25 2 stroke idle rpm range / tiny tach

Just hooked up the tiny tach to my new merc sea pro.
There are 2 cylinders on this motor just for reference. Max RPM per the manual are 5000-6000
Idle RPM is not specified in the manual so not sure what I should be expecting.

At first the tach was set at 360 degrees which = 1 spark per revolution. The wire was hooked up to the bottom spark plug wire. Idle rpm read 4000 - 4100rpms with the ear muffs hooked up on the hose.

Reset tiny tach to 180 degrees which = 2 sparks per revolution. Wrapped once around both spark plug wires, per the technicians reccomendation at tiny tach. Idle reads 1860 -1900 rpms.

Still seems like a high reading for idle.

Any ideas or experience on how low should I set the tiny tach degree setting? 120 degree = 3 sparks per rev
90deg = 4 sparks per rev
60=6 sparks per rev
45 = 8 sparks per rev

 

I just need the rpm function to work long enough to get the right prop.

 

Yeah brand new got 6 hours on it.

 

I guess worst case I have an expensive hour meter.

 

Bob aka skinnydippin gave me some ideas on props but he has his motor higher up on a jack plate

Hull is a shadowcast
motor 25 hp 2 stroke mounted with cav plate in line with roof of tunnel.
weight - approx 500lbs with fuel, motor, battery, gear, not including anglers.
rpm's no clue

 

Yeah I wasn't sure if the height was going to make a big difference or not.
I took it out tonight and played with the settings on the tach. After some trial and error I got it figured out.
It idles in neutral at 2000 rpms. Once I put it in gear at the lowest throttle possible the rpms drop to 980-1000 and max out WOt at 5350 which seems about right.
The manual says max rpm's 5000-6000

With an android gps app on my phone max speed topped out around 32mph. Right around 30 you can feel the boat starting to walk side to side tilll I engage the tabs and drop the bow a little.

 

Thanks for the feedback especially the rpm range from creek runner. I wish the owners manual would specify the whole RPM range rather than just the max rpm. I looked at both the merc and tohatsu manuals and coudln't find anything about the rpm's other than the max. Hopefully I caught this before there was any damage done.

As much as everyone has mentioned the tiny tachs lack of accuracy it saved me a big headache. Having run a 4 stroke for the past 5 years I really had no sense of what normal was supposed to be going back to a 2 stroke. After the tach was hooked up and it read so high at idle I almost dismissed it as a complete misread on the tachs part. The only thing that had me thinking it could be right was the fact that it topped out on RPM's right where the manual said it should.


Long story short I took the boat out tonight and adjusted the idle screw. Someone at the factory didn't count their turns correctly during assembly. I had to back it out almost one full turn. I ended up just above the stall point where it didn't want to shake and sputter. Neutral is right around 950 in the water. In gear at the lowest throttle is 850.