Outboard not running smoothly unless at full chat

[MoodySabre]

I have a Johnson 3.5 2-stroke for my 2.3m inflatable dinghy. Starts first pull and keeps going. But it sounds rough. If I put it on full throttle then it sounds smoother but is of course noisy and scares the Mrs as we go into warp speed.

Would I be better off with a smaller outboard working harder? (a smaller one would be lighter too). I'm a bit reluctant to change from something that seems reliable just because it doesn't sound as though it is.

 

[David2452]

Probably just four stroking a bit at lower revs, treat it to a new plug with the right gap and make sure you use good TS oil at the correct ratio with fresh(is) fuel.

 

[ProDave]

Interesting thread.

I have a Mariner 4 two stroke.

Most of the time it is fine.

but occasionally when motoring at low throttle, it will be running fine and smooth, then it will suddenly drop it's revs very slightly and sound a bit "rough" (you can see it vibrate on it's bracket a little) then it will go back to normal.

I've often wondered what it is, and hoped one day I might have my camera handy to take a video of it. It wondered if somehow the timing was going to pot for a while, but could not think of a mechanism that would do that, then go right again.

 

[VicS]

+1 on the four stroking idea. It's quite unmistakable but cannot describe it. Tends to happen more when lightly loaded.

It indicates that perhaps it is running a bit rich.

I assume the engine (OP's) is post 2001 and is one of the ubiquitous rebadged Tohatsus.

IIRC the mixture is adjusted by moving the needle in the throttle piston up or down a notch at a time. Might be worth lowering it a notch for a trial. The worse that can happen is that it'll need a bit of choke to keep running.

Seagulls tend to do it. Adjusting my Featherweight is a compromise between not four stroking too much and not needing the choke on for a bit longer

 

[cliff]

In order -
Plug - treat it to a new one,
Carb - clean it well especially the slow running jet then clean it again,
Fresh fuel , correct mixture, and ob 2t not lawnmower or chainsaw 2t
reset carb mixture
Enjoy many more years of phuttering about

 

[Vitesse]

Cliff speaks words of wisdom!

 

[macd]

I have a Johnson 3.5 2-stroke...Would I be better off with a smaller outboard working harder? (a smaller one would be lighter too).

Unless you buy second hand, it probably wouldn't be lighter. It'd be a four-stroke.

Do what Cliff says. It probably just needs a little love.

 

[DownWest]

+1 for using the correct oil. Air cooled garden stuff runs hotter than a water cooled O/B. A good carb clean might sort the low speed running too.

To ad: My most reliable O/B is a 1980 3.5 hp air cooled Yamaha. Old fuel after several months...second pull, off she goes.

 

[cliff]

 

[MoodySabre]

Thanks folks (and for the musical ) - it's had a DIY service and fresh fuel so will try a new plug.