Idle issues '74 Johnson 115

[jbing81]

Hello Gents,
I'm having a bit of a issue with the idling on my Johnson 115 115ESL74B. To start things off I just had the carbs rebuilt and the compression checks out 128-131 across the board.

Now I'm having a Hell of a time starting this motor, I squeezing the bulb til hard (stays hard once going), choke it, lift the warm up lever and turn the key. It cranks and cranks for some time, then if I get lucky it fires only for a moment. I'll do this about a half a dozen times til it finally fires up and stays running. However after idling for a few minutes it begins to sound as if its missing a little, a hiccup here and another there. Sometimes it manages through them, other times it dies abruptly. But once warm it starts right back up. I did notice when it did miss there was a excess poof of exhaust that came out of the upper exhaust ports.

Once under way on the water the motor runs flawlessly, hit the throttle and it gets up and goes.

If anyone can lend some insight I'd appreciate it, I've attached a link to a video for reference. The first 20 seconds are normal, it acts up towards the end


http://static.photobucket.com/playe...obucket.com/albums/v149/jbing81/VIDEO0011.mp4

 

[Daviet]

Re: Idle issues '74 Johnson 115

The next easiest thing to check is spark, it should be bright blue and jump a 7/16" air gap.
You could also use a timing light to make sure each cylinder is constantly firing at idle.

 

[jbing81]

Re: Idle issues '74 Johnson 115

I'm beginning to wonder if I have too many wraps on my "tiny tach" and I'm receiving a incorrect rpm reading. Because I had the boat up to 41 mph on the gps today and the tach was reading 10,000+ rpm! I know that's impossible so it leads me to believe I'm getting a incorrect rpm reading. I will try taking a few wraps off of the plug wire and see of the rpms drop, if they don't then I will look further into my spark and timing. Try the simple things first, right?

 

[jbing81]

Re: Idle issues '74 Johnson 115

The next easiest thing to check is spark, it should be bright blue and jump a 7/16" air gap.
You could also use a timing light to make sure each cylinder is constantly firing at idle.

I forgot to mention earlier that this motor ran like a top last season before I rebuilt the carbs and replaced the control cables. I must have the throttle cable out of adjustment. We will see.

 

[emdsapmgr]

Re: Idle issues '74 Johnson 115

It's really hard to tell the miss at the end of the video, since the video is pretty jerky,grainy itself. If the engine seems to miss somewhat that may be a "lean sneeze." This is an occasional idle miss every few rpm's. A lean sneeze is only at idle and is a carb issue. The small idle passages in the carb can be clogged with dried fuel, restricting fuel flow (only) at idle-causing the engine to idle lean. This can only be cleaned/corrected by using a carb cleaner like a Gumout type product. Once you crack the throttle even slightly, other jets take over and supply fuel. It may run just fine at all rpm's just above idle. You may need to pull the carbs apart and clean the idle passages again in the upper carb bodies. Have you visually checked to see if the carb choke butterflys are closing correctly when the choke is activated?

 

[jbing81]

Re: Idle issues '74 Johnson 115

Well guys i think I mage have found my issue. After messing with the tach I was able to get the rpms in line, but I was still getting a periodic miss. So I started checking for spark issues. Low and behold after removing the coils and having a good look at all four, I found 2 were cracked pretty bad. So with this discovery would it make since that this is the cause of my troubling starts and periodic mis fires?

 

[emdsapmgr]

Re: Idle issues '74 Johnson 115

You can test for good spark with an inductive timing light. Run it on the garden hose. Put the timing light lead on each plugwire while running. The flashes from the gun will show you misfires, nofires and intermittents. You said the engine ran flawlessly once the engine was underway. That does not sound like an ingition problem. Keep in mind that weak ignition components tend to fail once the engine heats up to normal operating temps. Which means it could run fine when the engine is just started (cold.)

 

[jbing81]

Re: Idle issues '74 Johnson 115

I brought the boat to the ramp again today to try and get a better video to bring to the local mechanic. Once again I had one Hell of a time getting it started, but once I did it ran ok for the first 5 min or so then it started missing again. However one thing I did notice this time was even with the warm up lever engaged it still would stumble? If it were a carb idle issue wouldn't it run fine at higher rpms like it did under way?

I'm wondering if I just got lucky last time I was out and for the 10-15 min I just didn't get a miss.

Either way these coils need to be replaced considering they are cracked fairly bad. It that doesn't solve the issue then I guess I will dive back into the carbs and see what I can find.