90 HP Johnson problem

[wordmaster]

Hi Y'all,<br /><br />I have an 82 model Johnson V4 90 HP with an idling problem. Here is the background. Every time I have run it up til this weekend, it has performed flawlessly.<br /><br />When I first started this weekend I noticed the tach seemed to be off. In the interest of not taking chances, I kept it below 5000 or so, but it seemed to be slower than that and had plenty of throttle left. Norm is wound out at 5200. This became better the more I ran it and after a while was back to normal, wound out at 5200.<br /><br />Everything smooth, I ran it across the lake and stopped at a marina. While pulling in to the dock, the motor died while idling. After that, it would idle very slow and rough and more times than not, die while idling.<br /><br />I can hear a miss at low speeds up to about 2500-3000 rpm, then it smooths out. at 4000 and above, it is as strong and smooth as ever.<br /><br />I changed plugs, (the quick and easy thing) and visually checked for obvious problems, the plugs made no difference.<br /><br />I cranked it and pulled each plug wire. the top one on the side away from the starter made no difference whether the wire was on or off. I pulled that plug, put it in the wire, cranked the motor, grounded the plug and it is firing very nicely. Looked inside the cylinder with a light, no obvious problems showing there. Is it safe to assume that the top and bottom coils hook to the top and bottom plugs respectively?<br /><br />Would the tach being wrong shed any light on the problem? What would be the most likely things that I could check?<br /><br />Any help would be greatly appreciated. Thank you in advance.<br /><br />OK, I pulled the wire from the plug in the "bad" cylinder and stuck a screwdriver in it. I cranked the motor and got a nice blue-white spark that went well over 1/2 inch, guestimate close to 3/4 inch between the screwdriver and the block. Spark was also jumping from the plug wire boot out to the insulated pliers I held it with to insert the screwdriver. <br /><br />Running in the dark though, with all wires hooked up I did not see any sparks jumping to indicate a problem with leaky wires.<br /><br />I hope to have a compression guage tomorrow, but what else can I try? <br /><br />Perry

 

[OBJ]

Re: 90 HP Johnson problem

Hi Perry.<br /><br />When you pulled the plug wires, was the engine running and it made no difference? Wasn't sure about this part of the post.<br /><br />Just a couple things.....When it starts to miss, pull the plug wires one by one and see if any makes any difference. When you find the one that dosen't make any difference, that's the bad guy. Maybe a coil starting south. Also, try running at night with the hood off and look for any stray sparking going on.<br /><br />Run some fuel system cleaner in the gas like Bomby's 2+4 or Sea Foam. May be just some stuff in the carb.<br /><br />I would suspect an ignition problem though just from your post.<br /><br />Do you know when the carbs wer overhauled last?

 

[wordmaster]

Re: 90 HP Johnson problem

Yes, I pulled the wires while the motor was running the top cylinder on the side away from the starter was the "bad guy". I pulled that plug and checked for spark. There was a nice fat blue spark there.<br /><br />I don't know about the carbs, probably about two years ago. I have run in the dark and saw no sparks. Also, I ran cleaner about two tanks back. I usually do this about twice a year.

 

[OBJ]

Re: 90 HP Johnson problem

You may see the spark but is it hot enough?<br /><br />Heres a quick way to find out. Pull the #1 spark plug wire. Find something to fit in the end that goes onto the spark plug. A nail will sometimes work. Hold the wire with insulated pliers and hold the nail about 1/2" from a clean engine ground. Have someone crank the motor. If you get a hot white strong spark, it's good. All the wires on your engine should do this.<br /><br />For your reference.....<br /><br />Standing in back of the engine, the cylinders on the right (starboard) are the odd cylinders, 1 & 3. The cylinders on the left (port) are even, 2 & 4.

 

[kreecher]

Re: 90 HP Johnson problem

I would also recommend that you wear a good pair of insulated gloves. Believe me when I say you can get a nasty little shock if not paying attention.

 

[wordmaster]

Re: 90 HP Johnson problem

Judging from that, the top cylinder on the right side, looking at the back would be the #1 cylinder?<br /><br />That is the one with a problem. I will try the nail and let you know. Are the coils supposed to be top coil to top plug and bottom coil to bottom plug? Thank you for your help. Any and all ideas greatly appreciated.

 

[OBJ]

Re: 90 HP Johnson problem

You got it wizard....top right cylinder is #1. Coils are mounted the same way.

