1975 johnson 115 won't idle

[buddyholly]

Have a '75 115, it starts fine but when lowering to normal idle it slows down til it finally dies. choking when it is doing this doesn't keep it from stopping, but when choking it, rpms. will jump sharply for an instant then will kill. I have replaced needles and seats, new bulb and installed a clear inline filter before the bulb because there is no filter in the tank on the bottom of the dip tube. when running the filter does not fill up with gas, but at Wot the motor runs really well, but at lower speeds it kind of surges and lowering even further it will fade out and die. Have also taken the pump apart every thing looks good. The only thing that I haven't replaced is the pump and the fuel lines under the hood. If I replace the fuel pump do they still make a kit for it and if not will another pump fit. the numbers on the back of the pump are 318374. Help I am ata loss here.

 

[newtong_ware]

Re: 1975 johnson 115 won't idle

I have a '76 115 (currently rebuilding) and chased this same problem for a while. It is very important to put good fuel line that will seal properly at every location. Even small leaks will suck air it seems, or cause leaks. I took the carbs apart and blew them out and it seemed to work for a brief period, but started screwing up again. Finally I heeded the advice of so many of the guys here and actually ordered a rebuild kit. When I tore them down, in the lower carb I had some fibrous looking stuff just where the brass fitting comes into the carb. cleaned that out, put in the rebuild kit and that fixed it. At least that problem, turned out I had some others. By the way, good thing to remember on these engines, if you ain't sure about the water pump, REBUILD IT!

Good Luck.

 

[tashasdaddy]

Re: 1975 johnson 115 won't idle

did you remove the core plug on top of the carb, and clean the idle jets. did you remove the highspeed jets, have you done a linc n sinc and adjusted the idle speed according to manual?

 

[quinton]

Re: 1975 johnson 115 won't idle

Good Morning i have 1978 115 johnson i let the engine sit on the hydralic for a week and did not rest the weight on the resting arms so i bled the system to let pressure out and now its down and wont manually go back up when in hand lift what did i do? thanx q

 

[tashasdaddy]

Re: 1975 johnson 115 won't idle

Quinton, start your own thread.

 

[buddyholly]

Re: 1975 johnson 115 won't idle

replaced the fuel pump and all new hoses and clamps. took carbs apart and cleaned low idle jets with single strand wire and cleaned the four holes in the botom of the throat of the carbs with carb cleaner and bloew out with air. it still runs rough at idle and runs good at wot. at idle I pulled off each plug wire one at a time and it is firing on al four cylinders. is there a possibility that there is a slight restriction in the idle circuit. can they be cleaned without removing the carbs from the motor by just pulling the jet plugs and spraying cleaner and air thru the oriface?

 

[iwombat]

Re: 1975 johnson 115 won't idle

You might be able to clean them that way, but honestly I think you'll have better luck super-seafoaming some fuel and running it through (1 can: 1 gal). Let it sit and run some more through a day or two later. If you've got something still gumming it up a little that'll probably do the trick. What's the compression numbers on this motor by the way?

 

[tashasdaddy]

Re: 1975 johnson 115 won't idle

i don't like spraying carb cleaner into a mounted carb, as it goes into the engine and strips the lubricant off everything, end up with a dry engine until the lube builds back up.

 

[buddyholly]

Re: 1975 johnson 115 won't idle

The compression is 120psi on all cylinders. my carbs have a push in plug in side the bowl that I didnt remove when rebuilding. is it a must to remove this? is it a reason that it would run bad at low speed? I put fresh gas in the tank before starting all this. and flushed out everything. at idle it just seems to be missing. it shakes the boat, i dont have a tach so i dont know exactly how fast its running, but I know it should be smooth running. and it has to be choked to start every time even when its warmed up. is this normal.

 

[burroak]

Re: 1975 johnson 115 won't idle

The compression is 120psi on all cylinders. my carbs have a push in plug in side the bowl that I didnt remove when rebuilding. is it a must to remove this? is it a reason that it would run bad at low speed? I put fresh gas in the tank before starting all this. and flushed out everything. at idle it just seems to be missing. it shakes the boat, i dont have a tach so i dont know exactly how fast its running, but I know it should be smooth running. and it has to be choked to start every time even when its warmed up. is this normal.

