1987 Yamaha 70hp ETLH newest problem.

[Whaler785]

my 1987 Yamaha 70hp ETLH newest problem.
Hello All. I appreciate any ideas. Can Not get 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.
 The First run this year, ran across Lake and was only getting around 3000 RPMs @ WOT, not right. Picked up my better half @ camp and from there got worse, only 1500 RPMs, when we gave up and left after 3 days, anticipated long run to the ramp but suddenly was screaming across @ 4000 RPMs, once I got there and stopped, tried to throttle up again and back to 1500 RPMs which is where it's limit is now. It's a Steady 1500 RPMs, no wavering.
I don't believe it's overheating because the problem is there before it's even @ running Temperature and after. 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 Advancelools right(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? and like I said, It's a Steady 1500 RPMs, no wavering. Not Ruling out Carbs but all seems normal except the 1500 RPMs

[RickK]

It sounds like the problem I had on my '91 Yamaha 250 - the internal oil tank was not getting the low oil signal to the external oil tank for refilling, so the engine, which did get the low oil signal dropped into survival mode and is limited to 2500 rpms, yours could be 1500 rpm.  It ended up being the computer needed to be replaced.

[Whaler785]

Thanks, I have been suspecting the CDI. Going to the lake tomorrow and my Mechanic is going for a boat ride with me.
Do you know what wires need to be tested for that?

[RickK]

No I don't - sorry.

[wingnut]

I had a similar problem on my 87 115 Yamaha as well. They say the CDI is "unlikely to fail" but it can, like anything else, especially on a 33 year old motor. Like yours it was limited around 1500.

I'm not aware of any wires that can be checked with a multimeter to see if it's working... To my knowledge, CDI isn't like a rectifier regulator where you can test across the right circuits and see if it's bad; it's a pretty complex computer. Perhaps someone else has more info/methods than me though.

 Thankfully replacement is easy, just a little pricey ($660 for a new Yamaha one, if I remember right?)

I found a new aftermarket CDI on eBay for less than half price (you can find them used there too).

[Whaler785]

my mechanic thinks it's a carburetor/maybe reed problem, can't find any electrical problems.

[RickK]

Let us know what he finds.

[Whaler785]

Roger that, feel naked, He and my boat are 100 miles away @ Eagle Lake ;-}

[Whaler785]

1987 Yamaha 70hp ETLH, so I'm still dumbfounded. What I've done 2 date in order. Replaced Lower unit last fall with a remanufactured one which is the last time it ran great (around 50 hrs on that L.U.). Have drained it twice, lube looks great, no-slip, etc. So my RPM problem persists (Underload Only)! after replacing all fuel, fuel tank fittings, new OEM fuel pump, I have personally gone through every bullet connector and fixed any corrosion, had my mechanic first recheck the compression, 100-105-100, not brand new but still not terrible (max hp on my 88 Boston Whaler 15ft SS is 70hp and it seems this is enough compression to literally scream still like last fall, fully loaded with 3 passengers and lots of crabbing gear). He also checked Timing Advance, Plug Fire, etc. Can't find any electrical issues. Got out my wallet again and had him rebuild all 3 carbs. Went for a lake test, The Boat now empty, except for myself. Still Won't Get up on Plane. So while out in the middle plowing through the H2O @ 200o RPMs I left the Helm and went to the front stood on the bow to weight it down and little by little RPMs start raising, go back to the helm and, Damn if I'm not going 4000 RPMs (Trim & Tilt Works same as Always). Turns out this is the only way I can get the thing going WOT. 3 things come to mind. Could the CDI just not be responding correctly? Can the remanufactured Lower Unit have an issue even though it shows no problems? Bottom paint? needs repainted but that's never slowed it down before. I can't give up @ this point

[Whaler785]

Also, wondering now about the Stator?