 

[wordmaster]

Re: 90 HP Johnson problem

OK, I pulled the wire from the plug in the "bad" cylinder and stuck a screwdriver in it. I cranked the motor and got a nice blue-white spark that went well over 1/2 inch, guestimate close to 3/4 inch between the screwdriver and the block. Spark was also jumping from the plug wire boot out to the insulated pliers I held it with to insert the screwdriver.<br /><br />Running in the dark though, with all wires hooked up I did not see any sparks jumping to indicate a problem with leaky wires.<br /><br />And of course, it runs smooth and powerful at higher rpms. What can I try next? Thank you...

 

[whofan]

Re: 90 HP Johnson problem

A guy I work with has a 90. His motor started to loose power gradually over time then it finally gave out, he found out the power pack went bad. His motor is a 99 Johnson 90. At first it wasnt a total failer.

 

[wordmaster]

Re: 90 HP Johnson problem

Mine has not lost any power at all at higher rpm's. It will plane out (24 foot pontoon) and will go with WOT at 5200 rpm like it always has. It is just at low rpm's that there is a problem...under 2500-3000 or so. I'm not sure, and someone can probably tell me, but if the power pack was bad or weak, I don't think I would get the excellent spark that I get at an idle.

 

[wordmaster]

Re: 90 HP Johnson problem

Well, I checked the compression today and here is what I got: <br />#1, the bad one, 45 <br />#2, 130<br />#3, 125<br />#4, 128<br /><br />After spraying some oil in #1, it showed 55<br /><br />Any idea what might cause this, especially considering that the motor is smooth and has full power at higher rpm's? Thank you for any and all comments and help.

 

[DJ]

Re: 90 HP Johnson problem

At best, a bad head gasket.<br /><br />Otherwise, it has to come apart.

 

[OBJ]

Re: 90 HP Johnson problem

Sorry to hear about this one Web. As DJ said, at best a bad head gasket. Take the head off and look at the cylinder. If you see any places on the cylinder walls that have been "wiped", that's usually a sign of that cylinder running lean which would go back to the carb, most likely.<br /><br />On another chance, look for stuck rings. <br /><br />Ya' won't know till it's opened up. Hope for the best....prepare for the worst.<br /><br />Keep us posted as to what ya' find....thanks.

 

[wordmaster]

Re: 90 HP Johnson problem

Thank you for the info. I have a few more questions if you would be kind enough to answer. I know very little about the inner workings of a 2 cycle engine, but if this were a 4 cycle, I would suspect a valve problem. Is this not the case with a 2 cycle?<br /><br />Also, I do not really know enough about outboard engines to tear this critter down and my recreation budget is too strained to afford a pro to work on it for the time being. Will it hurt the motor to go ahead and run it as it is? I will have some docking and trolling problems, but above 3000 or so it still runs nicely. Please let me know on this. Thank you

 

[OBJ]

Re: 90 HP Johnson problem

Web...the only thing that's going to happen is, is it's going to get worse. You tear into yourself and you'll save a lot of $'s, not only by doing it yourself, but before any real damage gets done by running it the way it is. <br /><br />Splurge and get OEM manual and read it. It will explain step by step how to do the work....and if ya' get stuck, holler at us. But I sure wouldn't run it like it is.<br /><br />And there are no "valves" in a two stroke like a there is in a 4 stroke. You do have reed valves right in back of the carbs. The let the gas in and keep blowback from coming out the carbs.

 

[wordmaster]

Re: 90 HP Johnson problem

OK, I have a manual on the way. A genuine OEM for this motor, not a multi year, multi engine Seloc or something. In the meantime, it has been mentioned that I might have a blown head gasket. From my experience in pulling heads on cars, I would assume that by the time I get the head off, I WILL have a bad head gasket. Is there any way to tell if the gasket is bad now?<br /><br />Also, if it is a bad head gasket, where could it be broken to cause the problems I am having. There is no evidence of water in the cylinder so I assume it is not broken between the cylinder and the water jacket. <br /><br />With both plugs out, the #2 cylinder has compression so I assume it is not broken between the cylinders.<br /><br />There is no evidence of blowby on the outside of the motor so I assume it is not broken between the cylinder and the outside. So where could it be bad in order to cause my problem? Thank you for your help.

 

[DJ]

Re: 90 HP Johnson problem

Wizard,<br /><br />The head gaskets typically fail between the combustion chamber and the water jacket. The evidence is a clean spark plug.<br /><br />As I said before, at best, a bad gasket. Go ahead and pull the head. It is SIMPLE on that engine. You'll know as soon as you get it opened up.<br /><br />If the cylinder is scored, you will completely DESTROY the engine if you continue to run it.

 

[12alohawyatt]

Re: 90 HP Johnson problem

How Two-stroke Engines Work<br /> http://science.howstuffworks.com/two-stroke.htm <br />howstuffworks.com has helped me on a lot of things. Wyatt