acceleration problems

[macorre4]

hi i have a 1990 johnson 100hp commercial vro outboard and the past two times i have gone out with it its been giving me problems it starts up fine idles good takes off with no problems but when i fully accelerate it it runs good for about 2 mins then it slows down for acouple of mins then picks back up it does that back and forth constantly can anyone tell me what this can be or where to start

 

[emdsapmgr]

Re: acceleration problems

Probably a fuel delivery issue. Possible a weak fuel pump. When the engine begins to slow, have someone constantly prime the bulb on the fuel hose. This will force extra fuel into the carbs. If it runs fine at top end while you are constantly priming that bulb, the pump may need to be replaced. Also, could be a bad anti-siphon valve atop the built-in fuel tank, or a bad fuel hose. Any air (or fuel leaks) inside the cowling?

 

[macorre4]

Re: acceleration problems

Probably a fuel delivery issue. Possible a weak fuel pump. When the engine begins to slow, have someone constantly prime the bulb on the fuel hose. This will force extra fuel into the carbs. If it runs fine at top end while you are constantly priming that bulb, the pump may need to be replaced. Also, could be a bad anti-siphon valve atop the built-in fuel tank, or a bad fuel hose. Any air (or fuel leaks) inside the cowling?

we tried the bulb priming and same didnt make a diffference theres no leaks in the cowling but do u think if the fuel line has air that would cause it

 

[macorre4]

Re: acceleration problems

i also noticed that it waisted alot more fuel then normal i also heard those motors have a slow mode do u think that would be the problem

 

[emdsapmgr]

Re: acceleration problems

Likely your fuel pump is ok. Good that you don't see any fuel system leaks. Have you checked your spark when the engine slows down at full throttle? You can use an inductive timing light to check it. The flashes in the gun will show misfires and weak firing. You engine is likely not equipped with SLOW.

 

[macorre4]

Re: acceleration problems

ok ill check that but would air in the fuel line cause that because i checked the 2nd to the last time i went out it was doing the same thing and when i pumped the buld i noitced that the bulb was soft so i disconected the fuel line from the motor and pumped the bulb unilt all the air cam out and connected it back to motor and it ran fine butt the last time i checked and the bulb had pressure and i just check the fuel filter on the motor and noticed it is empty im wondering if there is a fuel leak before the motor

 

[emdsapmgr]

Re: acceleration problems

The fuel hose bulb should get hard when you pump it up. Once the engine runs a while the bulb will get softer. If the bulb collapses when running-that's a problem. It is not unusual for some air to appear in an inline white pastic fuel filter. That's normal. If the filter appears to fill with air only after running, you could have an air leak at the tank fitting or prior to that filter. That's why I asked if the engine ran differently if you constantly primed the fuel hose bulb. Sometimes the rubber oring in the fuel line connectors can leak air-have you tried a different hose from the tank?

 

[macorre4]

Re: acceleration problems

not yet and i think this started after i added a water seperation filter i think that im going to run the line straight from the tank to see how it runs. and would u know what the timing has to be on that motor

 

[emdsapmgr]

Re: acceleration problems

That engine was not made to handle a water separator filter. If you add one, you need to be wary of excess fuel suction through that filter and filter head. Good idea to test without the filter in the line. Check for kinked hoses (fuel restrictions) where they attach to the filter.

 

[macorre4]

Re: acceleration problems

ya i check the lines and they wre fine i believe its the filter ill try it this weekend wiith out it and see

 

[macorre4]

Re: acceleration problems

i went to the lake this weekend and what i did was i disconnected the filter and ran the fuel line straight into a 5 gallon gas container and the engine ran great now i have a question at what rpms is the motor suppose to be running at in idle and at full throttle nad what is the timming suppose to be at and how do i do the timing on it i dont even know what side is the # 1 cylinder is on or whitch on it is

 

[emdsapmgr]

Re: acceleration problems

The engine idle should be set when the boat is floating in the water and it is idling in forward gear: 650 to 750 rpm. You should see 5500 rpm on the tach at wide open throttle. If not, you should consider repropping to get close to this high rpm target. Don't worry about the idle timing, just set it for the rpm. If you are unsure of how to adjust or set the timing, get a factory original service manual from Ken Cook Co., in Milwaukee or: OUTBOARDBOOKS.COM.

 

[macorre4]

Re: acceleration problems

ya thats about what im getting on open throttle thanks for ur help