Pvany you are my last hope!

[Star]

Your kind of talent and honesty is hard to find. I wish I was closer to Buffalo. I have posted on the mercury topic here and on mercurypartsus.com.. not one response. The Mercury dealers around here don't even know what a 15 hp 4 stroke Mercury/Tohatsu is much less understand it's quirks. I have a 05 15 hp Mercury 4 stroke SN 0T987569. Two years ago I started to have intermittent ignition cut off and on after 40 minute of WOT running. The motor would always start right up and idle smoothly. I have always taken care of my carb and fuel system, although I did have a problem with a 2 year old Mercury fuel line that disintegrated internally that gave me a fit. Once I started up it could run for days without a problem, so I couldn't be diagnosed by a shop. Finally this spring it stuttered and then ran on #2 cylinder only for about a minute. After a short stop trying to diagnose the problem I started it up and it ran fine the rest of the day So I conclude that it wasn't the CDI it had to be the coil. Plugs burn clean although #1 always has a slight brown discoloration on part of the electrode porcelain. They are replaced at least once a season. Compression is 180# on #1 and 175# on 2. Two weeks ago I got a new coil, although the resistance readings were in spec .33ohms on primary and 4.7k on secondary. Boots were also around 4.7k. After a 2 hour carb soak and flushing and reassembly. The motor runs better than it ever has, although I only have about 3 hours on it. The problem I now have is that the rev limiter is kicking in constantly at 5100 rpm, and I think the tach (tiny tach) is setup right it idles at 800rpm. Do some CDI's cut in before the 5500 rpms I am supposed to have. If I buy a new one will it fix this, Could it be a ground issue on the CDI. Yes I know that I can prop up, or get a fishing partner, but I really want that 5500 rpm. I will solve this one way or the other, but your knowledge could save me a lot of guess work.

Thank you for your help on this
Joseph Merriam

 

[pvanv]

Joseph,
Thanks for the kind words; most of us on the board try to help our fellow boaters

The ESG for a Tohatsu MFS15B2 should not engage before 6000 (actually about 6200). You may have a problem with the CD. I would verify the WOT RPM with a good shop tach (some low-cost tachs are not 100% accurate). If the ESG is indeed engaging at 5100, and all connections (including grounds!) are good, a new CD is indicated.