1977 75hp Johnson Stinger missing?

[edquade]

Hey everyone,

Today while out and about my motor started kinda coughing and sputtering at high rpm's, I was running it for about two hours or so at varying speeds with no problems and then all the sudden flying across the lake it started to cough and then wind back up and cough but went away at lower rpms. I was able to drive fairly slow back to the dock and checked the fuel filter screen, and couldn't see any junk in there. Then later on I fired it up and cruised at low speed for a good 15 minutes before I opened it up and after about 2 minutes at wide open it started coughing again only it didn't go away completely at lower speeds but continually would miss. It never did die completely but would not run very smooth at any speeds at that point. Any possible ideas?

I'm going to go out and see what I'm getting for spark on all three cylinders shortly, would I be wrong in assuming its one of the coil packs? I don't see how a fuel delivery problem could start so abruptly like this. As far as recent electrical work done on it, last summer I replaced the power pack, rectifier, starter, starter solenoid, and battery cables. I have not done anything to the fuel delivery system, I always run premium and try to run the carbs dry after every use.

Any hints or help is greatly appreciated, you guys were a ton of help with my previous issues! Thanks in advance

 

[Bosunsmate]

yes it could be the coils.
do a drop test after that too, see if you can isolate it down to a certain cylinder

 

[edquade]

Okay I'll try that. Thanks, my computer's being goofy and posted this topic 3 seperate times. Sorry bout that.

 

[glenn property of pam]

don't count out fuel as a problem until you have proven its not fuel related. A fuel line blockage or water in the fuel bowl could do the same thing (unless you tried pumping the bulb while you were having these problems and it didn't help). Always better to do the basic compression/spark test first then look at the other possible problems

 

[edquade]

It never crossed my mind to try pumping the bulb while I was on the lake, I did however try two different gas tanks and hoses (both new last July) and neither made a difference. All 3 cylinders had very strong spark, and yielded a drop in rpms when the respective plug wires were pulled off. Is it possible that if it is an electrical problem, that it may only happen once everything is good and warm?

 

[edquade]

Also I should have mentioned that it didn't start quite as nicely as it usually will (both before and during the issues), and it seemed to be lacking power coming getting up on plane. Normally I can throw the throttle ahead and it'll take a little bit to wind up and go but I had to slowly ease into the throttle to keep from killing it. Sometime this week I will try to warm it up good and recheck the spark and also make sure I'm getting fuel.

 

[edquade]

So this evening I fired my boat up for the second time on the plungers with the garden hose, and it ran just fine. Strong spark on all cylinders, so I let it idle for awhile to see if it would start missing when it heated up, however the overheating buzzer started going off and the block seemed to be considerably hotter than normal (I shut it down immediately). After it cooled off I pulled the lower unit off to look at the impeller, which still looked brand new (I replaced it last summer at this time).

Before I put the lower unit back on, is a new impeller housing gasket necessary? What could be a possible cause of it overheating? It also has a new thermostat from this time last year as well, along with a head gasket, and exhaust manifold gaskets.

As far as the original missing problem goes, there is no blockages in the fuel lines, filter, lines from filter to carbs etc. and no water in the carb bowls. Also, judging from the spark plugs all three cylinders seem just fine for fuel.

 

[Bosunsmate]

keep the lu off and hook a hose up to the inlet pipe, that way you can isolate problem to the lu or powerhead/intake pipe

 

[edquade]

Update, there doesn't appear to be any overheating problem. I've had it in the lake twice now, yesterday I ran it for a good 2 hours with zero problems, no ignition problems either, never missed a beat.

Today on the other hand, I ran it for about 45 minutes at a slow pace and then opened it up and it starting missing again. It will only do it under load, after it started at wide open it would do it down to about 1/4 throttle. While it was missing I was able to pull the spark plug wires off and none of them seemed to be the problem, its almost as if its temporarily losing spark to all three cylinders.

I wish I could have posted a video of the issue, but it when its happening at wide open throttle it acts almost as if you pulled the throttle all the way back and then wide open back and forth again and again, at lower rpms its not quite as bad, but at an idle and just off an idle in gear and in neutral it will not act up. I did try pumping the fuel bulb while it was missing and that did not help anything, also the bulb was not spongy or anything.

Is there a specific electrical part that could cause this problem or could there be a wire shorting out somewhere? Would a bad wire going to the ignition switch or the ignition switch itself have anything to do with it? I'm just very confused as to the source of this problem and troubleshooting is very difficult when it only acts up under a load.

 

[racerone]

Run with a timing light hooked up.--Might help in determining where the problem is.

 

[Bosunsmate]

Is there a specific electrical part that could cause this problem or could there be a wire shorting out somewhere? Would a bad wire going to the ignition switch or the ignition switch itself have anything to do with it? I'm just very confused as to the source of this problem and troubleshooting is very difficult when it only acts up under a load.

yes welcome to intermittent fault diagnosis world, hard for doctors too.
you can pull off the red plug in the motor and that will isolate the electrical parts in the controller from being the problem.
you will need to reconnect to kill it.

