1983 Johnson 15hp problem

Hello Everyone! I'm new to the forum and just purchased my 1st boat last week. Here's a little history of my problem...I purchased a 16ft Jon Boat that was outfitted with a 1983 Johnson 15hp. The gentleman that I purchased it from said that he no longer had time to use the boat and it had been sitting for a while.

When I got the boat home the motor would fire up with no problems but ran a little rough. Having been told it had not been used, I took the carb off and sure enough it was a little gummed up. I cleaned the carb and re-installed it. I dumped the old fuel and replaced it with fresh gas and I replaced the fuel line and primer bulb from the tank to the engine with a new set. Running the motor in my yard it seemed that I had corrected the problems with the fact that it had not been used frequently.

Now...the next day i took the boat down to the river to try it out. The motor fired right up but when I tried to go wide open, the motor didn't seem to have the response that it had in my yard. The RPMs would flucuate up and down and never could get the boat on plane. After adjusting the knobs for idle and rich/lean with no change in the way it was running, I eased out on the choke and the engine came to life and the boat got up on plane and it was smooth as glass with no flucuations in the RPMs or anything. It ran just like I had just purchased a brand new motor. But when I pushed the choke back in or "off" it went back to running poorly.

I know that pulling the choke out tells me that it is robbed of fuel and running lean. I checked the fuel filter this morning and it seemed to be ok with nothing in the screen that would block fuel flow. I did notice that when it was running rough, I sqeezed the primer bulb and it didn't seem to want to open back up. It stayed partially collapsed after I squeezed it. I am absolutely new to outboard motors and just transferring my knowledge of ATVs and carburetors to this. What else can I check or what could be causing it not get enough fuel? The fuel tank itself is pretty old and that is next on my list to replace. Could the fittings that attach the fuel line be gummed up as well or is this not common. I have also checked my fuel lines for kinks and all looks good there.

What is really confusing to me is how well it seemed to run in my yard but not so much in the water. I know that the engine is under more of a load in the water but it doesn't seem to be starved of fuel when I run it out of water.

Thanks in advance for any input that you have to offer!

Re: 1983 Johnson 15hp problem

ok im the kinda of person that when i get something from someone else i like to eliminate ALL the bugs and start anew as best i can this lends more days fishing and less working on my stuff
so if it where mine and i had just bought it id put a little cash into it

buy a carb kit tear the whole thing down to parts soak overnight in can of carb cleaner (not the
spray stuff) and rebuild it kits are about 20 bux

http://www.marineengine.com/newparts/part_details.php?pnum=OMC0398453&ptype=&Engine=&Model=

rebuild the fuel pump another 15 bux

http://www.marineengine.com/newparts/part_details.php?pnum=OMC0393088&ptype=&Engine=&Model=

replace or clean the fuel filter (you can swish the element around in the can of carb cleaner to clean it just rinse it out with water DO NOT leave it in there overnight) blow it dry or leave it to dry ovenight

you should be good to go after that id imagine you didnt tear into the carb quite far enough and thats why youre having trouble but on a motor like this spending 50 bux on it now will save you hours of headache later JMHO

Re: 1983 Johnson 15hp problem

oh and all two strokes will run beautifully until they are put under a load and id also change the waterpump
http://www.marineengine.com/newparts/part_details.php?pnum=SIE18-3400&ptype=&Engine=&Model=

Re: 1983 Johnson 15hp problem

Agree that the carb. is the likely suspect for your problem. You should do a compression check and confirm spark on both cylinders just to eliminate those as possible concerns. Are you certain your tank is vented? You probably have a fine motor but you'll have to work through some bugs to get it to the reliable condition you want. A new impeller should also be towards the top of your list once you know the compression is reasonable. Have a look at the "Top Secret File" at the top of this forum as there are lots of great pointers for you to consider and check. Also look at this link nearer to the bottom of the page. http://www.sschapterpsa.com/ramblings/Ramblings.html I consider it a must read for all us 9.9 and 15 owners. Best of luck. Rick.

