Tach question - 68 merc 500

[akwormy]

I want to work on idle and timing issues but have no RPM info since this is a tiller steer motor with no tach or controls wiring.

There is a sticker on the front of the motor that says only use a certain kind of tach (sorry I'm not by the motor right now) and of course there is no tach with the motor, but I have a digital multimeter with a tach function - will this work?

If so then, what wire on the switchbox would I connect it to? (I think it's got blue, orange, and one other)

Thanks!

PS - I'm confused by the types of ignitions on these things. Mine says thunderbolt on the cowl and on the distributor it says lighting energizer. I keep seeing these two terms used on the forum like I have one or the other...

 

[Steven1962]

Re: Tach question - 68 merc 500

You have a type II Ignition system, these motors have 5 diffrent types of Thunderbolt Ignitions I II III IV & V .. Yours is called a ADI
" Alternator driven Ignition" has a distributor w/two coils one for low speed one for high speed.

I do not know where to connect the tach on this motor but hopefully someone here can help you.

 

[akwormy]

Re: Tach question - 68 merc 500

wow - it's worse than I thought!!! (five types???)

So the distributor - is actually the driver (aka the magneto). Starting to make sense now. Does it actually have points to adjust like a distributor?

Saying mine is a type II does it matter that I only have one coil? (maybe the two part coil is all contained in one housing...but I only see one coil wire going to one coil)

thanks for the info - hopefully someone can tell me where to hook up a tach and also what if anything this tach warning about only using a certain kind of tach means.

cheers

 

[Droll]

Re: Tach question - 68 merc 500

Does your engine got El start or just the pull start ??

Engines with electric start got a charging stator under the flywheel, any modern outboard tach can be connected
( might require you to move one wire on the engine ( from the switch box to the AC side of the rectifier ))
An engine with electric start would use the Thunderbolt ignition ( uses current from the battery to make the spark ).

Engines with only the pull start doesn't have any charging stator under the flywheel, they also uses the Lighting energizer ignition ( this unit makes it's own power )

A picture of the distributor will tell us what you do have .
And since it's a 1968 model.....some previous owner might have done some modifications.......

An easier tach would be a Tinytach , TT226NR-2C should work fine ( easy install.... wrap a wire around #1 plugwire. )
Should work on ALL 2-stroke engines.

Yours is called a ADI
" Alternator driven Ignition" has a distributor w/two coils one for low speed one for high speed.

Wrog...ADI "Alternator driven Ignition" came on later models, does NOT use a distributor.
This system got it's power from the stator ( self supported ), it also had a ignition pickup under the flywheel, got a switch box on starboard side + 4 coils ( one for each cylinder ).

I think the ADI system was first used on the 1976 Merc500.....

Arne Kjetil

 

[Laddies]

Re: Tach question - 68 merc 500

That engine is battery CD and you need a induction tach or one that runs from the alternator. Arne is right ADI ign was not built till the mid 70s.

 

[akwormy]

Re: Tach question - 68 merc 500

it's a pull start - so need an induction tach. Understood.

I'll start searching for one cheap...any tips for finding one feel free to share. The tiny tach might be the way I go. Thanks

 

[Laddies]

Re: Tach question - 68 merc 500

If it's a 68 pull start it probably is magneto ign. It would have a single wire attached to the mag to ground it out Mercury didn't build may of the mag engines in 68 but it sounds like you have one. With a mag you can use a Tiny Tach or any tach that is adjustable for a 4 cyl 2 cycle engine.