Setting RPMs on a 4S Tohatsu MFS 18B2

[danstead]

Gentlemen,

I'm wanting to verify I have my rpms set correctly and just recently attached a digital tach. Images attached. Per the tach manual, it stated to wrap the wire around the coil. I've also seen statements to wrap the wire around the top plug wire, which would you recommend?

My service manual states 900 rpm in gear after engine is warm, Thru the years I've slowed down the rpms, trying to reduce my trolling speed to under 3 mph.
Can a low rpm setting cause a reduction of vacuum pulling fuel from the slow idle jet?

Any input is greatly appreciated.

Dan

 

[pvanv]

It won't have a stable idle much below 900. Buy a lower pitch prop to go slower.

 

[MattFL]

Or toss out a sea anchor like this, or 5 gallon bucket on a rope, etc... to slow you down. But to get the tach working, wrap the wire around any plug wire and you should be fine. Some motors spark on every revolution and some on every-other, many of those little tachs will have a setting for this. If the RPM being displayed is obviously wrong (off by 1/2) then look for that setting.

Edit--> the forum is giving me trouble recently, google "sea anchor", it's like a small parachute for the water.

 

[danstead]

I have been using a drift sock to reduce trolling speed. Now just want to get motor running correctly and learn more about how carb functions at slow idle and tach installed correctly. Thanks for response

 

[Sea Rider]

Yep, the pick up signal wire must be wrapped at least 4 times around any spak plug cable,



Once set, must adjust the Spark/Pulse Input firing sequence setting to 2 spark per revolution or will count double rpm in the display. Some induction tachs must be grounded, some doesn't, depends on tach brand and model. What's the current rpm reading at idle ?

Happy Boating

 

[danstead]

HEY SEA RIDER
thanks for input, will let you know once i switch wire to from Coil to plug wire. My tach has Count settings.
dan

 

[Sea Rider]

HEY SEA RIDER
thanks for input, will let you know once i switch wire to from Coil to plug wire. My tach has Count settings.
dan

You're Welcome Dan,

Just curious, what rpm was the tach reding while having the pick up signal cable wrapped around the Ignition body as seen in the picture, or didn't have the time to test while the OB was running ? Once the 4-5 cable turns are wrapped tight on the plug cable, roll 2 full turns of electric tape on top of them to hold them better in place...

Happy Boating