Oiling up is just a guess - I recently fitted a 1980's Johnson 70 to my speedboat and took it for its first run yesterday. It runs like a dream, but the (Scottish) Loch we were on has some areas with speed restrictions and we noticed that after about 10-15 mins of running slowly, the engine starts to souund a bit rough - misfire would be a guess. Giving it quick rev clears this out and it runs fine again for a few minutes then reverts to this misfire again. I suggested oiling up, as when I rev it in this situation it gives off quite a lot of smoke, and I noticed that when we were driving it onto its trailor it had left quite a bit of oil in the surrounding water which left an oil line around the hull of the boat. At speed, the engine runs like a dream, and even running slowly for 10-15 mins runs like a dream at low revs - then it starts!
For further info - the fuel I used is a mixture of what has been lying in the (plastic) tank for 2 years (about 10 litres all pre-mixed 50:1, from when I last used the boat with the old engine). This was kept in clean conditions despite the duration. I added 20 litres to the tank before taking the boat out yesterday and 400ml of 2 stroke oil (50:1 at my estimate). The 2 stroke oil I bought yesterday was just moped oil, as I couldn't get outboard oil, wondered if that might make any difference?
Any advice would be appreciated.
Thanks, Paul
For further info - the fuel I used is a mixture of what has been lying in the (plastic) tank for 2 years (about 10 litres all pre-mixed 50:1, from when I last used the boat with the old engine). This was kept in clean conditions despite the duration. I added 20 litres to the tank before taking the boat out yesterday and 400ml of 2 stroke oil (50:1 at my estimate). The 2 stroke oil I bought yesterday was just moped oil, as I couldn't get outboard oil, wondered if that might make any difference?
Any advice would be appreciated.
Thanks, Paul
