Topic: CB350 wasted spark....working

[adams77]

I am in the midst of bringing a 71 CB350 back to life when I had an "Oh Crap" moment.  The plug wire pulled out of the coil.

After a few cuss words and slinging the 10mm wrench across the shop I saw the solution.  I had an old 750 coil and it has two outputs.  So I wired both condensors together to the single coil and viola.....Im running again.

Anyone else done this?  The only down side is the wasted spark during the exhaust stroke but I can live with that.

[mlinder]

Do you mean you are running one coil for both plugs?
If so, remember that the cb350t is a 180 degree crank, not a 360.
There's more going on than just a wasted spark on the bottom of the exhaust stroke.
The coil has 1/4 the time to recharge between firing (well, kinda, between 2 of the firings, anyway), and is splitting the power to spark plug in half every time it fires.
You have anotehr 750 coil? Becasue you could just wire that up with properspark timing and leave one of the plug wires alone on each.

[Sam Green Racing]

I'm not sure Mark, don't the CB350s points run off the cam which is half the engine speed.

Sam.

[mlinder]

I'm not sure Mark, don't the CB350s points run off the cam which is half the engine speed.

Sam.

Yep, but the single coil still has 1/4 the time to charge between spark 1 and 2 that they had previously.

Each coil, originally, had 2 revolutions in which to recharge themselves.
With this setup, with 180 degree crank, it has 1/2 revolution between discharging on 1st and 2nd firing, as cyl 2 fires only 180 degrees after 1 fires. Thus, 1 and 2 fire, 1 goes 180 degrees, and then 2 needs fire, and it fires on 1 again at the same time.

[adams77]

This coil was on a bike that had no problem turning in the teens (thousands), I dont think the little 350 will ever see much of that.  I am going to run it and will post up results.

[mlinder]

Don't get me wrong. It's a creative solution to your problem.
Now I understand what Sam was getting at, though. With the cb750's points on the crankshaft, it's spinning same as engine speed, whereas the cb350t's is running half engine speed. My concerns were that the coil has 1/4 the time for recharge as the stock coils on the cb350, however, it's only 1/2 time as on the cb750.
So, the charge time for the single coil on the cb350 at 5 grand  is the same as the 750 at  10 grand.
However, with the 10 grand redline of the cb350, I dunno how well it will do way up there.
Have fun and let us know how it goes.