Oil ratio and trolling....Motor

[Wiggy]

I'm running a '85 Mercury 20hp on 1:50 TW-3C yamaha mix with unleaded. After about 10-15mins of trolling at an idle pace or slightly faster, the motor starts coughing and spluttering. When I give the motor a good opening up for about 30 secs there's lots of blue smoke which then clears and it purrs again.<br /><br />My question is, can I reduce the oil in the fuel or do I risk serious damage whilst running at WOT? What can I safely reduce it to? Is there a happy middle point?<br /><br />I use the motor to both getting out to my favourite spots and then trolling. In the future an electric motor is going to be brought for trolling, but only when funds allow.

 

[JB]

Re: Oil ratio and trolling....Motor

Stick with 50:1, Wiggy. It is needed for high speed operation, though most outboards can idle or troll on as lean as 150:1.

 

[LubeDude]

Re: Oil ratio and trolling....Motor

If its fouling the plugs and smoking as you say, it has too much oil for the application. JB is right, at an Idle an engine can easily get by on 100:1 or even leaner.<br /><br />I have friends that carry two tanks, one at the recommended 50:1, and the other at about 100:1 for trolling.<br /><br />You will be much happier and you will do no damage. Be sure to switch back on the trip back.

 

[Wiggy]

Re: Oil ratio and trolling....Motor

Ah great idea about the two tanks, I may adopt that idea. Thanks guys.

 

[Silvertip]

Re: Oil ratio and trolling....Motor

If you use two tanks, be sure to mark which one is the lean mix. Either that or use a smaller tank for the lean mix as you will use far less fuel at trolling speeds. I suspect however, that your engine needs some carb work. A 20HP Merc should troll for days without loading up.

 

[Wiggy]

Re: Oil ratio and trolling....Motor

I have taken off the carb and had a look at the various parts, and all looks clean. To be honest, when I got it a few days ago it was coughing and spluttering. I changed the plugs and it didn't do it as much afterwards, but still continued a little. After a days driving at WOT most of the time, it's loads better with just some coughs and splutter at WOT. I was putting this down to a air leak in the fuel connector (which it has). Maybe I'm wrong?<br /><br />I'm not exactly an expert, but learning all the time, so advice is more than welcome. I have some spray solution that you spray into the carb for winterising, would this help? The motor isn't the easiest to start either.

 

[Silvertip]

Re: Oil ratio and trolling....Motor

If it's coughing at wide open throttle, I would not run the engine until you've determined what's going on. Those coughs are signs of a possible lean condition. Two-strokes don't like lean and the result of prolonged operation like that can burn pistons. If you think its and air leak, check all hoses and connections. Don't just look at them. Pull and tug and make sure the hoses don't aren't checked or cracked. Looking at a carb does not prove anything. Its the small jets and internal passages that get plugged with varnish that causes the problem. Carbs need to be soaked in carb cleaner and blown out with compressed air and then reassembled with new kits. Your problem seems to be a rich condition at slow speeds which may be due to an inlet needle and seat problem, or the float setting needs correction, or the float itself may be porous and allowing improper fuel levels in the float bowl. And finally, make sure you have good spark. A crisp blue spark is required for proper operation.

 

[BoatBuoy]

Re: Oil ratio and trolling....Motor

What Upinsmoke said. And when you get it running right, the smoke problem at idle may get better w/o changing fuel mix.

 

[JB]

Re: Oil ratio and trolling....Motor

"Looking clean" means nothing in small engine carbs, Wiggy. The places that cause the most trouble are too small to see and/or not visible.

 

[Wiggy]

Re: Oil ratio and trolling....Motor

Well it looks like a carb clean is in order. I did take the cover off to the float, and that felt like oasis (the stuff florists use to stick plants in for arrangements). I'm in Norway and the availability of gaskets and things for older outboards are non-existent, can anyone recommend a good cheap source of spares that ship abroad?<br /><br />I felt when driving at WOT it helped if I squeezed the fuel pump bulb now and then to inject more fuel into the carb. The engine ran a little smoother anyway.<br /><br />I have a Seloc manual for this motor, and hopefully with my less than novice abilities, a can sort it out.<br /><br />All advice is greatly accepted, and please put into novice terms!!