Retune a Detuned...???

[AK4Dave]

I just bought an 18' Valco w/ a 1990 detuned Johnson 40 which is called the "Alaskan 35". Yesterday when I applied water to it via the garden hose, and started it up, I noticed that it would accelerate normally but when I gave it max throttle, when it got to a point, the RPMs stayed the same when there was still plenty of throttle left. I am assuming it is because of it being detuned....as in, there is some type of a governor? I called the previous owner and he said he thought that was the reason as well, but also said it was always able to get up on step easily with 4 people aboard. So it still had plenty of power. I haven't called the local dealership yet, but thought I would ask here first. I'm wondering if it may be a simple matter of "retuning" it back to the max 40hp? The "Alaskan 35" was made this way because of the HP restrictions on the Kenai river. They did the same with the 50hp. As 2 stroke motors are no longer allowed on the Kenai river, I have no need for the detune. But I would like to have max HP when I travel across the Cook Inlet as well as the large lakes I like to boat on here in AK. Is anybody here familiar with the detuned outboards?
Thanks....

 

[coolguy147]

Re: Retune a Detuned...???

nope dont know

 

[jtexas]

Re: Retune a Detuned...???

The easy way to find out would be to remove the air silencer cover and see whether the throttle valves open up to horizontal.

BTW, revving your engine above 1500 RPM or so on the muffs (except as needed to warm up a cold engine) is risky. If you have any hotspots in the combustion chamber, from carbon buildup or whatever, they can preignite the air/fuel charge, and without backpressure on the exhaust the unloaded engine can race uncontrollably, way beyond its design maximum RPM -- enough to literally tear itself apart. The throttle and spark plugs are both irrelevant at that point -- the key won't turn it off, even pulling the plug wires will have no effect. It's called 'thermal runaway" or "preignition runaway".

 

[AK4Dave]

Re: Retune a Detuned...???

The easy way to find out would be to remove the air silencer cover and see whether the throttle valves open up to horizontal.

BTW, revving your engine above 1500 RPM or so on the muffs (except as needed to warm up a cold engine) is risky. If you have any hotspots in the combustion chamber, from carbon buildup or whatever, they can preignite the air/fuel charge, and without backpressure on the exhaust the unloaded engine can race uncontrollably, way beyond its design maximum RPM -- enough to literally tear itself apart. The throttle and spark plugs are both irrelevant at that point -- the key won't turn it off, even pulling the plug wires will have no effect. It's called 'thermal runaway" or "preignition runaway".

Thanks about the info about reving the engine on the "muffs".......that's the first time I'd heard that.
I'll check the throttle valves and see. Is that the way they detune an engine, by not allowing the throttle valves to open up fully?
Thanks Again...

 

[jtexas]

Re: Retune a Detuned...???

I really don't know for sure. It's the first thing came to mind when you said "...there was still plenty of throttle left."

 

[AK4Dave]

Re: Retune a Detuned...???

The easy way to find out would be to remove the air silencer cover and see whether the throttle valves open up to horizontal.

Just wanted to let you know that you were right. It seems as tho all they do is throw on a different throttle cam with far less arch so that it doesn't move the roller anymore to open the valves all the way. So all I need to do is get a regular one. I have one for a 50hp Evenrude that I was hoping would work, and it would, but the the bar and yoke are a different size and length. Thanks for the input.

 

[jtexas]

Re: Retune a Detuned...???

hey thanks for the feedback...

you can find your part numbers at www.shop.evinrude.com click on 'electronic parts catalogues"