I had a problem yesterday with my aux engine, a 4 stroke Johnson 6hp (= white rebadged Suzuki DF6) about 3 years old and I guess about 20hrs run time from new.
Just fired it up for a run as it was a nice day - I like to run around on it for half an hour or so every once it a while, just to make sure it works in case I need it in a hurry one day - and it didn't...
Ran fine for about 2 min, chugging along on about half throttle and then I gave it a burst of full throttle and cough splut phut and it expired. It would start with a lot of persuasion and quite a bit of throttle and run roughly but not right.
Back on shore after a bit of investigation I found it seemed to be down to contaminated fuel as the fuel in the carb was quite cloudy, so I took the tank off, swilled it out and pumped clean fuel through the engine (pull it with the starter cord and it pumps fuel through from the tank) and out the carb drain until it ran clean.
No idea how this happened - the last time I used it I ran half a tank of fuel through it and it hadn't been topped up so how it suddenly ended up with muck in it is beyond me but anyway it seemed to be the problem. The fuel tank is a stupid design with the pipe more or less right at the bottom so any crap helpfully goes almost straight out the outlet save for about half an eggcupful in a small recess at the bottom. Handy thing on your emergency aux ... ho hum.
I also took out what I think is the main jet (I don't have a workshop manual) and blew it out with an airline but it is still not right running in a tank of water to give about the same back pressure as the normal "sea level". It will start with some throttle and a couple of hard pulls (normally easy first pull and no throttle once it has been running that day) but idles quite high and if you open the throttle suddenly it dies and sometimes pops back through the carb. When you close the throttle it either doesn't drop back to proper idle revs or it takes a very long time (30 to 60 sec) to drop back and then only very slowly once it does. It still doesn't rev cleanly when you open the throttle sharply. I haven't done a "power check" yet as it means putting the boat back in the water but there doesn't seem to be any point until I get it running right in a tank, and I know it does normally run ok in a tank as I have used it for flushing in the past.
In the attached photos the bottom red arrow is the carb drain and can anybody confirm the top one is indeed the main jet? Does it have a separate idle jet? (I can't see anything that looks like a jet anywhere else, and I don't know what is under the sealing plug next to the jet but I assume maybe a sealed mixture screw?)
Spark plug is quite sooty after a bout of rough running - though it was clean when I took it out after first getting back on shore, looked normal, and in good nick.
Any ideas about what I might have missed? Nothing else on the engine has ever been fiddled with, I have owned it from new and it is only low hours. I obviously need to get to the bottom of it as it is my emergency engine and one that might work or might not is not a lot of use. I wonder if it will clear itself after a bit of running under power next time out, but of course that will be when I want to go somewhere, and finding I still don't have an aux that is working properly will not be convenient.
Any thoughts would be much appreciated, ta