Have you adjusted the slow speed idle? Turn the screw in some and see if it makes a difference. If the screw is down tight, back off the plastic foot with pliers and a screwdriver. Do this while the motor is in the water. You may get more rpm's that your wallet can or wants to afford.

 

[buddyholly]

Re: 1975 johnson 115 won't idle

yeah. I have adjusted the ilde setting, the only thing it does is raise the rpms but it doent make it run any better until it gets going so fast then the high speed jets open up.

 

[hoeser]

Re: 1975 johnson 115 won't idle

It's not normal to need to choke a warm healthy crossflow V4. Mine starts about a half second after turning the key when its warm, no warmup lever, no primer.

 

[burroak]

Re: 1975 johnson 115 won't idle

yeah. I have adjusted the ilde setting, the only thing it does is raise the rpms but it doent make it run any better until it gets going so fast then the high speed jets open up.

I was addressing the choke on the start issue only. If it requires the choke to start when warm, I suspect it is a lack of fuel. Get it to start, when warm, without the choke and then work on the rough idle. Getting it to start without the choke is a step forward.

 

[tashasdaddy]

Re: 1975 johnson 115 won't idle

# 40 is the idle jet in the carb, # 33 is the high speed jet. did you remove these with the special tool? are you sure you have good spark on all cylinders. clik on picture to enlarge.

 

[ezeke]

Re: 1975 johnson 115 won't idle

If you want to run carb cleaner through the idle jets one at a time, there is no good reason not to; you can't run the engine with the orifice plugs out anyway. The jets lead to small capillaries that enter on the floor of the carburetor throats just after the throttle plates.

If you don't run the engine, the Gumout will have evaporated before you run the engine and the capillaries will be clean along with the jets. Just insert the tube rhat comes with the cleaner far enough to make contact with the jets' openings. If you open the choke and throttle plates, you can look down the barrels and see if the fluid is coming through all of the openings. Wear eye shields when working with the aerosol cleaner.

If you take the jets out, soak the carburetors first because if the jets have never been removed they are very likely to be firmly stuck after 30+ years. Finding a matched set of replacement carburetors can be difficult.​

 

[buddyholly]

Re: 1975 johnson 115 won't idle

what is under the pressed in 1/2" plugs that r in the bowls? Idon't want to remove them if I shouldn't or it is not needed. could they be the reason it is not idling good. I haven't done any more to it since the morning of the 4th and won't be able to until 9th since I work the weekend and the boat is in theslip at the marina.

 

[burroak]

Re: 1975 johnson 115 won't idle

replaced the fuel pump and all new hoses and clamps. took carbs apart and cleaned low idle jets with single strand wire and cleaned the four holes in the botom of the throat of the carbs with carb cleaner and bloew out with air. it still runs rough at idle and runs good at wot. at idle I pulled off each plug wire one at a time and it is firing on al four cylinders. is there a possibility that there is a slight restriction in the idle circuit. can they be cleaned without removing the carbs from the motor by just pulling the jet plugs and spraying cleaner and air thru the oriface?

I don't know if it makes any difference now, but when you clean slow speed idle jets a No. 68 drill (.031) is what you should use. A single strand of wire is rather imprecise for such a delicate operation.

 

[buddyholly]

Re: 1975 johnson 115 won't idle

went down and pulled the carbsoff and brought home and disassembled them. this time I removed the four half inch pressed in plugs that r under the idle circuits and found a small amount of trash in there. Ive never had these out before so I didnt know what I would find, if anything. cleaned the rest of carbs again and now I am heading back to the boat to reinstall and to find out if this was the coulprit of my idling issues. I will post my findings.

 

[buddyholly]

Re: 1975 johnson 115 won't idle

motor runs well now even at low idle. I dont have a tach so i have no way to set the idle speed, i would guess about 900rpm tho. the only problem i have is when i put it in gear tied to the dock at idle it wants to slowlly die. have to raise idle to about 1500 to keep running. I have the motor on a 24ft pontoon and the prop on the motor is 17 pitch i think. would this be the reason it wants to die at low idle in gear? the throttle response is good and it runs well for a 32 yr old motor.

 

[iwombat]

Re: 1975 johnson 115 won't idle

It's more likely you've got a fuel delivery issue. Either an air leak, fuel restriction, anti-siphon valve problem, or a fuel pump that's ready for a rebuild.

When it starts to die, try pumping the bulb. If that keeps it going, you'll know for sure.


Edit: Could also be water in the fuel.