1975 115hp Johnson won't idle

[nickscarpinato]

I think I'll just pull my hair out. I have checked the coils with a scope - good shape no loss of fire at any RPM. Replaced the fuel pump, all the fuel hoses, cleaned the carbs twice, including removing the jets and blowing out all the passages and trying slightly different float settings. Adjusted the timing to factory specs. Sprayed oil around the case center joint to see if it was leaking no visable leak, no change in RPM. I just cant get this thing to run below 1500 RPM and it is just a disaster trying to handle it at the dock. I normally paddle in. And compression ranges from 110 to 115. Don't know what to check next. Help Help

 

[J Clarke]

Re: 1975 115hp Johnson won't idle

Did this problem happen during use?, Or has it been sitting around for a few years?. If there is a adjustable idle mixture needle turn it counter clockwise to make it richer for more fuel. If you don't have a service manual try your local public library. Hope this helps .

 

[Joe Reeves]

Re: 1975 115hp Johnson won't idle

Nscarpi.... You don't say what happens below 1500 rpm. Is it a case whereas the throttle handle is at the neutral/idle position but the rpms stay at 1500 rpm, or does the engine die out if you attempt to drop down under 1500 rpm?

 

[nickscarpinato]

Re: 1975 115hp Johnson won't idle

Well there is no adjustment screw, the service manual doesn't say anything about it not idleing, and it was this way when I got it last year. The person I bought it from told me he used it often. I believe that was one of the many lies he told me. By the way I also put new plugs in it, no change.

 

[nickscarpinato]

Re: 1975 115hp Johnson won't idle

Under 1500 it will die out, sometimes I can get it to run at about 1200 for 30 seconds or so. I am running in a tank so that the back pressure is as if it is in the water. This is in neutral I can get it to stay running in gear at 1200 to 1500 RPM but I have to bring the idle speed to about 2500 to do so.

 

[rmpenton]

Re: 1975 115hp Johnson won't idle

i had the same problem with my 77 johnson 115.i had a small leak in a head gasket,but it wouldnt show up on a compression test.i found it becuase i pulled the head off one day and saw the leak in the head gasket.now it runs great

 

[Joe Reeves]

Re: 1975 115hp Johnson won't idle

Nscarpi..... The compression on that engine should be in the range of 100+ psi and even on all cylinders. The spark (with the s/plugs removed) should jump a 7/16" gap on all cylinders with a strong blue flame.<br /><br />The spark plugs should be Champion QL77JC4 or L77JC4 plugs, gapped at .040 .<br /><br />Assuming the above are as they should be, I would look at the following areas.<br /><br />Possibly you have overlooked something in the carburetors (it happens). If those carburetors have a small brass tube within the larger brass high speed nozzle, that small tube is a slow speed passageway that is clogged easily.<br /><br />The linkage connecting the carburetor throttle arms may be improperly adjusted whereas at idle, one of the throttles is still open somewhat.<br /><br />The cam to carb roller (synchronization) is not aligned properly. The throttle should just start to open when the scribe mark on the cam aligns perfectly with the center of the roller.<br /><br />The flywheel.... Usually, if the flywheel key shears even slightly, the engine will not run. However, recently I have come across one engine that would run with the key slightly sheared. It may be possible that you have a problem of this nature.<br /><br />If you have had the flywheel off and upon re-installing it, did not torque it properly, the key could shear. It's something worth looking at. The flywheel nut must be torqued to exactly 105 foot pounds.<br /><br />Let us know what you find.

 

[J Clarke]

Re: 1975 115hp Johnson won't idle

Nscarpi<br /><br /> I would also check to see if any of the reed valves are chiped or broken. Located behind the carbs.

 

[sparkroost]

Re: 1975 115hp Johnson won't idle

I had a similar problem and it was the linkage from carb to carb. If your plastic holders are wallowed or loose, the bottom carb. will not start to open when the upper one starts to open. This will cause an uneven mixture in the lower 2 cyls vs. the upper 2. this will cause the lower cyls to fight with the upper ones.<br />you can eliminate this by going to your local hobbie store for RC cars/boats and such and getting a turnbuckle(one side is fwd threaded and the other is reverse) and the posts and ends for the turnbuckle. You can then adjust the top to bottom synkronization by turning the turnbuckle.<br /><br />You may also want to inspect the reeds. They are valves and need to close and open. They should be closed at all times unless the engine is sucking them open.

 

[nickscarpinato]

Re: 1975 115hp Johnson won't idle

Well: here's what I've done so far, The spark plugs are correct, carb linkage OK, pulled the intake checked the reed valves all look good not bent, chipped, or cracked. I did a cylinder leakage test and found that I had noticeable leakage between 1 and 3. So I,m going to pull the head. I have not had the flywheel off, but I did check for TDC the timing mark lines up where it should be when #1 is at TDC. I went through the complete procedure for carb linkage adjustment, so I'm sure that's OK.<br /> Thanks for your help

 

[SCO]

Re: 1975 115hp Johnson won't idle

how did you do the leakage test?

 

[Solittle]

Re: 1975 115hp Johnson won't idle

Have you checked the thermostats? If removed the motor will not get up to operating temp & may die in neutral. Went through same problem last year with my OMC V4s.

 

[nickscarpinato]

Re: 1975 115hp Johnson won't idle

I brought the piston that I was going to test to TDC and secured the flywheel. Then I used an adapter I have that screws into the spark plug hole to connect an air hose. Brought it up to 110 lbs. and watched and listened.

 

[SCO]

Re: 1975 115hp Johnson won't idle

I am doing the same as you with a 73Johnson 135 for my to date unsolvable idle/start problems.One cyl has less pressure but local mechanics told me no problem. I've always been afraid to remove the heads, for fear of breaking the bolts. Have you done this yet? Howd it go? I would be interested in the torque required to get the bolts to loosen. Thanks