Swapping an M90A for an NS140

Hi All,

While looking to look repower my old boat from an old M90A for something with more power, I came across a NS140A with a brand new powerhead that has less than 10 hours on it (very stoked). Picked up the motor and controls last weekend. Planning on leaving the old controls in place hoping for an easy "plug and play" installation. The only difference I saw from the wiring was an extra red plug on the 140. When I saw the new motor run in person, if this plug was not plugged in from the main throttle/control, it would not idle/run correctly. When plugged in, ran/idled perfect. My question-- I don't see the other end of the of that wire from the original M90A controls/throttle end. Anyone know what the plug is? Mechanic was a Johnson/Evinrude guy so wasn't too familiar, mentioned it might be something that controls the timing? in looking at the engine diagrams, it says something about coming from CD unit....i think. Just wanted to see if anyone was familiar and if there is a way to bypass. I have the set of controls that came with the motor but would like to avoid running them through the boat as that would create a lot of extra work.

Thanks in advance.

Tom

I have no clue what you are describing. Both the 90 and 140 use the same harness to the control, with a large connector, plus the two tilt wires. Since the controls are identical (3 screws to attach), it should not matter if you want to swap controls. Since the ignition on these is not "battery" but rather "magneto", I can't imagine any wire that would affect idle. Here is the RC5E (140) control wiring diagram:

Thanks, Paul. I’ll circle back with the project and let you know if it was an oversight on my end.

cheers,
Tom

Hey Paul,

So i pulled the 90 off today and noticed that there is no red wire with the yellow stripe (white clip). This was the the clip that i mentioned made the motor run better when i looked at it. Do you happen to know exactly what that wire does for the 140? i know the blue and pink are for the trim, im just not certain what the thrid wire with the white clip is for. Ive included pictures below of each wiring harnesses from each of the controls.


90 controls


140 controls



Thanks,
Tom

The 115, 120, and 140 have a low-speed RPM limitation. That is the Red/Yellow wire. If that is open (not connected), the speed will be limited to 1500 RPM. See page 7-64 of your Factory service manual. I can get you that book. I would install the RC box for the 140 to connect that wire.

pvanv said:

The 115, 120, and 140 have a low-speed RPM limitation. That is the Red/Yellow wire. If that is open (not connected), the speed will be limited to 1500 RPM. See page 7-64 of your Factory service manual. I can get you that book. I would install the RC box for the 140 to connect that wire.

Click to expand...

Thanks, Paul.

When I traced that wire up to the 140 control box, it seamed like that wire just goes to a hot wire to the key. So when the key is turned to the On position it gives that red and yellow wire power... If this is the case, I guess I can just run a wire up to the key on the 90 control box. (The 140 box is pretty banged up which is why I’m not using it)

That would work.

Boat has been running great all summer until the other week...Lower cylinder has water in it... Milky plug. Checked head bolts on head and they are torqued at right spec. Compression tested and am seeing 120 across all four. Is it possible that the gasket is shot while still maintaining that compression reading? Are the exhaust gaskets pretty common to go? I just want to find the next best direction to go in...

If i go the head gasket route, does anyone happy to know if you have enough room to get the bottom bolts out? or does the whole powerhead need to be removed...

Thanks,
Tom

Possible to have a leaky gasket; it might only leak at certain temperatures, so compression won't necessarily show that to you. You could also be ingesting some water through the intake, depending on splashing. AFAIK, you would pull the power head to get to the lower bolts.

Thx, Paul. I guess try the head gasket first.