Johnson 140hp WOT problem...

[Jonezy Hick]

I have a 1987 140hp johnson that stalls at WOT. At 2500rpm it starts to sputter then bogs down when I advance the throttle. This is a new engine for me and I do not have a valid history. I have:

replaced the fuel, fuel fiter, fuel lines

de-cardonized the engine using sea foam

rebuilt the carburators

replaced spark plugs

compression is 130/90/120/130


I am hoping that 90psi cylinder is not my issue but I am not hopeful. If it is what are my options? I am mechanically inclined and have friends that are backyard mechanics that can help. Thanks for your input.

-Jones

 

[fireman57]

Re: Johnson 140hp WOT problem...

The 90 is not a good reading as your cylinders should be within 10% of each other. Do a spark check when it bogs and make sure that you are not dropping spark to a cylinder or two at that point. A timing light will tell you. If you lose spark then physically swap coils and see if the problem follows, if it does then you can just replace the offending coil. Pull the plugs and make sure that there is no white goo on them indicating water in that cylinder. You might just need a head gasket.

 

[Jonezy Hick]

Re: Johnson 140hp WOT problem...

I swapped out all four of the coils and spark plugs (not necessary but I didn't want to leave anything to Murphy's Law). I took the boat out last weekend and I am still having the same problem.

The spark looked fine and the plugs are a little on the black side but not terrible. I can reach 5,000 rpm when I am not in gear/under load.

any suggestions on my next course of action?

-Jones

 

[fireman57]

Re: Johnson 140hp WOT problem...

Take a buddy with you and when it bogs have him pump the primer bulb. If it picks up and runs correctly then you have a weak fuel pump. when you rebuilt the carbs did you run a small wire thru all the orafices and jets? If you didn't then you still might have some crud in an intermediate or high speed jet.

 

[Jonezy Hick]

Re: Johnson 140hp WOT problem...

I did run a wire and compressed air through all the orfices I could and used TONS of carb cleaner. I will try the pumping buddy method next time I take the boat out.

Thanks,

-Jones

 

[Jonezy Hick]

Re: Johnson 140hp WOT problem...

took the boat out last weekend and performed the "pump buddy method" with no change. The engine did flood and "sneezed" a few time when I tried to restart it.

I am seriously thinking about re-powering to a smaller engine. 140hp is way too much for my 1976 starlight 27'.

Thanks for the help

Jones

 

[fireman57]

Re: Johnson 140hp WOT problem...

Are you positive that it is not overheating and shorting out a bank or coils to keep it from exploding?

 

[Jonezy Hick]

Re: Johnson 140hp WOT problem...

The pee stream is warm but not hot and you can touch anything (accept the fly wheel of course) on the engine without burning yourself.

 

[fireman57]

Re: Johnson 140hp WOT problem...

I found out on my '78 75hp that the overheat alarm, which was not hooked to a buzzer, was shorting out the top cylinder and making it do exactly what you describe. Not saying that yours is doing that but you might want to disconnect the tan wire from the thermostat and see if it makes a difference. If it doesn't then make sure you hook it back up. If it does then you need to change the sensor. One other thing you might try to help diagnose the problem is when it starts to bog push the key in. this will activate the primer solenoid and shoot fuel into the cylinders. If it picks up we know it is a fuel problem not electrical.