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Premium Member
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617 Posts
Discussion Starter #1
Last night I installed the new breaker points that came in the mail. I static timed the engine using a speedo light using tbpmusic's timing thread. Then I ran the bike with a timing light hooked up so I could test it at idle as well as at advance. Timing is now bang on and my pitted points are sitting in a box as spares.
I also checked the condensers according to the service manual where you hook them up in line with a battery and a light bulb. They 'passed the test' by not allowing the light to turn on. Sort of an uncomplete test if you ask me to determine if they're working or not ;) My valves are set. My coils pass an electrical test both when the bike is cold and when it's hot. I've nipped about 1/2" off of the plug wires and sprayed contact cleaner inside of them and reinstalled the resistor caps. Compression tests out on a warm engine at ~170psi in both cylinders. The carburetors are completely (meticulously) rebuilt.

But... It's still missing at about 6krpm. My only thoughts are that the coils are just old and crusty, in particular the plug wires. I caught it arcing out of the wire insulation to my clutch cable once and put a bunch of electrical tape on it to make a barrier.

My spark plugs look great. Just like you'd want them to on something not running rich or lean.

Thoughts?

The only other thing on my radar is that the on/off switch on the right handlebar almost works too well. In the 'on' position the bike is easy to start and runs. But when you want to kill the engine, it BARELY takes any bumping of the switch either way to either 'off' position to almost immediately kill the bike. It's almost as if my connection to keep the coils powered up could possibly be weak.
 

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Sensei
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27,161 Posts
Sounds like you are leaning out at high revs...... what type aircleaners and pipes do you have?.....
 

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Premium Member
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617 Posts
Discussion Starter #3
Stock air boxes with these filters:



They still seem to have little enough restriction to use.

The pipes are half-gutted OEM from a 71 CB350.

Don't know if you can see it here:

http://farm5.static.flickr.com/4048/463 ... 57a6_b.jpg

But it looks like they've pulled the baffles out but left the rear stopper there. There's about a silver dollar sized hole in the back of both of them that lets out exhaust.

I ran straight pipes last sunday (just because it was convenient to make a set up quickly) and the straight pipes are about 10x louder than these. These are loud, but not to the point that there's no backpressure.

The jets are stock. And I'm at 1000 ft above sea level. I figured it'd be in the safe range. The engine smells pretty good now with the new points installed. Not running hot, or it doesn't seem so.

So do you think maybe if I run it down the highway until it starts cutting out I can kill the engine, coast to a stop, and get a lean reading on the spark plug? (gray or white-ish looking)
 

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Sensei
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27,161 Posts
That would be the appropriate test.........
 

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Premium Member
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617 Posts
Discussion Starter #5
Here's the result of killing the engine at 7krpm while it had been cutting out on me and coasting to a stop.

The left pipe is a bit 'more gutted' than the right one. Both are devoid of baffling material, but may have baffles installed in them. Someone pulled stuff out from the rear outlet at some point.

The left side plug reveals itself to be a bit leaner too. However, it's the right cylinder that cuts out.

Left plug:



Right plug:



The left plug looks maybe a bit leaner than I'd like at WOT, but it doesn't look dangerously lean to me. The electrode has gone to white, but the tip is still brown rather than gray or white crusty.

Perhaps it's the ignition coils, the coil wires, a weak ignition circuit connection (handlebar switch), or the mismatch in the exhaust pipe conditions throws the cylinders out of balance?
 
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