like is the friction drive is relatively low friction, I can slow down at the top of a moderate downhill slope, let the engine idle and pedal enough to get up to about 10 mph and when it hits the slope it will coast down at quite a clip. I've had to use my brakes on the down-hill part of the steep grade North of Bandon, it's like driving a 2 cycle SAAB car with the free-wheel transmission, whizzing along with the engine behind me happily idling away.

Those are the bits I really appreciate, and that the engine and other parts were nearly free.

I'm not sure about the fuel range but, I have ridden this bike a good distance already, did my commute to work, roughly 68 miles round-trip. with a little 12 oz tank, and had to refill it twice going both directions ( 4 times in all..) I think I'm getting roughly a little over ten or 12 miles per 8 oz. of fuel, so the mileage isn't bad, it's 'geared' for easier hill climbing. It will tackle the 6~7% grade north of Randolph road on Hwy 101, North of Bandon, OR with the engine laboring a little, probably down to about 14 mph, feels like it's comfortable cruise speed is about 18~22 mph.

Lots of little issues that still need attention but it's very close to being a daily rider.

Gotta show Augie this someday.

Ludwig II said:

How good is that large diameter roller in wet conditions? I'd assume it's got to be better than something about 1" diameter.

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Well we're sort of having a drought right now, hasn't been any appreciable rain since July. But we lately get marine fog/mist, but I haven't had it out in it yet.

I suspect it will slip if coaxed.

I ride this as gently as I can, because the clutch bits are metal/metal and I want them to last. The tire roller interface will slip before the clutch will, I'm guessing.

I have the roller in about an 1/8~3/16" depressed contact, and the tire/roller patch is pretty large, just not a lot of pressure. Probably why it rolls so freely downhill.

Yeah that seems like a crude way to do it. I was wanting to use the rack mount to take advantage of a more centralized C/G engine mass with the drive roller and bits mounted to something with a lot of strength. The fact that the Gates Polyflex belts work great under these conditions and power levels is heartening. There's no appreciable wear on the belt "V" faces or fraying of the Kevlar belting. The pulley's get a little warm. I have to watch the belt tension and tire inflation. It seems like a real slow leak in the rear tire tube, kind of bugs me a little because it's a new tire/tube, both are Specialized and I'd expect better life.

The 26X2.5 Compound folder is doing OK, it's a lovely smooth rolling tire with perfect concentricity and no problems with bead seating. Glad I didn't buy the Bell ones.