Reading 2-stroke rpm with multimeter?

[phralh]

Did some reading on the web and found an article on how to read rpm's with a "car"-multimeter with rpm function. I was thinking of trying this on my '75 evinrude 9.9. As I understood the article, you hook up one cable to stopswitch cable (leads to breakerpoint) and the other to ground. Of course most meters are made for 4-stroke engines, but results can be recalculated to correct reading.

To recalculate a 1cyl 2-stroke - select 2cyl 4-stroke setting
To recalculate a 2cyl 2-stroke - select 4cyl 4-stroke setting

Am I doing the math correctly? Would this work?

Thanks
//Fredrik

 

[Sea18Horse]

Re: Reading 2-stroke rpm with multimeter?

For either a one or two cylinder 2stroke you would want to use the two cylinder 4stroke setting.

Both the one and two cylinder 2strokes fire each points once per revolution. And the four cylinder 4stroke would fire the points twice per revolution. So that wouldn't work. But the two cylinder 4stroke would fire the points once per revolution. Of course you could divide the reading in half if four cylinder 4stroke is all your meter had.

This gives me an idea. I had thought to get a tinytach to see what the rpms are running on my old johnsons. But come to think of it I think I have an old meter around with a clamp on (the spark plug wire) tach. pickup. I'll have to see if I can find that and see what kinds of settings it has. Hmmmmm, thanks for the idea.

Cheers....................Todd

 

[Sea18Horse]

Re: Reading 2-stroke rpm with multimeter?

Oops! Didn't see that this was a duplicate. :redface:
Already covered I see.

Cheers............Todd

 

[fix_it]

Re: Reading 2-stroke rpm with multimeter?

The clamp on meters that hook to the spark plug don't care how many cylinders there are. One cylinder of an 8 cyl engine will fire the same # of times per revolution as one cyl of a 1 cyl engine. There will be one pulse per rev for a two-cycle and one pulse per two revs for a four-cycle. Therefore, if the clamp on meter doesn't have a two-cycle setting, just divide the reading by 2.

 

[Sea18Horse]

Re: Reading 2-stroke rpm with multimeter?

The clamp on meters that hook to the spark plug don't care how many cylinders there are. One cylinder of an 8 cyl engine will fire the same # of times per revolution as one cyl of a 1 cyl engine. There will be one pulse per rev for a two-cycle and one pulse per two revs for a four-cycle. Therefore, if the clamp on meter doesn't have a two-cycle setting, just divide the reading by 2.

Exactly! I haven't looked at that particular meter in years. In fact I don't even remember exactly where it is :redface: . I don't remember now whether it had a 2stroke setting or not. I'm thinking not. So as you say I'd need to divide by 2. Thanks!

Cheers.............Todd