Johnson 90 HP (1999) Bogs down

[stkonmyboat]

I recently purchased a boat with a 99 Johnson 90 HP motor. I after going out a couple of times it started to bog down after an hour. I tried to make some changes that I thought would fix it. I emptied and cleaned out the fuel tank. I also changed the filters and plugs. Again went out ran for a hour good then lost power after a hour. Full throttle runs at an idle speed.

I brought it to my mechanic and he checked the carbs and engine compression. All was good. He also checked the fuel pump. He said it was all ok. He did change the thermostat think this was causing it shut down.

I took it out again and it happened again. After a hour it lost power. At full throttle it moves at idle speed.

HELP. I want to enjoy at least 2 hours out on my boat at one time.

Any ideas what can be wrong???

 

[ezeke]

Re: Johnson 90 HP (1999) Bogs down

Have you tried running on portable tanks to eliminate possible tank problems?

 

[ob]

Re: Johnson 90 HP (1999) Bogs down

There are a host of issues that could cause power loss.From intermittent spark loss due to failing powerpack to the engine going into S.L.O.W. mode either because of an overheat condition or a faulty temp sensor.You can either perform a touch check on head covers when engine bogs or they make a 163 degree thermo melt stick for checking various locations on the block.Running temps above 163 F are cause for concern.

 

[tashasdaddy]

Re: Johnson 90 HP (1999) Bogs down

it sounds just like a clog vent on a built in tank. the motor cannot suck fuel out of a vacuum. why i don't know, but critters love to build homes in vent tubes, and tale tell hoses.

the only way to find what is causing this, is trouble shooting, immediately and the time it is acting up. i would take a spark checker and compression guage with me. when it starts to act up. immediately check spark on all 4 plugs. then possibly compression, also check temp.

this little baby comes in really handy. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93983

if you have spark, compression correct, and it is not running hot. you have found you have a fuel delivery problem. vent, air leak, fuel pump, dirty carb clogging, which is extremely dangerous, because no fuel, no lube.