78 johnson 175 seems to mist water in top starboard cylinder

OQMJr

Cadet
Joined
Jul 16, 2011
Messages
10
hello, first time posting here, but been reading alot. i bought the boat a couple weeks ago, took it out a few times, it starts ok, idles ok, but tries to die when giving throttle in gear. if i play with the controls a bit i can eventually get it to speed up but it only turns about 4500 rpm. i pulled plugs and they are all wet, 5 of them look like fuel. the 6th looks like water and the piston looks steam cleaned. i have been reading the forums here and from what others have said it sounds like a head gasket to me because taking a compression test 5 of the cylinders are around 90psi +/- 2psi the one with the water is around 75. does this sound right to you and could replacing the one head gasket get the boat to rev up the rest of the way?
or should i look into doing more extensive repairs? all coils fire good and shock the crap outa me when i pull wires while engine is running. engine doesnt drop any when i pull the one off cylinder in question and the carbs were recently rebuilt. i think the guy who owned it before was scared to do much, because the coil on the cylinder in question looks brand new. but the heads look like they havnt been touched in years. im new to outboards so i hope i provided all the neccissary information
 

jayyyy

Seaman
Joined
Jul 17, 2011
Messages
52
Re: 78 johnson 175 seems to mist water in top starboard cylinder

I think your on the right path. A clean piston screams water intrusion. Hopefully there is no cylinder scoring and its just a head gasket R&R.
 

Solittle

Fleet Admiral
Joined
Apr 28, 2002
Messages
7,518
Re: 78 johnson 175 seems to mist water in top starboard cylinder

Head gaskets are cheap and will allow you to have a look see. I'd do it before you run it much as you might do some severe damage.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 78 johnson 175 seems to mist water in top starboard cylinder

Follow Solittle's advice. If you have an exhaust gasket water leak, it tends to affect the lower cyls.
 

OQMJr

Cadet
Joined
Jul 16, 2011
Messages
10
Re: 78 johnson 175 seems to mist water in top starboard cylinder

Thanks for the help guys. will order the gasket today, and a new set of plugs. I read on here somewhere that head gaskets should be replaced every few years regardless? so should i go ahead and replace both and decarb while its open to see if i can get the compression up all the way around, 90 seems a bit low even though the readings are really close together on the other 5 cylinders, or is that normal if it has low compression head gaskets? i want to get this motor right, its on a 76 v-20 so i dont want to upgrade to a newer engine unless i have to, i like old and simpler. boats not the prettiest but solid, and all i do in it is fish the lower chesapeake bay.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 78 johnson 175 seems to mist water in top starboard cylinder

The new compression with factory heads would be in the 110 range. Yours is down somewhat, but should still run fine. Head gaskets get replaced when they leak, such as the one you have. Not a normal scheduled maint. item.
 
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