90HP Johnson Running Rough *Pics & Video*

[Stryker23]

Hey guys i currently bought a bass boat with a late 80's 90HP Johnson...ran fine, idled fine and really ran good in the upper RPMs. Well i took it out the other yesterday and it started right up and idles fine but when i give it throttle it sounds like the exhaust has gotten louder if that makes sense? and it doesn't rev as quickly or smoothly..Ive had it out all summer with 0 problems and now its kinda acting weird. The first thing i noticed was the increase exhaust sound..at least that's what it sounds like to me. anyone have any recommendations about where i should start to diagnose it? Ive replaced the plugs. here is a pic of what the plugs looked like on each side of the motor and a video of it running. In the video you can hear it doesent want to rev as high as normal. Click the link below to see the video.thanks!

IMG_0489.mp4 video by atvkid4eva - Photobucket

 

[Daviet]

Re: 90HP Johnson Running Rough *Pics & Video*

I would start by doing a couple of basic checks, spark and compression, easy to do and don't cost anything. Then check the fuel delivery system, fuel lines. connections, filter. Might be time to overhaul the carbs.

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

i am gonna do a spark and compression test this week. Is there any good write ups on how to rebuilt the carbs? ive done many carbs, but never on a two stroke. Thanks,

 

[metriccrescentwrench]

Re: 90HP Johnson Running Rough *Pics & Video*

What plugs are you running, and how long has the current set been in use?

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

they are champions..the stock size. I bought the boat at the beginning of summer and just changed them the other day. I havent had it back out in the water since, but running it on the muffs it still seems sluggish

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

Ran perfect at the beginning of the summer with those old dirty plugs

 

[johnson89]

Re: 90HP Johnson Running Rough *Pics & Video*

it statred doing this after changing the plugs? if so check your plug wires maybe you put the wrong wire on the plugs,its an easy mistake....

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

okay guys i have some news. I ran a compression test and all the cylinders were between 115 and 120 PSI so that is not the issue. I also ran a spark test and the bottom right plug wire barely has any spark at all. So does that mean my coil for that cylinder is bad? That has to be the reason that the motor is being sluggish. Let me know what you guys think. Thanks!

 

[yoster]

Re: 90HP Johnson Running Rough *Pics & Video*

it statred doing this after changing the plugs? if so check your plug wires maybe you put the wrong wire on the plugs,its an easy mistake....

Johonson.. read his post again..
"they are champions..the stock size. I bought the boat at the beginning of summer and just changed them the other day. I havent had it back out in the water since, but running it on the muffs it still seems sluggish"

Particularly the part where he says he hasn't had it back on the water since changing the plugs. He's just saying that he already tried changing them, but on the muffs it still seems like the issue exists.

Stryker - Definitely sounds like you may be only running on 3 cylinders. Before looking at the coil, see if you can check for arcing of the plug wires. You'll probably need to do this at night.. needs to be very very dark to see it. If the wire is arcing against a piece of metal in the engine compartment (common occurrence when the wires need replacing), you'll lost most if not all spark to the plug. Good chance these might be the original wires for the engine, so I'd start there first.

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

I took one of the other wires that was getting spark and put or on that cylinder and got the same weak spark. All te connections looked fine for the wire and the coil. I'm pretty sure the wire is not the problem. Is a bad coil the only other possibility?

 

[Daviet]

Re: 90HP Johnson Running Rough *Pics & Video*

Swap the coils, if the weak spark moves you have a bad coil.

 

[Sprky]

Re: 90HP Johnson Running Rough *Pics & Video*

...........

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

So you saying with a shot of carb cleaner the cylinder shouldn't surge if it is getting the proper fuel supply?

 

[ezmobee]

Re: 90HP Johnson Running Rough *Pics & Video*

Swap the coils, if the weak spark moves you have a bad coil.

I would first do this.

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

I will do this when i get off work tonight. Hope its the coil so i can grab one before the weekend and still fish the bass tourney on Sunday. Ill post back this evening. Thanks!

 

[Sprky]

Re: 90HP Johnson Running Rough *Pics & Video*

..............

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

Would one cylinder not firing correctly cause there to me more blue smoke than normal?

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

I'm pretty sure i found the problem by doing the spark test..the one cylinder has a VERY weak spark.

 

[Stryker23]

Re: 90HP Johnson Running Rough *Pics & Video*

okay so i went to swap the coils and realized that the bottom of the coil was melted a bit and causing the metal on the coil to not contact the motor when mounted. I cleaned up the melted plastic and now it has spark! do the coils ground on the block where they mount?

 

[BonairII]

Re: 90HP Johnson Running Rough *Pics & Video*

Now that you've figured out the problem...probably not a bad idea to order new coils now.