Topic: rpm differences

[vulture7]

Measured the individual rpm's with a digital tach on my cb750a. Found 1 and 4 cylinder at 900 rpm and 2 & 3 at 600rpm. Not sure what that could be? Carb sync???

Wayne (wisconsin)

[mlinder]

That's impossible.

Either instrument error, installation error, or you were running the bike at different speeds each time you measured.

[BobbyR]

That's impossible.

Either instrument error, installation error, or you were running the bike at different speeds each time you measured.

The reason it is impossible is that each piston can't run a different RPM than the other is that they are connected to a common crank.

[mlinder]

That's impossible.

Either instrument error, installation error, or you were running the bike at different speeds each time you measured.

The reason it is impossible is that each piston can't run a different RPM than the other is that they are connected to a common crank.

I think you mistyped can't

Sorry, fixed it, didn't want to confuse the issue any further, bobby.

[BobbyR]

That's impossible.

Either instrument error, installation error, or you were running the bike at different speeds each time you measured.

The reason it is impossible is that each piston can't run a different RPM than the other is that they are connected to a common crank.

I think you mistyped can't

Sorry, fixed it, didn't want to confuse the issue any further, bobby.

Thanks, and good ctach. The word is CAN'T. I revised the original post. We don't need to confuse people.

[vulture7]

No the bike was sitting there idling with no change in throttle position by me.

i have found the digital tach i have used to be very accurate when checking other multi-cyclinder bikes and comparing to the bike tach.

I understand that the pistons and crank are all connected.

I question if it may be an electrical or firing issue.

This tach clamps on to the plug lead.

Wayne (wisconsin)

[mlinder]

If that were the case, it'd have to be missing 1 in 3 fires. And it would have to be, like, every 3rd evenly, to fool your tach, unless that tach measures a whole minute of time before giving you an average RPM or something.