Idle Issues - 1980 Johnson 115 - J115TLCSA

Jk100585

Recruit
Joined
Jun 6, 2024
Messages
2
My engine is having trouble idling when the warm up lever is lowered to the run position. Not all of the info below is relevant (to my knowledge) to the issue I'm currently having but I figured I would give a detailed background for the sake of being thorough.

I recently purchased a 1980 Johnson 115 (J115TLCSA) with good compression to replace the 1995 J115TLCSA that was on my 1977 Starcraft SS 18'. The 1995 lost power last summer and it was going to be cheaper to buy this used engine than to get that one fixed. I got the 1980 home, replaced the spark plugs and one of the heads that had the threads stripped out of the spark plug hole and voila, it ran great. Smoky, but that's to be expected after soaking it in fogging oil for a couple days. So I preceded to rebuild the carbs, replace the exhaust gaskets, oil seals, air intake gaskets, impeller and housing, thermostats, fuel pump and all hoses , primer pump and all hoses, and the starter solenoid. I got it all put back together and mounted to the boat and after adjusting the throttle and shift cables, it starts easily and runs fairly smoothly when the warm up lever is up but a couple inches before the lever gets down to the run position, it dies. From what I've read, it could be one or more of the following things:

*1. The throttle cable is improperly adjusted
**2. Timing is off
***3. Fuel delivery (carburetors, primer pump or hoses)

*The cables were attached with warm up lever in "Run" position and the throttle trunnion adjustment nuts were tightened until the idle adjustment screw touched the stop.

**When I first got the engine running, it had no issues idling with the warm up lever in the run position. Also, no problems when accelerating or running at higher RPMs when in gear. Could the timing have changed when performing any of the repairs listed above?

***Unfortunately, I feel like this is the most likely culprit. I have seen improvement after each step in the following sequence. Almost everything in the fuel delivery system is new besides the carburetors themselves. The first time rebuilding the carbs, it was starting to storm pretty bad and since it already ran pretty well, I decided not to remove and clean any of the jets or remove and clean beneath the plugs inside. (I also got in a hurry and failed to measure and adjust the new floats) Once mounted on the boat, I couldn't get the engine to start at all so I mixed a new tank of gas and tried again. It would start but only for about 3 seconds and then die like it wasn't getting fuel. So that's when I replaced the primer hoses. It started a little easier but still would not stay running. So I decided to bite the bullet and purchase a new set of rebuild kits for the carbs. This time I took my time and removed the plugs and all the orifices and sprayed carb cleaner through all the passageways, replaced the O-ring on the screw plug for the intermediate speed orifice and the gasket on the screw plug for the high speed orifice. (Now that I'm looking at the parts diagram, I believe the high speed orifice screw plug should also have an O-ring instead of a gasket. I'll change that out tonight but the seal is tight on all of them.) I adjusted the float to hang 1" below the mating surface when in running position and made sure they were level when upside down. After that, the engine started easily and ran well with the warm up lever in the start position but wouldn't tolerate being lowered very much. I noticed the idle screw was not fully against the stop so I adjusted the throttle trunnion adjustment nut to make the idle screw rest against the stop. That improved things greatly but it still dies when the lever is about 2 inches from its lowest point. I will hook up the tach tonight and see what the RPMs are when the engine dies. It seems to be running at a pretty low RPM before it dies like the idle screw needs to be tightened but there isn't enough room left on the screw to adjust it far enough.

Please help!! I wasn't able to get it ready in time for a weekend at the lake with my in-laws and my father in law (a man without a mechanical bone in his body) already thinks this is a foolish endeavor. I have to get it going to, at the very least, prove him wrong. Thanks.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,772
Post the actual compression values here.----Does spark jump a gap of 3/8" on each lead using a proper test device?----Are the model #'s the same on the 1980 and 1995 model as you posted ??----The electric primer is a valve , it is not a pump.----Replace water pump impeller or at least test the overheat horn.
 

Jk100585

Recruit
Joined
Jun 6, 2024
Messages
2
Post the actual compression values here.----Does spark jump a gap of 3/8" on each lead using a proper test device?----Are the model #'s the same on the 1980 and 1995 model as you posted ??----The electric primer is a valve , it is not a pump.----Replace water pump impeller or at least test the overheat horn.
Thanks racerone.
Compression results:

#2 - 135psi #1 - 123psi
#4 - 120psi #3 - 125psi

The overheat horn works but I didn't want to remove the temp switches to test since I already re-assembled the heads.

After I got your response, I decided to go ahead and hook up the tach so I could get rpm readings to post as well. Then everything crumbled...
After hooking the tach up, I couldn't get the engine to fire up. Then with the tach removed, it fired up fine once then wouldn't at all. Tested spark and was only getting spark on cylinder #2. A couple days later it started fine. Thought maybe it was the old tach so I put a new(er) one on. The engine fired right up again but sounded like it was running fast and the tach was reading 8000 rpms so I shut it off and removed that tach. After that, it fired up once more but when I went to test for spark I got nothing. And it wouldn't start again.

Test results:

Resistance between two yellow wires coming from stator:
0 ohms

Resistance between the two pairs of brown wires coming from stator:
Port-568 ohms
SB-552 ohms

Resistance on 4-wire plug from (timer base I think?):
Port Side
D-A,B,C: no continuity
A-B: 32
A-C: 32
B-C: 64

Starboard Side
D-A,B,C: no continuity
A-B: 32
A-C: no continuity
B-C: no continuity

This makes me think that the timer base is bad. I'm pretty sure that's what those 4-wire connectors go to, correct? That would explain it not being able to go into neutral before I made it worse with the tach.

What about the tach would've made a change in that? Could it have already been going bad and whatever load from the tach made it worse?

The engine going on the boat is a 1980 J115TLCSA and the one I removed is a 1995 J115TLEOR. So other than the year, they are the same engine.

Here is a list of everything I've replaced so far:
-Impeller and water pump housing
-Oil seals on prop shaft
-Carb gaskets, float and needle
-Head and cover gaskets
-Spark plugs
-Thermostats
-Coils
-Electric primer valve
-Ignition switch
-Propeller
-Inner exhaust housing seal
-Fuel filter, pump and hoses
-Shift rod cover gasket
-Gearcase fill plug seals
-Airbox gasket
-Starter solenoid

Thanks for your help with this.
 
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