BSA Lightning Bobber


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Check the number of teeth. IIRC they use a "hunting tooth" so that the gears don't wear out unevenly. There's one more tooth that there should be on one wheel and that way they move relative to one another but because the diameters are the same, they stay in synch but the marks "move".

Now I could be completely wrong with that. I am trying to remember something I haven't had to think about for decades. And I sold all my T120 stuff a very long time ago, so I don't even have the manuals to check.


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I noticed that whenever I kicked the engine through I would feel a slight puff of air coming back through the carburetor so I started to wonder if the cam timing was off. I wanted to get a look at the kickstart quadrant shaft anyways so I decided to remove the inner timing cover. I turned the engine through a bunch of times and never got the timing marks to line up so I removed the idler gear and line things up. I think I’ve got it pretty much the way the picture in the manual shows it.

How did it get this way to begin with? We may never know. Fairly certain that the PO told a few lies when he said that he had been riding it though. I don’t see any evidence that it jumped time. More to follow when I get time. View attachment 234041

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Mines the same

But once you set it up properly it could take a million spins for the timing marks to line up properly again

The other side was not so pretty

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Over 1,000 Posts
Just got a new kickstart quadrant in the mail. New kickstart ratchet pinion and the timing box gasket should be here this week. Hopefully I can get it put back together and see what happens.


Over 1,000 Posts
Installed the new quadrant and new ratchet pinion. Put the timing cover back on and finally got the kick lever to install smoothly. Shot a little starting fluid in the carbs and gave it a kick. She lit right off!
Now just to get some fresh gas in the tank and see if she will run on that. I made a video of it firing up but can't upload it for some reason.


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Great news!!!
Upload vid to YouTube then post the link.
I think I’ve had trouble here, if video is more than just a few seconds long.


Over 1,000 Posts
Wow, been a long time since I updated this. Still working on it when I get a chance. Garage time is few and far between with a little one in the house. I also lose a lot of motivation to go out to the garage when it's frigid.

My tank was pretty crusty inside and the petcocks were pretty well shot. I ordered some new petcocks and let some vinegar soak in the tank for a while. It's not as clean as I would like but it's enough I'm not too worried about fouling the carbs for now.
I was troubleshooting the bike without a key switch and a battery siting on the floor, just connected enough to power the ignition. I got a new key switch and connected things up properly. I will still need to make it pretty later on but I can at least start and work on the bike now.
I can get the bike started but the carbs definitely need some tuning. At first it would only run on one cylinder but I think I figured out that the left carb needle was stuck. Now it'll run on both cylinders but idles very high. Next garage day I'll try sorting that out.

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