1990 Johnson 115 Fuel issue?

[tlayman]

My Johnson is acting up but it's symptoms are confusing, the boat is new to me so I've only had it out 3 times. It runs good when I first take it out, but after it's warm it seems to lose power and won't plane, I've only done this once but I let it cool for about 20 minutes and it ran good again for another 10-15 minutes, speeding up, slowing down, everything I tried. Here's what's stumping me, when it loses power, pushing the key in makes it run better and I can get it out of the water and up to 4500-5000 if I keep occasionally pushing it in. Wouldn't this mean I can rule out a sparking issue? Squeezing the bulb does not help when it's running bad. The only spark test I've done is pull the wires one by one while idling and getting a noticable difference, it idles great by the way. I've replaced plugs & plug wires, and am using brand new gas, compression is good, 120 on all 4. I plan to put carb kits in this weekend. Any thoughts on what else to look for? I appreciate any and all feedback.

 

[tashasdaddy]

Re: 1990 Johnson 115 Fuel issue?

hold off on the carb kits, it sounds like you are either dropping a coil or power pack when the motor warms. when it starts to act up, immediately stop in the water and check spark to all 4 cylinders. if you have spark on all 4 at this point, i would consider carbs. if you are not getting spark to all 4, go to the ramp and swap a good coil for the suspect coil, if the problem follows the coil replace it. if you have 2 coils not firing, suspect that power pack. you have 2 power packs, on for 2 cylinders. also make sure the fuel tank vent is clear. fuel pump cannot suck gas out of a vacuum.

 

[ezeke]

Re: 1990 Johnson 115 Fuel issue?

When you push in the key you add fuel to the fuel/air mix, thus indicating that you are running with either too little gas or too much air. This is called running lean and can be fatal as a lean mix runs too hot and can destroy an engine. Start with a survey of your fuel system searching for air leaks or fuel obstructions.

If you find no problems there, you may need to rebuild your carburetors.

 

[tlayman]

Re: 1990 Johnson 115 Fuel issue?

I'm sure the vent was open, to rule out any problems with my main tank I'm using a portable with a new hose & bulb, both tanks yield the same results. So I know I'm good from the tank to the engine. How do I test for air leaks? I've squeezed the bulb good and tight looking for leaks and don't find any gas leaks.

 

[ezeke]

Re: 1990 Johnson 115 Fuel issue?

Using the portable tank was the best way to exclude possible problems up to the fuel pump. Squeezing the bulb probably gets you past a possible fuel pump problem. If you want to check the electronics, the fastest way is to use a inductive timing light on each wire at speed to see if you are loosing a cylinder at the higher RPM. It is a two man job, but it is quick.

I'm betting on the carburetors.

When you get everything working right, you might want to add a full-sized, water separating fuel filter to your setup.

 

[tlayman]

Re: 1990 Johnson 115 Fuel issue?

I verified spark and then went for the carbs and found plenty of gunk around the high-speed jets. The kits didn't amount to much, I basically cleaned the carbs and replaced the needle & seat. While I was at it I bypassed the oiler and added a water separater, it fit nicely where the oil tank was!! I took her out last weekend and she ran great, thanks for the advice, I answered a lot of questions by reading the archives here. But after running a 25hp Merc for the past 5 years I'm astounded at the fuel consumption. I ran across the lake and back and idled around some, couldn't have been more than 12 miles total, went through about 4 gallons, ouch!

 

[ezeke]

Re: 1990 Johnson 115 Fuel issue?

Thanks for the feedback, I'm sure that it will help others.