Jonas_Vestlund
Recruit
- Joined
- Jun 3, 2002
- Messages
- 3
The other week, I encountered a strange problem with a Johnson 70 hp from 1978 (two stroke, 3 cyl.). I have had the boat+engine for about a month now, and the outboard engine has worked fine (nice sound, no problems starting etc) until now. The other day, I started the engine (no problems), let it get warm and slowly drove away from the harbor; the engine sounded fine and did not vibrate excessively or anything. However, when I, after a few minutes, wanted to accelerate, the engine felt powerless and refused to reach high rpm. Instead of reaching max rpm, the engine only reached, say 60%, stayed like that for 5 seconds, increased to 75-90% for a few seconds (without me doing anything), then down to 50-60% of full rpm again, etc. <br /><br />At first, I suspected water in the tank. I bought a water remover fluid which I mixed with the fuel in the (built-in) tank. No improvement. <br /><br />To be on the safe side, I drained the three carburettors by unscrewing the drain plug at the bottom of the float bowl. I collected the fuel which did not seem to contain any water (no visible "bubbles" or layers on the bottom of the glass bottle I used to collect the fuel).<br /><br />Then I changed the fuel filter on the fuel hose and cleaned the filter on the fuel pump in the engine. There was some debris (old paint...) in the filters, but the problem did not go away.<br /><br />Then I changed all three spark plugs. The problem remained. When I investigated the old ones, they had damp black carbon over entire firing end of plugs. One of the plugs was slightly cleaner than the other two. I assume that the damp black carbon is because I may have used a slightly too rich fuel
il mixture, which is strange, since I have been using 50:1 as recommended by the manufacturer.<br /><br />By following a tip from JB in Texas here on iboats, I then found out that one of the three cylinders does not seem to work properly: While running the engine on idle, I disabled the spark plugs one by one. For two of the plugs, the engine started "coughing" and almost stopped, but when I removed the third, the engine just continued as if nothing had happend. In other word, the engine seems to be running on only two cylinders. <br /><br />The strange thing is that also the cylinder which does not seem to work is covered with a thin, damp black layer of carbon, even though I changed the plugs just the other day, after I started having problems with the engine. And another strange thing is that the plug of the malfunctioning cylinder seems to has spark. I tested this by pulling the plastic plug cap from the spark plug of the faultly cylinder, inserting a new plug and holding this against the engine while running. There was plenty of sparks. How can the cylinder not function if there is sparks? Could the carburettor for the faulty cylinder be jammed or something? Maybe the float needle is dirty?<br /><br />I spoke to the previous owner. He mentioned that he had had a similar problem once, that the boat would refuse to reach proper speed. He claimed that a friend had pin-pointed the problem as being rust on the 'igniting coil', but that he did not know exactly how the friend had solved the problem.<br /><br />What is the best way forward? Should I exchange the igniting coil, or all the electric wiring? Or should I focus on the carburettor since there is obviously a spark coming? <br /><br />Greatful for any help or suggestions, I am completely stuck here...
il mixture, which is strange, since I have been using 50:1 as recommended by the manufacturer.<br /><br />By following a tip from JB in Texas here on iboats, I then found out that one of the three cylinders does not seem to work properly: While running the engine on idle, I disabled the spark plugs one by one. For two of the plugs, the engine started "coughing" and almost stopped, but when I removed the third, the engine just continued as if nothing had happend. In other word, the engine seems to be running on only two cylinders. <br /><br />The strange thing is that also the cylinder which does not seem to work is covered with a thin, damp black layer of carbon, even though I changed the plugs just the other day, after I started having problems with the engine. And another strange thing is that the plug of the malfunctioning cylinder seems to has spark. I tested this by pulling the plastic plug cap from the spark plug of the faultly cylinder, inserting a new plug and holding this against the engine while running. There was plenty of sparks. How can the cylinder not function if there is sparks? Could the carburettor for the faulty cylinder be jammed or something? Maybe the float needle is dirty?<br /><br />I spoke to the previous owner. He mentioned that he had had a similar problem once, that the boat would refuse to reach proper speed. He claimed that a friend had pin-pointed the problem as being rust on the 'igniting coil', but that he did not know exactly how the friend had solved the problem.<br /><br />What is the best way forward? Should I exchange the igniting coil, or all the electric wiring? Or should I focus on the carburettor since there is obviously a spark coming? <br /><br />Greatful for any help or suggestions, I am completely stuck here...