1972 CB175 Static Timing - 360 Degrees Good! Another 360 Degrees Advanced

[1sttimer]

Hey there! I'm working on a '72 CB175 and have a quick static timing question. It's a 2-cylinder but my points plate has only one contact, which tells me, I assume that the spark plugs fire every rotation of the crank shaft and both spark plugs fire every rotation. Only one cylinder would be on the power stroke at a time I believe, even though the cylinders rise and fall simultaneously (other would be on "blow").

When setting the static timing, I found that one one rotation of the crank, the timing light would go illuminate exactly when the "F" mark lined up with the indicator. Good news! However, on the next rotation, the timing light goes off a few degrees too early. When I come back around 360, it's right on the money and it rotates back and forth like this. Because there's only one point contact, do I just adjust the points so that it splits the difference between the two rotations, which would average out to both firing incidents being a little advanced? Or do I keep it like it is - one rotation spot on and the other slightly advanced? I can't adjust one without compromising the other right? Should I adopt an "if it aint broke, don't fix it" mentality?

Photo of the points plate:

Photo of how far advanced one rotation is. The other rotation is spot on.

 

[teazer]

The answer is YES.

It is what's known as Wasted Spark with one coil and one set of points. Works well. That timing is probably close enough for everyday running as it is. You could split the difference or leave it as it is, and I doubt there would be any difference to performance or reliability.

Q: does your points cam have two lobes or one? If it has two then the issue is that the second lobe is slightly advanced and could be ground down slightly on the lift side to equal out the timing. Use a sharpening stone - not a power tool to just flatten off the ramp a touch. Or leave it as it is and just run it.

Or replace it with an electronic ignition (Dyna etc) from a CB450 or GL1000.

For a low cost street bike, it would just run it as it is...

 

[1sttimer]

The answer is YES.

It is what's known as Wasted Spark with one coil and one set of points. Works well. That timing is probably close enough for everyday running as it is. You could split the difference or leave it as it is, and I doubt there would be any difference to performance or reliability.

Q: does your points cam have two lobes or one? If it has two then the issue is that the second lobe is slightly advanced and could be ground down slightly on the lift side to equal out the timing. Use a sharpening stone - not a power tool to just flatten off the ramp a touch. Or leave it as it is and just run it.

Or replace it with an electronic ignition (Dyna etc) from a CB450 or GL1000.

For a low cost street bike, it would just run it as it is...

Hey Teazer! Good talking to you again! Been a few years, yea? Hope alls well!

This actually isn’t even my bike - just trying to dial it in for someone else, and yeah it’s just a back and forth around town bike.

To your question, it has 2 very soft lobes on the cam. I have a sharpening stone in the garage! I’m going to give that a try just to say I’ve done it, ha. Thanks for the reassurance that everything should be fine regardless.


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[teazer]

No worries mate

 

[pidjones]

I may have to do similar on one of my GL1000s. I think that it is because the cam lobes cause the shaft to be off-center when turning by hand. I just wonder if the oil wedge in the cam journals centers it up when running? I have as much as a 4 degree difference on my 3/4 cylinder timing (when static timed, still need to put the strobe on it).

 

[1sttimer]

I may have to do similar on one of my GL1000s. I think that it is because the cam lobes cause the shaft to be off-center when turning by hand. I just wonder if the oil wedge in the cam journals centers it up when running? I have as much as a 4 degree difference on my 3/4 cylinder timing (when static timed, still need to put the strobe on it).

Interesting thought on the oil wedge.


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[pidjones]

Checked it with light at idle and 2500RPM, and they were in sync again. So, it appears that the oil wedge in the cam bearings does make a rather large difference.