1990 Johnson 150 running (what seems to be) too rich. Any Help is Appreciated

[JustinK96]

Hi Everyone,

I'm posting this for my dad, he's computer illiterate . He bought a 1990 Nitro bass boat a few years ago. When he bought it, it seemed like it was running very poor (it would foul the plugs after just a few hours on the river and it had no power). This is a two stroke so he had disconnected the mechanism that mixes the oil and gas and started mixing it by hand thinking that the mechanism was just dumping too much oil into the mix. My dad took it to a friend that tinkers with boats. He had found that one of the carbs was disconnected (he said the throttle arm or connecting rod came off) so he connected it. He also did a compression test, he said that all cylinders were good (i apologize, I don't have those numbers infront of me). We take it to NY every year to use on the St. Lawrence River, so it's a pain to have to change all 6 spark plugs, every single day that we're there. I've read a bunch of forums and I'm just not having any luck.

So compression is good,
Oil/Gas mix is good,
Spark Plugs are always gapped to spec

I'm wondering if I should start looking at coil packs for each cylinder? Or does anyone have any suggestions for me? Thank you in advance for looking!

 

[Chris1956]

Normally outboards of that year will have fixed high speed jets and adjustable low speed jets. If the carbs are clean, the floats are set to spec and the idle jets are adjusted properly, the motor should run clean.

What is the condition of your motor?

 

[JustinK96]

Thank you for your response, it seems to run great when there's new plugs and we're running full throttle. After we're just "putting" through no wake zones or going slow for long periods of time, it seems like the plugs get fouled. When we pull the old plugs, there were times where it seemed that oil/gas would run out when the plug was removed. I think the engine is actually in really good shape. I'm not sure if anyone has ever adjusted the idle jets.

 

[racerone]

I do not believe there are adjustable idle mixture screws on that motor.----Plugs are well made these days and simply do not need to be replaced every day.-----There is something wrong with the motor.--- ---- Are the thermostats installed and working properly ?----What oil do you use.----And post the compression numbers on this motor.----Does spark jump a gap of 7/16" on all leads , yes or no ?-----I can not see , hear or feel your motor.

 

[JustinK96]

Thank you for your reply, I'm not sure about the thermostats, I'll have to talk with my dad and see if he's ever checked them and will post an update.Same with the compression numbers and oil info. Is there a good way to check the thermostats for good operation besides running the boat? I guess I could remove them and visually inspect them.

 

[JustinK96]

So I have a small update, my dad said he didn't know there were thermostats in this engine, so that may one issue. He said he's been using Quick Silver 2-stroke oil. Still no word on the compression numbers.

 

[racerone]

There is a thermostat at the top of each cylinder head.----Under that wee cover.----Along with a water pressure relief valve.----Those thermostats often fail open.----In the St Lawrence river it would result in a cold motor while idling !----There is no need to replace sparkplugs everyday.----Something is wrong and in my opinion it is easy to determine the problem.

 

[JustinK96]

Just a quick questions, do you think all of the thermostats would need to be defective to be causing the issue?

 

[racerone]

Sorry----It is up to you to do the trouble shooting / inspection to determine why you feel it needs new sparkplugs every day.---That is not normal at all.---I used to troll all day long with a 235 HP Johnson and no problems.