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Old 1 Week Ago
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Default F40 3 cylinder sparks per revolution

I'd like to add a tach to a 13ft Whaler I'm restoring and I'm installing a 2001 F40TLRZ 3 cylinder. I don't want a standard tach because of the hole in the dash so I'm looking at a Tiny Tach or from ENM model PT18 which can be mounted without a hole. Both are programmable but you need to know the sparks per revolution for the engine. I've searched high and low but can't find the info for this engine.
ENM shows a 3 cylinder 4 stroke engine has 3 sparks per 2 revolutions but is that true for a Yamaha outboard? I've read that some engines have a "wasted spark"
Can anyone provide a specific answer on how many sparks/revolution for this engine?
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Old 1 Week Ago
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Do you need to know before placing the order or for some sort of setting on the tach itself?
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I want to be sure I order the right unit, so I would like the info prior to ordering. Thanks
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3 cylinder 4 strokes have a crank angle of 120 degrees so must be 3 sparks for every 2 revolutions unless a wasted spark system is used but this is difficult to imagine as no pistons are at the top or bottom of their stroke simultaneously. If the engine has 3 separate coils then it must be 3 sparks per 2 revs...

Last edited by cleddau1; 1 Week Ago at 03:36 PM.
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Old 1 Week Ago
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The retailer doesn't know what unit is designed to fit your engine??

Can you post a link to the seller please...

I would think the unit has a switch to convert from two stroke to four stroke...

If your engine has a wasted spark, it would put out the # of spark as a TWO STROKE. (Dunno if that helps).
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A three cylinder four stroke having three coils will not use a wasted spark ignition system.
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where do you plan on mounting this tach so you can see it while running the boat, the PT18 only has a 5 foot lead for spark pick up signal.


Also it is programmable to 3 per rev or 3 per 2 revs along with many other configurations, so I do not see where it would matter when buying for any 2 or 4 stroke

Last edited by 99yam40; 1 Week Ago at 10:49 AM.
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Old 1 Week Ago
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Thanks for the replies.

The motor does have one coil per spark plug, so it sounds like that means 2 sparks/2 revolutions - is that correct?

Here's a link to the tach/hour meter I'm thinking of using:

http://www.enmco.com/pdf/707.PDF

It would be mounted on the "dash" of the console using velcro. True about the five foot lead but it can be extended with the same or heavier gauge shielded wire. I only need another 4 ft for the whaler.
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One coil per plug in a four stroke would mean one spark for every two revolutions.

Piston comes to top on compression stroke, plug fires. Piston goes down and then back to the top on the exhaust stroke. Plug does not fire. Piston goes down then back to the top on the next compression stroke, plug fires.

In a wasted spark configuration the plug would also fire when the piston is at the top of the exhaust stroke. The plug firing does nothing at that point. That is why it is referred to as a "wasted" spark.
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Quote:
Originally Posted by ollie366 View Post
Thanks for the replies.

The motor does have one coil per spark plug, so it sounds like that means 2 sparks/2 revolutions - is that correct?

Here's a link to the tach/hour meter I'm thinking of using:

http://www.enmco.com/pdf/707.PDF

It would be mounted on the "dash" of the console using velcro. True about the five foot lead but it can be extended with the same or heavier gauge shielded wire. I only need another 4 ft for the whaler.
The linked literature is confusing to me. The tachometer connects to but one cylinder. All that needs to be known is if the motor is a four stroke and fires every cycle (wasted spark) or every other cycle (conventional). Number of cylinders should be irrelevant. Whatever RPM one cylinder is running the others will also be running.
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Old 1 Week Ago
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Strange I was not even thinking about it only monitoring one spark plug wire, but you are correct.
I was thinking more like coil wire on old distributors on automotive stuff.


Also to the OP I have seen the induction of the other plug wires under the cowling confusing the cheap little tachs.
you would be better off using the proper outboard tach
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Old 1 Week Ago
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Quote:
Originally Posted by ollie366 View Post
Thanks for the replies.

The motor does have one coil per spark plug, so it sounds like that means 2 sparks/2 revolutions - is that correct?

Here's a link to the tach/hour meter I'm thinking of using:

http://www.enmco.com/pdf/707.PDF

It would be mounted on the "dash" of the console using velcro. True about the five foot lead but it can be extended with the same or heavier gauge shielded wire. I only need another 4 ft for the whaler.
It says on the bottom of that PDF what the setting would be for your configuration. 4 stroke, 3 cylinder

There's only ONE unit you can buy...



*Not related but the BOLD feature does not seem to be working for me..
Anyone else?
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Old 1 Week Ago
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Test test test.
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Old 1 Week Ago
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Quote:
Originally Posted by TownsendsFJR1300 View Post
It says on the bottom of that PDF what the setting would be for your configuration. 4 stroke, 3 cylinder

There's only ONE unit you can buy...



*Not related but the BOLD feature does not seem to be working for me..
Anyone else?
works for me too.
must be that attack you had.
reboot to see if that helps
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Old 1 Week Ago
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Thanks guys.

I can "bold" on other forums, just not here (noticed it today) for some reason.

The "Smilies" (to the right) doesn't work either???

I'll PM admin, see if they can re-set. They usually answer within a day or two...
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