Timing light and Tachometer

[tony7914]

Hello again!
I need your advice once more, my bike is back together with no problems I want to double check the timing now. Can you recommend a timing light and a tachometer that will work on my bike that I can get from someplace like auto zone or advanced auto?

The book is clear on the timing procedure but it doesn't tell me where to hook the tach to, can you help on that one too please?

Thanks again!!

[John]

Timig light connections

The battery leads on the timing light connect to the battery, and the pick up clips over the #1 plug wire. There will probably be some instructions come with the light.

[tony7914]

Thanks,
I know where to hook up the timing light, what I need to know is what kind of tachometer to buy and where it gets hooked up, the book recommends not using the bikes tach but doesn't tell me where to hook one up or what kind works with it.

[John]

Most quality timing lights have a built in tach already, so no need for an external one.

[tony7914]

Originally posted by John
Most quality timing lights have a built in tach already, so no need for an external one.

Do they hook up differently? Could you recommend a brand or model that would work for me?
Thanks again!

[Dennyz]

The biggest problem with aftermarket tachs, is the XS has two coils for 4 cylinders. Either the tach has to be able to work for a 2 cylinder engine or you have to build a small circuit to "OR" the two trigger pulses together.

[pggg]

Hey tony ignore the books 'aother tach' B.S. coz the bikes' tach is perfectly O.K. for setting the timing

[Pat Kelly]

When using a diagnostic tach (such as on some timing lights) just divide the RPM readout in half.

[trbig]

OK.. maybe I'm showing my ignorance, but why would you divide it by 2? Wouldn't it be X 2? The piston would be making 2 rev's per spark, correct? One compression stroke, one exhaust stroke. If you are just attaching it around the number one plug wire, the other coil wouldn't come into play would it?
Come to think of it, does a car timing light already do this math for you? It should only be sparking every other stroke also?? OK.. now I am confused.... but nuttin new to me!

Tod

[randy]

Tod,

We have what know as a 'wasted spark' system. When the coil fires, one cylinder is on the power stroke and the other is on the exhaust stroke, 180 degrees out of phase with each other.

You divide by two because the plug fires twice per cycle for each cylinder.

[trbig]

Well... then it would seem that you wouldn't do anything. What you see should be what you get. The plug is firing on each revolution. Aren't you determining on an RPM, how many times per minute the motor is spinning? Even though you only get 1 power stroke and one exhaust stroke per "cycle", that is 2 revolutions. Counting each spark would be the correct rpm wouldn't it? An rpm isn't the amount of "cycles" per minute is it?

Tod

[tony7914]

Hi,
I picked up an Actron CP7525 timing light with digital tach in it today and I'm going to try it out. Thanks again folks.

[randy]

Tod,

Think of a one-cylinder engine. You get one spark for every TWO revolutions of the crank.

Now consider two one-cylinder engines tied together, and the coil is firing both at the same time, only one of them is on the power stroke. As the pistons come round again, the other is on the power stroke. So you get TWO sparks for every revolution of the crank.

Divide by two

[trbig]

LOL.. Still not getting it. You have the piston coming up for compression... *Spark*... one revolution. Piston coming up for exhaust stoke... no power, but still a *spark*... 2 revolutions. So... 2 sparks... 2 revolutions.
Each time the piston goes up, the crank has come around... whether it's a power stroke or an exhaust stroke... still a revolution. Each complete "cycle" of an exhaust and compression stroke would be 2 revolutions. 1,000 of these "cycles" in a minute would equal 2,000 rpms. I guess I am just missing something.


Tod

[randy]

Right. Now, since you have TWO cyclinders on the same crank you have twice as many sparks.

Divide by two