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1995 Johnson 30 Surging

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KB976

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I have a 1995 Johnson 30 HP 2 stroke outboard on my Princecraft. This year it developed a problem that I have yet been able to fix. It runs perfectly fine for about 5 minutes, but then suddenly starts surging hard. If I leave it in neutral, no matter what percent of throttle I give it, it doesn't do this, but as soon as I put it in gear it starts surging. It’s hardly noticeable under a 1/4 throttle, as I get into the throttle more it gets worse. At full throttle it surges hard, and if forced to continue, will start to loose power until it dies. Under 1/4 throttle, I can drive it around and keep going with only a slight surge that does not kill the engine. Thinking it was overheating and this was some sort of limp mode, I replaced the water pump, thermostat, and water temp sensor which did not fix it. So I also replaced all the fuel lines, gas tank seals, primer bulb, and fuel pump. Nothing seems to have fixed it. Pumping the bulb does not change the surging either. The hard part is troubleshooting it. I can’t get it to duplicate the actions in my driveway, it has to be in the water, and has to get complete warmed up before it will do it. This poses a challenge to getting it narrowed down. Also, no warning alarms or bells are sounding.

Any suggestions on what to focus on next or how to resolve this issue?

TIA.
 
You seem to have addressed all the fuel related items except cleaing the carbs. Could be a clogged hi-speed jet. Maybe this will help:
www.crowleymarine.com

SHIFT LINKAGE - 1998 Outboard 50 X50ESLECC | Crowley Marine

View parts diagrams and shop online for SHIFT LINKAGE parts, 1998 Outboard 50 X50ESLECC. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.
www.crowleymarine.com www.crowleymarine.com

Also, it could be a fuel delivery problem to getting fuel into the bowl caused by a needle/seat problem #16 & 17 in the diagram. To fully clean the carb, you'll need to order a carburetor kit and remove the plugs (3 and 4) and clean the small passages under those plugs. The kit will include replacement plugs. Other issues could include poor spark. You can purchase a "spark gap tester" at any large auto parts store and set the gap to about 7/16" and make sure your spark can jump that gap with a good blue spark. If it can, that insures that it will have sufficient spark to provide enough ignition to hande the fuel supply at full throttle. A good test of overall ignition issues is the crank it up with watter supplied and with the cowling off and look for any sparks (arcing) caused by bad wires.
 
Oldsaltydog said:
You seem to have addressed all the fuel related items except cleaing the carbs. Could be a clogged hi-speed jet. Maybe this will help:
www.crowleymarine.com

SHIFT LINKAGE - 1998 Outboard 50 X50ESLECC | Crowley Marine

View parts diagrams and shop online for SHIFT LINKAGE parts, 1998 Outboard 50 X50ESLECC. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.
www.crowleymarine.com www.crowleymarine.com

Also, it could be a fuel delivery problem to getting fuel into the bowl caused by a needle/seat problem #16 & 17 in the diagram. To fully clean the carb, you'll need to order a carburetor kit and remove the plugs (3 and 4) and clean the small passages under those plugs. The kit will include replacement plugs. Other issues could include poor spark. You can purchase a "spark gap tester" at any large auto parts store and set the gap to about 7/16" and make sure your spark can jump that gap with a good blue spark. If it can, that insures that it will have sufficient spark to provide enough ignition to hande the fuel supply at full throttle. A good test of overall ignition issues is the crank it up with watter supplied and with the cowling off and look for any sparks (arcing) caused by bad wires.
Click to expand...
I thought about the carb for a bit, but can’t figure out why it wouldnt start acting up until after it was warmed up. I am in the page of electronics now. I will try to do a spark test as you suggest, but this will be a challenge as it only does it when in drive which means I need to be on a lake while moving for it to happen.
 
What you need is a $10 "Spark Gap Tester" from a good auto parts store. Set the gap at 7/16" and test to make sure the spark is sufficient to jump that gap. Basically, if the spark is strong enough to bridge that gap, it's strong enough to handle the demands of what wide open throttle requires.
 
Oldsaltydog said:
What you need is a $10 "Spark Gap Tester" from a good auto parts store. Set the gap at 7/16" and test to make sure the spark is sufficient to jump that gap. Basically, if the spark is strong enough to bridge that gap, it's strong enough to handle the demands of what wide open throttle requires.
Click to expand...
So I finally got around to testing the soark
Oldsaltydog said:
What you need is a $10 "Spark Gap Tester" from a good auto parts store. Set the gap at 7/16" and test to make sure the spark is sufficient to jump that gap. Basically, if the spark is strong enough to bridge that gap, it's strong enough to handle the demands of what wide open throttle requires.
Click to expand...
I finally got around to testing the spark. Both plugs were able to make a 7/16” jump, the top spark seemed weaker than the bottom, but still was making the jump. I then decided to run the motor with a plug wire off, first the bottom then the top. The motor stayed running with the bottom plug disconnected, from idel to high rpm. The motor would not run at idel with the top plug disconnected, but would run at higher rpm.

Is this an indication of anything?
 
Is the surging instant / abrupt ?----If so then run with a timing light one cylinder at a time.----Observe the flashing of the light.---Perhaps you are loosing spark on one cylinder ?----Post video of this surging as I can not see , feel or hear your motor.
 
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