2004 johnson runs great up to 3500 rpm's

[basscat348]

Engine starts fine and runs great up to about 3500 rpms, at that point it feels starved for power and the motor starts to surge alot. This is a new problem and has just came up all at once.The boat is run alot , about 3-4 times per week and really never any major problem until now.After engine sits for an extended period like fishing for an hour this has a hard time starting again like its never been run.

 

[SparkieBoat]

Re: 2004 johnson runs great up to 3500 rpm's

sounds like a fuel problem, is this a fuel injected or carbed motor?? bad fuel connection or pump maybe.

 

[SparkieBoat]

Re: 2004 johnson runs great up to 3500 rpm's

also what HP are we talking about??

 

[basscat348]

Re: 2004 johnson runs great up to 3500 rpm's

It is a carb 115hp

 

[SparkieBoat]

Re: 2004 johnson runs great up to 3500 rpm's

if all fuel lines and the pick-up in the tank and the tank vent all check out sounds like possible fuel pump..try pumping bulb and see if that helps, also test fuel pump by removing spark plugs and fuel line coming out of pump, then pump bulb till fuel reaches it then crank, fuel should shoot out in spurts at a fairly good rate.

 

[basscat348]

Re: 2004 johnson runs great up to 3500 rpm's

ok i checked the vent thats ok and the fuel pick up is clean.I checked the fuel pump like you said by priming fuel up to fuel pump then cranking the engine and no fuel comes out.Fuel will come out by just using the primer bulb.OH another thing i just took the I guess bleed screw out instead of disconnecting one of the hoses,it looked like it would do the same thing.It looks like the fuel pump is about a inch by inch or just a tad bigger is that right?

 

[SparkieBoat]

Re: 2004 johnson runs great up to 3500 rpm's

not sure what model your motor is but here is an example of a fuel pump assembly for a J115GLSRC
http://www.boats.net/parts/search/BRP/JOHNSON/2004/J115GLSRC/FUEL COMPONENTS/parts.html
hose #79 going to the intake manifold would be where to test fuel pump at..you could have problems with a needle valve that would prevent fuel from reaching the carb bowl. I assume that is the bleed screw you are talking about.
fuel pump is part #2 in the diagram. Those puppys are kinda pricey too..it is one of my major complaints about OMC motors, high failure rate and high cost..really unnecessary. they could easily produce one that is better quality and cost half the price..makes me kinda mad but what you gonna do?? invent my own maybe.

 

[lipinski]

Re: 2004 johnson runs great up to 3500 rpm's

Isn't 3500 RPM the point where the safety/failsafe mechanisms cut in? Do you have a check engine light?

for example, I know on my 2003 4-stroke, if I'm in neutral, I can't rev over a certain RPM before the motor does what you describe. I was told that is a safety mechanism.

Supposedly some ECM codes cause the same safety mechanisms to kick in.
Just a thought - I'm obviously no expert....

 

[basscat348]

Re: 2004 johnson runs great up to 3500 rpm's

The bleed screw I was refering to was #32.When squeezing the primer bulb fuel would come out that hole just fine,but when i was cranking the engine over nothing came out.The engine doesnt always cut out 3500rpm just sometimes.Also the fuel filter was replaced 2 weeks ago and very dirty and I checked it today and was even more dirty than last time.Were the fuel hoses in 2004 safe for ethanol use?Could this black stuff the filter is getting be the fuel hoses coming apart?

 

[SparkieBoat]

Re: 2004 johnson runs great up to 3500 rpm's

probably coming from the tank..maybe hoses..sounds like fuel pump to me..