I've had several of these engines years back and when they run they are great little guys. Well made, but fussy when it comes to the fuel pump. Let it sit without running for too long and they dry up. You may be able to get the parts through misamigo here on the forum... not sure, but a pm would probably answer the question. I still have one of these motors and have thought about mounting it on an elderly 3 speed Robin Hood made in England. Yes, it is about 26CCs. Bigger is not always better. Depends on what you want. For what it is, a motor assist for a pedal bike, I think it's perfect in that you can totally disengage the drive wheel and pedal without any drag at all. And on the flats it is enough to cruise along at moderate speed without pedaling. In other words it is a nice combination of getting some exercise and also sitting back for a quiet putt putt down the road. I used to make my own rollers for them out of epoxy in both a dry weather and rainy weather version. They can also be made from skate board wheels.
The question I've had in the back of my mind is if there is a way to bypass the fuel pump problem. Why does it need a fuel pump? The gas tank being lower than the engine is why (he says without really knowing), as it is affixed to the front wheel axle. Seems like a kind of rinky dink setup to me, making things more complicated than they need to be. I've also found that many of these stock Tanaka tanks tend to rust out after forty or fifty years and need cleaning out at the least and more likely repair. Around the same time period of the bike bug there was an American made friction drive motor of similar design made in Wisconsin called "Chicken Power". I forget the name of the manufacturer, but you can find it on the net. Try "Moped Army" and you can find pictures. Anyway, the reason I mention it is that it used a gas tank which mounted to the handlebars and was made from a tin can (rubber cement can) so that it was gravity feed. Making a similar tank is simple enough to do and I wonder if having the tank above the Tanaka motor could eliminate the need for the fuel pump. Or would it require a different carburetor? Or maybe the stock one could be modified. If so, then there would no longer be a problem with dried up fuel pump parts which are no longer available through Tanaka. Might be worth looking in to, eh?
For me this is kind of on the back burner with a lot ahead of it on the to do list. I don't understand why Tanaka stopped making this motor which first came into use prior to WWII. It was wildly popular in the states for some years and was sold under different branding... Free Spirit through Sears. I see two obstacles to returning old ones to service. The first is the drive wheels which can be home made. The second is the fuel delivery problem with the diaphragm. The little motor needs three things to run. Spark, air and gasoline. If it can be made to run by gravity feed these well made little motors will keep putting right along. One of these days I'll dig mine out for a look and also dig out my manuals (owners and parts list/diagram). If someone is willing to scan and post the manuals here on the forum (perhaps as a sticky) I'd be willing to send mine for sharing. I don't have a scanner.
Please post your progress/adventure here for mutual benefit. Thanks...
SB
I'll definitely be posting when I get working on it, and will share any info I come up with.