Re: 1983 Johnson 15hp problem

Thanks for the replies. I assume that the tank is vented. If not, it would not be able to provide a constant flow of fuel correct? <--when I read this back to myself it sounded like I am being sarcastic but I assure you that i'm not just trying to get a better understanding of a potential problem. And also, concerning the impeller...As i was running the motor I did check and I had a good steady stream of water coming out. What signs to do you look for to know that this may need replacing?

Re: 1983 Johnson 15hp problem

Also, check the screen on the fuel pickup in the tank that could be gummed up after sitting for a long time.

Re: 1983 Johnson 15hp problem

also while you have the carb apart take a small wire an push it thru all the tiny holes on the carb body some on here say a bread tie with the plastic removed works well

Re: 1983 Johnson 15hp problem

Re-clean carb and replace the 5/32" hose from pump to carb. If that one gums up there's no screen to stop the gunk from going directly into your carb.

Re: 1983 Johnson 15hp problem

Steady flow of water from the telltale and after warm-up, the water should be warm as the t-stats open.
Also, all of the recommended fuel system checks plus the diaphram. These can age and get gummed up and/or tear which would cause a fuel delivery issue. If she's been sitting that long, you will better serve yourself by going through all these system maintenance suggestions. Those are great little motors and will give you plenty of years of enjoyment.

Being new to outboards, there's a "sticky thread" at the top of this particular forum from poster,
'tashasdaddy' (RIP) called "Top Secret File", that once you open it has a lot of great links that are very helpful on these old johnnyrudes. There's even a "starting an older outboard after it's been sitting" thread. Welcome to iboats, by the way.

Re: 1983 Johnson 15hp problem

OnTheWaterSC said:

Thanks for the replies. I assume that the tank is vented. If not, it would not be able to provide a constant flow of fuel correct? <--when I read this back to myself it sounded like I am being sarcastic but I assure you that i'm not just trying to get a better understanding of a potential problem. And also, concerning the impeller...As i was running the motor I did check and I had a good steady stream of water coming out. What signs to do you look for to know that this may need replacing?

Click to expand...

Unfortunately the only indicator regarding the impeller is an overheated engine which you want to avoid. The rule of thumb is replace it as soon as you buy a used outboard and then every couple of years from then on. You can adjust frequency according to amount of use somewhat. Regarding the tank being vented, just remove the cap when it's running poor and that will tell you if it's venting. I always check compression first as I've learned that checking it too late can cost a lot of useless activity and expense. I don't mean to alarm you, as I said earlier, you probably have a fine motor. I have an 82 -15 Evinrude which was my first outboard ever. I never use it anymore but it's kind of like my first born and can't imagine selling it. Lots of posters here have given you good advice on things to check so stay with it and I'm sure you will correct the problem. Again, I suspect the carb. Rick.

Re: 1983 Johnson 15hp problem

1) I'd absolutely change the water pump; housing, impeller and all. You don't know how long that old water pump has been in that motor. Plus, you should grease the driveshaft splines and check the overall condition of the lower unit.
2) As far as having to run WOT with the choke on, that sounds like high speed jet in the carb - I'd do like the folks say and tear it down, soak it overnight and rebuild it.
3) The primer bulb staying flat indicates that there is something between the tank vent and the check valves in the primer bulb. Since you have replaced the fuel line and primer bulb, i would recommend replacing the gas tank, dispose of the new gas in the old tank (don't reuse it). Flush out the entire fuel supply from the tank to the carb and make sure that you have an unrestricted supply. Then put an inline filter on the fuel supply line and hook up the carb.

Welcome to iBoats.

Re: 1983 Johnson 15hp problem

Thank you all for the replies! I plan on getting started on removing the carb this weekend and go from there with the other checks and replacing the water pump. Thanks again!!!!!