Moves slow

stone71

Cadet
Joined
May 16, 2023
Messages
6
Have a Johnson seahorse 35 Hp , it'll run like new with muffs but soon as I put in water it'll only go maybe 5 mph. Both cylinders firing, carb been cleaned and redone anyone have an answer for me please. Thanks
 

airshot

Vice Admiral
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Jul 22, 2008
Messages
5,084
Is the rpm at wot when in the water?? What type of boat is it on ??
 

racerone

Supreme Mariner
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Dec 28, 2013
Messages
37,826
Model #, pictures or year is helpful.-----Sounds like it might be running on 1 cylinder.-----Check reed valves.---Does spark jump a gap of at least 5/16" on a test device ?----Post compression test values.-----Check flywheel key.-----Check for blocked exhaust housing.
 

stone71

Cadet
Joined
May 16, 2023
Messages
6
Model #, pictures or year is helpful.-----Sounds like it might be running on 1 cylinder.-----Check reed valves.---Does spark jump a gap of at least 5/16" on a test device ?----Post compression test values.-----Check flywheel key.-----Check for blocked exhaust housing.
 

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stone71

Cadet
Joined
May 16, 2023
Messages
6
Not sure of year. Both cylinders fire good. Sounds and runs like new until there's force if water around it. Really appreciate you answering me and trying to help me figure this out.
 

racerone

Supreme Mariner
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Dec 28, 2013
Messages
37,826
A 1982 model.-----They sound good to the untrained ear , when running on a hose.----Not making enuff power to push a boat.-----Should be easy to figure out.----Perhaps flooding.----Fuel pump diaphragm ruptured ??----Nozzle gasket missing?----High speed jet inside the carburetor bowl plugged.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,826
Sounds like it is running on 1 cylinder.-----I can not see , feel or hear your motor.-----Trouble shooting must be done by you.-------Remove top plug wire.----Try and start the motor.-----Repeat with removing only the bottom plug wire.
 

Bob_VT

Moderator & Unofficial iBoats Historian
Staff member
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May 19, 2001
Messages
26,046
Another way to chase that fault is use an old fashion timing light. You can use it to check which cylinder is not firing. As stated above - I bet you are on one cylinder. I had a similar situation on a V4 that dropped one cylinder and I could not achieve max rpm under load....... that turned out to be a simple coil issue.
 

909

Chief Petty Officer
Joined
Jul 19, 2021
Messages
537
Pull a plug wire while it's running . If it dies, that's the only cylinder running.
 

stone71

Cadet
Joined
May 16, 2023
Messages
6
OK found out coil pack was bad on one cylinder, change it out with another one I had on one of my other Johnson motors. Now problem is it won't turn off with key cause of that coil pack. What did I do wrong?
 

stone71

Cadet
Joined
May 16, 2023
Messages
6
OK found out coil pack was bad on one cylinder, change it out with another one I had on one of my other Johnson motors. Now problem is it won't turn off with key cause of that coil pack. What did I do wrong
 

stone71

Cadet
Joined
May 16, 2023
Messages
6
The grounds connected good never connected any other wires except for the ground and the positive yellow wire and now it days running with ignition off once it started
 
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