Johnson 70hp seahorse

M

Myreng

Recruit
Joined
Jan 29, 2013
Messages
1
Hi guys, need help, my 70 up seahorse runs great until it hits the water, then it bogs down and if it doesn't,t quit altogether, she runs at pre plane. I took off the lid while running in water and revved by hand and noticed a little water bubbling in the lower center area. Is this a clue? I am a novice and could use some advice from guys with experience.thanks
 
trendsetter240

trendsetter240

Lieutenant
Joined
Jun 22, 2009
Messages
1,458
Re: Johnson 70hp seahorse

Can you take a pic of where the water is bubbling out?

My first step would be to test the compression on the motor. You're looking for 100psi+ and within 10psi on each cylinder.

Other items that come to mind are the fuel pump / fuel line primer ball are failing. This can be tested by running the motor and having someone pump the primer ball while the engine bogs to see if that helps.

Also could be one or more carbs are dirty and causing a cylinder to run lean. Start with the compression test though and go from there.
 
eavega

eavega

Lieutenant
Joined
Apr 29, 2008
Messages
1,377
Re: Johnson 70hp seahorse

As the previous poster commented, check compression, and spark. Also, do a cylinder drop test. that would be when you start the motor, then pull the plug wires one at a time making sure the other two are plugged in. If the motor has no change when you pull a spark plug wire, then that cylinder is not firing for some reason.

If that is the case and compression and spark check out, then you probably have a fuel delivery problem. since there is only one fuel line that feeds all three carbs, if you have a fuel problem on one cylinder its probably a dirty carb.

Good luck.

Rgds
 
S

shawn.54

Petty Officer 2nd Class
Joined
Jun 21, 2012
Messages
104
Re: Johnson 70hp seahorse

Had same problem with 78 75hp evinrude took plate off front of carbs bottom cylinder was not getting any fuel rebuilt carbs replaced bad lines between carbs. grabed a buddy and fishingpools went the the lake had a 75 horse 9.9 pulled plate top carb no fuel to make long day short after removing top carb 4 or 5 times on the water some smart a## had put a ball bearing in new fuel line. got that out she runs great. if you repace lines blow through them first.
 
D

durban

Master Chief Petty Officer
Joined
May 27, 2011
Messages
894
Re: Johnson 70hp seahorse

now when you say lower center area ? are you refering to the center plug on the outside of the cylinder head cover if theres water comeing out there then you have a gasket problem , the water can affect your spark as you throttle up the poppet valves will open up allowing more water presure to flow out through the cover on the out side of the cylinder head & under presure could be sqiurting onto your plug cap& cause a miss fire , best you upload a photo then we know more & then in a better position to help , cheers
 
E

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: Johnson 70hp seahorse

The engine may not be running on all 3 cyls. That engine may seem to run just fine on the trailer with only 2 cyls firing. It's a different story when the prop is buried 2 feet under water. You need all 3 cyls firing at that point. If you've got an inductive timing light, you should be able to check for spark at all 3 plugs. Best to check when the boat is floating, fully warmed up and idling in gear at the dock.
 
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