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Chapter XII: False Start #3 – Runaway!



I had finally reached a point where I could fire the girl up.  It had been a few years since I kicked over something with such high compression that was this tall, so the bike went on the stand.

Fluids…check.  Oiled filter…check.  No visible leaks…check.  Spark at the plug…check.  Time for the moment of glory.

First kick…nothing.  Second kick…a burble…YES!  Third kick…

…and a nightmare began to unfold in my garage…

There are many younger riders, or mechanics from the four-stroke era, who have never experience what I am about to describe but believe me when I say this is all real.

 On that third kick, the bike revved up on that natural blip you give when kicking a bike for some reason.  Unfortunately, it kept revving…and revving…and revving.

Before I had time to think, the bike was at a mechanical rev-max.

The throttle was down.  Was the carb stuck? No.  Almost breaking my thumb on the kill switch…nothing.  Did I mis-wire it? 

It was time for drastic measures.  I pulled the spark plug cap, taking a few shocks as I did it…and nothing changed.

At that point I knew I had an air-leak-induced, ultra-lean runaway.  Some readers will want to throw the BS-card on that, but in an ultra-lean condition, the spark plug (or a carbon deposit in a worn engine) can super-heat to the point of supporting ignition like a diesel, so pulling the ignition wouldn’t help.

With an older, less compact bike, I’d reach in and put my palm over the carb mouth, but there was no way to do that here.  I also didn’t want to slam the bike into gear on a stand when the bike was beyond what I would have though of as a “redline.”

I shut off the fuel, waited for the carb to run dry, and prayed I wouldn’t get hit by flying parts from a motor-grenade.

The bike finally stopped.  Nervously, I slowly kicked the bike through and sighed a shaky sigh of relief.  The bike hadn’t seized.  I joked to myself about break-in.  So much for a three-heat-cycle intro on this new top-end.  It just got three hours of wear in about 90 seconds.

Once the bike cooled down, and my adrenaline spike passed, I assessed the data I could gather.  There was quite a bit of smoke in the garage and of course the bike didn’t seize.  Perhaps there was lots of old premix down in the crank cavity?  That air leak had to be somewhere, and it was likely somewhere I touched.

I trusted the level of the base and head decks for the recently-serviced cylinder, as well as the recently-cut head.  The gaskets at those points were good, and all torque settings were right.  Then I found it.  The bottom center bolt holding the rubber manifold to the reed block was loose.  The air leak had come in past the reed block. 

Not torquing the bolt was my fault, but I also didn’t like the two-piece setup of the manifold and the reed block assembly, with the two gaskets needed.  I decided on that alone to eventually replace that intake tract with a one-piece Boyesen Rad Valve whenever I replaced the carb.

I re-drained the oil and got another “hairy” drain magnet and glittery drain pan.  At least this allowed a good trans flush.

Nervously, I checked everything out again…fresh oil.  Good coolant level.  No leaks.  Everything torqued properly.  Fresh plug, just in case the insulator had cracked or the electrode was compromised by that heat.

I kicked again…feeling a little less compression (figured it was just break-in).  On the second kick, the bike started up with a normal idle and responded to very timid/ginger throttle applications.  The bike and I had dodged a bullet, and we were both ready for the next step.


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