Coughing, Sputtering 1990 25HP Johnson

[Jon Boat Jim]

My 1990 TJ25ELESE 25 HP Johnson is suddenly coughing and dieing. It starts fine, idles OK (a little rough) but when I increase the throttle it coughs and quits running. I limped back to the dock at idle speed yesterday.
Today I checked the plugs (OK) and compression (OK). Then I switched to a new gas line that I knew was OK and then changed out to a different gas tank. Nothing helped. I also inspected the fuel pump screen to see if it was blocked (it appeared to be OK).
The motor just will not run when I try to open up the throttle.... a big cough and it quits running.
My shade tree mechanic diagnosis is that the problem has to do with the high speed orifice/jet. Do you agree?
Can the orifice be accessed without taking the carburetor off?

 

[oldcatamount]

Re: Coughing, Sputtering 1990 25HP Johnson

Could be a couple of things. First, (if you have an induction timinig light), start the motor and see if both cylinders are firing. You can also check the cylinders by removing a plug wire (with motor running, using a pair of insulated pliers to see the reaction of the motor. Do this one wire at a time and see if it makes any difference in the motor. A weak or missing cylinder will create the symptoms you have described. If both cylinders are firing, then it looks like you need to do a carb cleaning/re-build.

 

[Cofe]

Re: Coughing, Sputtering 1990 25HP Johnson

You will have either a plug, or fuel inlet nipple on the front of the lower portion of the carb bowl. The high speed jet is just behind that. Use a single strand of copper electric wire, or some other small wire, and clean out that jet. You may get lucky......

 

[Jon Boat Jim]

Re: Coughing, Sputtering 1990 25HP Johnson

Thank you for the reply USCGO #1172938 and thank you for your service to our country. I will try the plug wire removal method (I knew that I shouldn't have taken that old timing light to the Goodwill!)
From the carb schematic it looks like the High Speed Orifice can easily be accessed from the front of the carburetor. Would it be helpful to remove it and try to run a wire through it, maybe spray some carb cleaner through it?

 

[Jon Boat Jim]

Re: Coughing, Sputtering 1990 25HP Johnson

Lt. Cofe, Thank you for your input. Is the orifice "Part #22 in the parts diagram?

 

[Cofe]

Re: Coughing, Sputtering 1990 25HP Johnson

Yes
If you plan on removing it, do not use a regular screwdriver. You can get a jet screwdriver at a auto parts store, or make your own from a old flat blade screwdriver by grinding it square to fit uniformly in the jet ears. If you break a ear, the jet will have to be replaced. A broken jet ear will make turbulence that will affect jet performance.

 

[Jon Boat Jim]

Re: Coughing, Sputtering 1990 25HP Johnson

Thank you for the warning. However, this is one of the few instances where I have the right tool!