Hello fellow boatsmen,<br /><br />Johnson 50 '84, Mod. nr. J50BELCRM<br /><br />Introduction: <br /><br />We are experiencing various difficulties and anamolies with this engine, all probably related to a single mechanical/electrical problem. I will try to explain what these are and provide, hopefully, the most relevant information. I encourage you to ask any questions if there is anything I have left out that you feel is needed, in the end I hope for tips, ideas or a solution to this issue. I have copy/pasted from some previous text that I have written on this, and I apologize if it sounds repeating and maybe incoherent sometimes. I have also provided a link to a video I made of the engine operating in a test tank to give more, and maybe more accurate indications of the issue.<br /><br />The problem as we experience it: <br /><br />The engine starts very easily, this is one of the differences we noticed after cleaning the carburators as fully explained in the section below. It does however have somewhat problem with that it stops shortly after cold starting and it takes several attempts with choke on/off before I am able to keep it running. I have also done a thorough inspection on what goes on when I give throttle alone with the linkage connecting the two carburators. And what I noticed is that it seems to missfire/backfire frequently. This happens only when I apply throttle, in idle it runs kind of ok. We also have problems with running this engine at high rpm's, if I try to give throttle, it just dies suddenly. This happens, even though we have let it run for at least 10 min., letting it get warm. Operating it in the water, in forward there is a limit on how much throttle it will accept before it dies, on this threshold it acts kinda jerky. If i try to add more throttle slooowly, it dies. While in this threshold I tried using the squeze bulb on the fuel line from the fuel tank, to see if the fuel pump was bad, but no help. I also tried running the starter with the fuel line disconnected to check the stream, and sure enough there is a pulsating stream of fuel from the fuel pump.<br /><br />It looks like the top plug is more wet than the lower plug. Also after further testing today, I have noticed that if I remove the top spark plug lead, the engine runs pretty ok even though it is running on the lower cylinder alone. If I reconnect the top and disconnect the lower, so that the engine is only operating with the top cylinder alone, it seems to stumble more, just barely running in contrast to running the bottom cylinder alone. Another thing, when the lower is disconnected, sparks fly from the lead, also saw sparks directly from the coil firing to the powerhouse. This does not happen when I remove the top spark plug lead however.<br /><br />I have provided a video of the engine operating in a test tank, hopefully this will make it easier to give you a picture and indication on what might be wrong. The video was taken with a Hi8 camera and recorded to the computer with a TV-Card and the compressed using DivX, so the quality is hard to maintain, and the filesize is rather large. Therefore I provided two files so you can decide, first one is made short and might be enough for you to consider, otherwise there is the full version which is 4 minutes.<br /><br />I have a ok upstream ( about 868 kbit ). Please don't download "just to see", this will make it harder for people serious about helping me sort this one out. Thank you.<br /><br />You might need a codec first, download this for free here.<br /> DivX Free Codec Download <br /><br /> Johnson [ 13,0 MB (13 635 424 byte), Duration: 0:42, DivX ]<br /><br />Johnson2 [ 64,5 MB (67 686 882 byte), Duration: 3:54, DivX ]<br /><br />What we have done so far to remedy this issue: <br /><br />I have tried to overcom this issue by servicing the carburators, disassembling them, and with that replacing the inlet valves on both carbs. I followed the steps from the repair manual when servicing the carbs. cleaned them, and removed any potential debris/dirt in any of the orifices. To my understanding there are no tuning screws, so all was just fastened as explained in the manual, synchronization was also done accoring to the manual. We have also replaced and fixed any potential problems with the fuel lines, also, I have tried the fuel pump by running the engine with the starter, and there _seems_ to be a good flow of fuel from the pump, also cleaned the filter with that. After letting the engine operate for some time, I notice also that there is fuel in the chamber which could also be a indication of sufficent fuel supply to the carbs.<br /><br />I would also like to let you know that we have also replaced the impeller, fixing our previous and probably unrelated problem of engine overheating. After we noticed the overheating warning sound we were very carefull not to let it run in a state of overheating, as this obviously can cause serious damage to the engine.<br /><br />As my friend is a car mechanic he had access to equipment that let us measure the compression in the cylinders, and from my understanding the measurement is almost more than you can expect, good compression and very small variation between the two cylinders.<br /><br />Thanks for your patience.<br /><br />Hope someone can help !
