1987 Johnson 100 HP 2 stroke bogging at full throttle

[SideW@ys]

I have a 1987 100 HP 2 stroke, 4 cyclinder Johnson that is having trouble maintaining full throttle. Last time I took the boat out the engine would not start, but it had recently rained so I figured that was the root cause of the problem. I pulled off the gasline at the engine and pumped about a half cup of water into a jug before gas started to flow (somehow water finds its way in the tanks). I then pulled off the carbs, drained the water from the bowls, cleaned and reinstalled. The engine idled fine and ran good up to full throttle but after about 10 seconds at full throttle the engine boggs down to a slow idle but picks back up RPMs if you pull back on the throttle (or if left pinned at full throttle will bog, pick back up after about 5 seconds, and then bog again after picking back up speed). It idles fine and runs good at about 75% throttle but for some reason it is getting choked at WOT. Did I somehow mess up the timing/carb adjustments when I pulled the carbs? I also tried an auxilary tank with new gas and still have the same issue. Any thoughts? I would really appreciate it.

John

 

[emdsapmgr]

Re: 1987 Johnson 100 HP 2 stroke bogging at full throttle

Possible you have a weak fuel pump. When the engine starts to bog, have a friend constantly prime the fuel hose bulb. This will force extra fuel into the carb bowls. If the engine runs fine as long as you constantly prime the bulb, the pump may be weak. A weak pump will supply some fuel to the carbs, but perhaps not enough to run sustained full rpm's. When the carb bowl is drained, the engine will slow. Once the bowls refill, the engine will take off for a few seconds or so, then slow once the engine consumes the fuel in the bowl again.

 

[barrettr22]

Re: 1987 Johnson 100 HP 2 stroke bogging at full throttle

i would start off by doing simple things like replace the plugs and you already changed fuel but after being wet your plugs are prob gummed up i would suggest champion plugs they seem to do best in johnsons but it sounds like its starving itself for fuel try cleaning your fuel filter also

 

[SideW@ys]

Re: 1987 Johnson 100 HP 2 stroke bogging at full throttle

Thanks for the replies. I forgot to mention that I had also tried squeezing the primer bulb while running the engine to make sure there wasn't a problem delivering fuel to the carbs and there wasn't. The carbs were definately full and this problem persisted. Any other ideas? I'll try changing out the spark plugs when I go down to the boat next next but I'm not so sure that's the problem since the boat will run great for about 10 seconds. If it were they spark plugs I don't see this being the case. I think I am getting too much fuel for some reason, or possible not enough. Any other ideas?

 

[emdsapmgr]

Re: 1987 Johnson 100 HP 2 stroke bogging at full throttle

There could still be some water in the gas tank. Once you get the boat up on plane, the level of fuel in the tank changes as the running attitude of the boat changes-and subsequently the level of fuel in the tank.

 

[SideW@ys]

Re: 1987 Johnson 100 HP 2 stroke bogging at full throttle

I have tried using a portable gas tank with new gas and have had the same problems. With all of the tests I have performed I feel confident its not a fuel or fuel delivery problem to the carburators. I did take off my carburators and put them back on enough times I could have messed something up in the processs. Maybe the gasket between the carbs and powerhead is damaged allowing air to bypass the venturi and enter directly into the crankshaft without picking up fuel on the way? That still doesn't explain the 10 second delay though. I'm at a loss.

 

[emdsapmgr]

Re: 1987 Johnson 100 HP 2 stroke bogging at full throttle

Have you checked for spark on each plugwire when you have experiencing the problems? An inductive timing light will tell you about the spark to each plug. What position is the red schrader valve in on the primer solenoid?

 

[gus-gus]

Re: 1987 Johnson 100 HP 2 stroke bogging at full throttle

I believe you still have a water issue.

Get as much as you can out of the tank, drain the carbs again, and add isopropyl alcohol to your fuel. This will remove the water, but it also will change how you engine runs since water and alcohol will burn but not the same as gasoline.

Lastly, don't let anymore water get in there.