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Old 05-29-2012, 05:44 PM
TheOtherChris TheOtherChris is offline
Motorized Bicycle Member
Join Date: Apr 2012
Location: SE Idaho
Posts: 47
Default Straight Bar for first build

After lurking for quite a while, I decided it was time to come out of the closet.

First, let me tell you up front that I am "an old fart".
Years ago, I found a running Schwinn straight bar bike at a thrift shop for $15. My wife and kids were excited that I was finally going to "get some exercise". (Yeah, right)
The rims are bent pretty well and that front sprocket is way bigger than anything I want to peddle, so I quietly started to plan a MB.

This year I ordered a HT engine from (can't remember). The engine arrived quickly. It is a 66/80cc slant head with adjustable NT carb.
As this old bike is not a V-frame, I had to mill up a new front mount for the engine in order to allow it to clear that big front crank sprocket.

Then when I went to mount the new rear sprocket from the kit, I discovered that it would not fit over the Schwinn/Bendix coaster brake hub.
So, I mounted it in the lathe.

Who knew a camera's eyes could be as bad as mine.

After turning out the center, the sprocket mounted up to the rear wheel just fine.

Since this bike has been out of service for years, I figured I should take a look at the hubs. Good thing too. The grease had the texture of clay, so I cleaned and repacked the bearings.
I broke that cheap spark plug boot and replaced it with an NGK one.

When I finally got everything up and running, I headed down the street. (Yes, I used the recommended gas/oil mix for the first tank).

The bike made it about 30 seconds and seized up. Further inspection indicated crank bearings had failed.
I emailed the seller and they agreed to take the engine back. They sent me another and it had a completely different set of problems.
The head did not seal down against the cylinder. There was no room left to tighten them down, so I figured I would pull them and add a washer or two.
As I began to loosen them, I realized the entire stud was turning out.
Closer inspection revealed the acorn nuts on the head are NOT meant for these studs. Each had been forced on about 2 turns. I pulled them all and added two washers and bolted everything back in place. (I will replace the studs and nuts at a later date).

Wouldn't idle for crap, so I added an O-ring to the end of the intake tube and that took care of it.

First tank of fuel GPS'd a speed of only 22mph.
Now, I know I mentioned I was old, but I am also a 220 pound couch potato attempting to run this bike at an elevation of about 4800' above sea level??

After 30 miles of break-in, I thought the float was sticking as fuel was pouring out of the carb. got it home and tore the carb apart and found a small piece of white plastic (probably from that cheap inline filter) stuck. Cleaned everything out and added a good inline filter. When I got to the second gallon of fuel, I decided to port match the intake and exhaust and begin to adjust the air/fuel mixture. With the extended NGK plug I am running, the engine currently likes the second notch from the top on the needle.

I now GPS 26mph with the stock 44T sprocket and still on the second gallon of fuel.

I did this mostly on a whim and have learned that I LIKE motorized bicycles.
I am now planning to replace the bent rims with something better and lace in a drum hub for the front. I also want to get an in frame tank from sportscarpat and repaint for a more classic look.

But I can see things like shift kits, 4-strokes and more bikes in my future.
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