motor idles rough,smokes,coughs

[Tommy Miller]

I need some help with a few questions. I have read many of these posts and still am not sure. I have a 1974 Johnson 115 hp motor that sat up for 10 years before i bought it. My boat man that I have used for 10 years rebuilt it. the cylinders were scored and the motor got bored. It got new cylinders,rings ect. He cleaned the carbs for days. The job was over 1000.00. Anyway I can not get it to start with out starting fluid, starts fine after that. It runs rough at low RPMs and coughs and sputters some. the motor runs fine at the higher RPM range. It smokes all the time and more when it coughs and sputters. It has all new gas lines with a filter. It is a two stroke so I mix 50:1 with high test gas(shell only). That is what my boat man suggested. no ethanol in gas. The spark plugs looked black and wet with gas/oil mix. I have sprayed carb cleaner through it more than once. My boat man does not seem to know what else to do. Any help would be great any suggestions on how to smooth this out. He says I just need to run it. The motor is on a 15' ski boat that i will run tomorrow. It's only run 5 times since the rebuild. thanks tommy

 

[ezeke]

Re: motor idles rough,smokes,coughs

The 1974 115 requires two things for a good cold start: 300 RPM from a good starter with powerful fully charged battery; and chokes that are 100% fully closed while cranking the engine.

You have to take the air silencer cover off the carburetors and watch while the choke plates are closed to make absolutely sure that the plates stay closed completely while the engine is being cranked, and that they release fully when the toggle switch is released.

Some 1974 115 engines came with a form of automatic choke that was later eliminated on the series of motors, if yours is still enabled it would be a good idea to disable it and use the choke switch at the helm for full control of the choke.

The automatic choke was controlled by a temperature switch with wires next to the lifting eye; trace the wires to the terminal block and see if they are still connected.

Be sure that the thermostat (vernatherm) is in place and working properly; it will go a long way towards helping with the smoking and plug fouling. Using synthetic blend oil or full synthetic will help, too.

While you have the air silencer cover of, open the chokes so that you can observe the throttle plates; they need to be 100% synchronized throughout their full range of motion from fully closed at idle through horizontal at WOT. If they are not fully synchronzed, adjust the linkage between the carburetors until they are, following the instructions in your service manual.

 

[countvlad]

Re: motor idles rough,smokes,coughs

Be sure that the thermostat (vernatherm) is in place and working properly; it will go a long way towards helping with the smoking and plug fouling. Using synthetic blend oil or full synthetic will help, too.

also im not 100%positive if you ave it on you motor or not but on my 1989 120 i have recirculation valves on each cilinder.. if they are pluged up it will smoke....

also check the timing at idle.... if its a little off will smoke.... or hard to start

good luck

 

[ezeke]

Re: motor idles rough,smokes,coughs

There are no recirculation valves on any V4 motors in the series 1973-1977 115HP motors.

 

[countvlad]

Re: motor idles rough,smokes,coughs

There are no recirculation valves on any V4 motors in the series 1973-1977 115HP motors.

ok nvm then like ive said wasnt 100% positive... just trying to help a brotha out...

 

[Tommy Miller]

Re: motor idles rough,smokes,coughs

Thanks for the info. I know the choke valves are closing all the way and the throttle plates are working like they should. Where is the T stat and how do i check it. I think the auto choke system is wire for manual operation now. I am using cheap oil and can change to see. I am more concerned about the coughing and sputtering. Could this be a fuel air mixture problem how can i fix. Also I live in very humid south georgia. Would this play a part too.

 

[countvlad]

Re: motor idles rough,smokes,coughs

Thanks for the info. I know the choke valves are closing all the way and the throttle plates are working like they should. Where is the T stat and how do i check it. I think the auto choke system is wire for manual operation now. I am using cheap oil and can change to see. I am more concerned about the coughing and sputtering. Could this be a fuel air mixture problem how can i fix. Also I live in very humid south georgia. Would this play a part too.

"T stat" its the thermostat... you need to get a owners manual or repair manual .... i looked on the motors diagram on johnsons website but i cant seem to find the tstats... if you find them and ou wanna check them you need a pot with water and a thermometer.... bring the water to a boil and observer when they open... i guess first you need to find out whats the temp they open.... its very possible that if they failed, usually open, your motor never reaches optimum temperature and that also explains the rough idle....


you have to make sure the timing is right, carbs are not dirty.. if it runs fine at wot your low flow jets/idle jets might be clogged up... run sone decarb cleaner, SEAFOAM, through the carbs and see if helps... follow the instrctions provided in the repair/maintenence section....

i dont really think humidity is a factor.. you have other issues here.... have you done a compression check?

i know its not easy, and things wont get fixed over night.. have pacience.. let us know....

 

[ezeke]

Re: motor idles rough,smokes,coughs

The thermostat is in the housing centered below the cylinder heads. The two large hoses lead to the housing.

Get the gaskets before you open it up. It's a bit of a challenge if it has not been done in recent years.

Click the thumbnail, please.