25 HP Johnson Seahorse - Throttle problem

[joeoakes]

Good evening folks. I have a 25 HP seahorse on my riverboat. The motor starts fine and idles fine all day long. When im on the river running near or at full throttle for several minutes the motor suddenly 'chokes' down to less than half throttle and the motor winds up and down repeatedly almost like its running on one cylinder (not sure if it has one or two). Maintenance done on my motor has been several carb overhauls, and spark plug changes. I am at a loss as where I should go next with figuring out this problem. Summertime is here and time to be setting limb lines. Any ideas suggestions are appreciated.

Model Year 98 or 99.

Tank and hose/bulb assembly new and working fine.

Thanks for your help.

Joe

[jethro66]

Hi there,what year is the motor?Did you try priming the bulb while it was running?It might be your fuel pump going.I'm sure the pros will chime in and help you,they helped me!!

[joeoakes]

Yes I tried that but doesn't help the problem. I had thought fuel pump also, but would think fuel pump would either work or not. My motor will run fine at full throttle after starting and warming up. After about 10 minutes or so running wide open, problem starts. I will then run approx 1/3rd throttle for several minutes and motor will start running fine again.

[eavega]

Have you checked your spark plug wires? I had a 10 HP that ran exactly the same way; at full throttle it would bog and surge, bog and surge. It would idle all day long. I was told by some AOMCI guys that might an indicator of a spark plug wire shorting out. It only happened at full throttle b/c the ignition plate movement would stretch the wire and cause the short. Two new spark plug wires later the motor ran like a champ. I don't know if that applies to your motor. Just sharing the experience.

Rgds

-Eric

[rusirius]

Having just went through something similar myself, it sounds to me like the S.L.O.W. is kicking in... It's a circuit designed to limit the RPM's of the engine to 2500 in the event the engine overheats....

First try this... There should be a temp sensor in the head (usually a brown wire coming out of it?). When the motor acts up, unplug that wire and see if it "fixes" it... Don't run it long, just long enough to make sure it goes away when unplugged...

If the problem goes away, then it's definately the S.L.O.W. Then it's time to figure out if the head is actually overheating... Use wax pens or a temp sensor/probe to check the head temp. If it's overheating, then on to figure out why... Impeller? Clogged jets? Deflectors? etc... If it's not overheating, then the temp sensor has probably failed and just needs to be replaced...

FWIW, given the fact that it starts doing it, then goes back to normal for a while would seem to indicate that it IS in fact overheating... Overheats at WOT, then once S.L.O.W. kicks in, it has a chance to cool down and eventually comes back to life...

[R.Johnson]

This is where a service manual is needed. It will have theory of operation on the ignition system. It will tell how to test each component while cranking, or while running. Without the manual, and proper test equipment, you are simply guessing. That can get exspensive in a hurry, plus very frustrating.

[cvtech1]

Please disregard, wrong place.

[14ftgrumman]

Please start a thread of your own, don't be hijacking someone elses.
That is a sure way of how not to get help.
Nor trying to be a smart*****, just the way it is.

[cvtech1]

Sorry guys I just got on and found my tread.

[cvtech1]

Please start a thread of your own, don't be hijacking someone elses.
That is a sure way of how not to get help.
Nor trying to be a smart*****, just the way it is.

No problem just found this site will post my own thread. No offense taken.

[solodiver]

I have a 1969 25 hp Johnson outboard I picked up. It runs well , only it stays at slow speed. It surges and tried to pick up speed.
it will even kick in for a few seconds.

Reading the threads it sounds like my problems may be in the spark plug cable or temp sensor.

[Daviet]

solodiver, you need to start your own thread so we can keep your problem seperate from the others. You need to start with the basics, compression, spark and fuel system. Let us know the results.

[solodiver]

Daviet not trying to be rude, but, who are you to tell me to start my own thread?


My problem is the same type as is discused in this thread. Any information would be helpfull to both