yamaha 70hp etlh 1987

by Dave W
(Reno, NV)

Hello Again. I appreciate any ideas. Can't go past 1500 RPMs @ WOT. I have had this outboard for over 15 years, it's on my 1988 15.5 ft Boston Whaler SuperSport and I know her and Maintain like crazy.

Our First launch this year as I ran across the lake I noticed I could only get around 3000 RPMs or so. Then After picking up my better half @ camp, couldn't get past 1500 RPMs.
I don't believe it's overheating because the problem is there before it's even @ running Temperature and after and no buzzer. Plus while testing last Friday @ lake I bi-passed the Thermo sensor @ the Head.
Here's What I've done so far. New throttle Cables 2 years ago. New 703 control box 5 years ago. Replaced Lower unit with rebuilt one at the end of last season. Rebuilt the H2O pump. I've replaced the Thermostate. Replaced the fuel pump, cleaned the fuel filter, inspected the fuel lines, have run it on 3 different fuel tanks (I keep STA-BIL 360 Marine in the fuel at all times) Gone through every ground and bullet connector and eliminated any corrosion I could find. Tested spark (seems good but that's only while dry cranking). Checked Throttle cable and all motion of linkage including Magnito Advance (not running, I do not have a test tank).
So now I'm Wondering about the C.D.I. UNIT ASSY or the possibility that it suddenly lost Dynamic timing? or any part within the Magnito System that would allow it to start, idle but not go past 1500 RMPs? It's a Steady 1500 RPMs, no wavering. And not ruling out Carbs

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