 

[Bosunsmate]

Is there a specific electrical part that could cause this problem or could there be a wire shorting out somewhere? Would a bad wire going to the ignition switch or the ignition switch itself have anything to do with it? I'm just very confused as to the source of this problem and troubleshooting is very difficult when it only acts up under a load.

yes welcome to intermittent fault diagnosis world, hard for doctors too.
you can pull off the red plug in the motor and that will isolate the electrical parts in the controller from being the problem.
you will need to reconnect to kill it.

 

[Bosunsmate]

Is there a specific electrical part that could cause this problem or could there be a wire shorting out somewhere? Would a bad wire going to the ignition switch or the ignition switch itself have anything to do with it? I'm just very confused as to the source of this problem and troubleshooting is very difficult when it only acts up under a load.

yes welcome to intermittent fault diagnosis world, hard for doctors too.
you can pull off the red plug in the motor and that will isolate the electrical parts in the controller from being the problem.
you will need to reconnect to kill it.

 

[fireman57]

When was the last time you cleaned the carbs. You could have some junk in there clogs the pickup tube momentarily. When it stops sucking fuel at high rpms it clears itself for a bit. With all you have tested I'm leaning toward a fuel problem and the best place to start is with the carbs if you haven't done them in a while.

 

[edquade]

fireman57, I have not cleaned the carbs since I've had this boat which is one year.

So today I got the boat out again finally, fired it up and it was not idling properly immediately, however I took the hood off and wiggled a few wires around on the controller side of the red plug and it started running good. Then took it out, pulled another broken down boat to shore, and took it for about an hour drive of varying speeds from idle to wide open with no issues.

Then when I went to start it back up again, it was clearing not running properly, would not achieve rpms that it normally would by lifting the warming lever up so I began to pull spark plug wires off. Removing the bottom cylinder plug wire appeared to not change the rpms however the other cylinders would change the rpms, all three had spark from what I could tell on the lake. I also unplugged the red plug which did nothing to correct the missing. Pumping the fuel bulb also did nothing. I shut it off as quick as I could after checking all of those things because I assuming the bottom carb had something wrong with it.

Should I just go ahead and rebuild the carbs? Is this a job to tackle at home or would I be better off taking it to a mechanic? I've rebuilt the carb on my 6 hp Evinrude before and multiple tractors but I'm not familiar with trying to synchronize multiple carbs to prevent ruining any one cylinder.

As to the original problem I'm not sure if today's issues were related or not being that the symptoms are completely different.

 

[edquade]

I ended up taking it to a local mechanic, he believes that the charge coils are starting to get weak, he said they test within specs but at an idle started dropping cylinders randomly and sporadically. He put non resistance spark plugs in, cleaned up the sensors (two were covered in rust) and said that it seemed to help. Also the bottom carb gasket had an air leak. Hopefully this will fix my problems.

 

[edquade]

I ended up taking it to a local mechanic, he believes that the charge coils are starting to get weak, he said they test within specs but at an idle started dropping cylinders randomly and sporadically. He put non resistance spark plugs in, cleaned up the sensors (two were covered in rust) and said that it seemed to help. Also the bottom carb gasket had an air leak. Hopefully this will fix my problems.

He also did a compression test, which ended up 127, 120, and 123

 

[geoffwga1]

I think you have been told several times:strip and clean the carbs,it's not hard,just get your digi camera and take a couple of shots of the linkages so you know where to put them back.I had the 76 version of this motor and I was a bit intimidated at first but it's really the same as doing one carb 3 times.It is also something you must eliminate before fooling around with expensive electrics that may be perfectly OK.Oh, and while you have the carbs off get a flashlight and take a look at your reeds but don't disturb them unless something is obviously wrong,Like a screw wedged under one(an issue I had and which ultimately wrecked the motor)..

 

[fireman57]

Sorry I haven't been on in a while. If you were losing spark on one cylinder and you know it because you jiggled wires I would that the harness apart or see if I had a weak or broken connection somewhere. Your coil might be fine just a bad connection. The easiest way to test is to physically swap coils and see if the problem follows it to that cylinder. If it does just replace the bad coil.

 

[edquade]

Forgot to add that the mechanic cleaned the carbs and checked the reed valves, all were fine. He had it on a timing light and determined that it was just randomly missing on all three cylinders. I think the time I wiggled some wires and it started running fine was a fluke, after that I did check out the wiring harnesses and couldn't find any bad spots were it could be shorting. I also unplugged the red plug going to the controller and that didn't change anything while it was acting up. I did take it out to the lake and anything faster than an idle in neutral it would start coughing and wouldn't hardly run in gear. Back to the mechanic I go