I had a similar problem with a merc 60 2 stroke and someone had fitted a 4 stroke tacho, giving me some really odd readings.
I fitted a tiny tacho and set it I think to P2? round one of the Ht leads etc.
Mine gives very accurate reading and max rpm readings but I needed the tiny tach instructions to get it properly sorted, you can down load them from the web.
I also soldered an extended wire on mine, and it still worked fine so it dash mounted and easier to read etc.
On my boat and Ht lead came off dropping the max rom etc to about 4500 not 5500 took a while to work it out............
Mine now runs a 13pitch 10 3/8 stainless prop and reaches 5400-5500rpm, tried a few props to get this right.
Hope this is useful but this is for a Merc engine.............2005.
Originally Posted by chris123
Is there any possibility that it could be the wrong Tinytach for your outboard? What revs are the Tinytach / boat rev counter showing in neutral at idle? I'm guessing the revs you are getting at WOT are about half what they should be?
My experience with two strokes ended with a Yam powervalve (bike) about 15 years ago, but I would have thought if the required idle is (say) 900rpm, your outboard will either idle like a bag of nails at 500 rpm, or will stall.
If the idle appears to be smooth (well, smooth for a 2 stroke
) and the tacho(s) do indicate 500 rpm, I would still suspect the tacho.