1976 70 hp out board probs

[tphawk09]

hi new to all this but i purchased a boat with this motor and ran great for 2 days ,then yesterday as we were coming in i noticed the motor star to lose power ,i got it to dock.my problem is it idles great ,revs up. but as soon as i put it into gear and throttle it dies. i change plugs ,carbs look good and clean but notice that the middle cylinder spark plug still looks new ,as the others show some light brown burn ,seems to have a good spark ,but looks like water in there when i pull that plug ,blown piston? any help would be great

 

[mrcj001]

Re: 1976 70 hp out board probs

Check the compression on all cylinders,the readings should all be pretty close the same.

Do that and report your findings and we`ll go from there.

 

[tphawk09]

Re: 1976 70 hp out board probs

hi thanks for replying ,its 110,54 104 ???? what do u think?

 

[Al-53]

Re: 1976 70 hp out board probs

next step is to pull the head....check head gasket....you may have blown it....if it shows its gone..replace it...then redo your compression check to see if it came up....clean the mating surfaces on head and block good....also check head for flatness on a piece of glass to make sure its flat and not warped....

Al

 

[jtexas]

Re: 1976 70 hp out board probs

yup, hopefully not more than a head gasket.

that gasket blew for a reason...you may never find out why, but don't put the motor back in service without rebuilding the carbs and water pump, test the thermostat and replace the poppet valve springs. And test the overtemp warning horn.

 

[tphawk09]

Re: 1976 70 hp out board probs

over temp horn???????? what do u mean is there a horn that beeps when its overheating???

 

[Daviet]

Re: 1976 70 hp out board probs

Look at the top of the cylinder head next to the thermostat for a single brown wire, that is the temp sender. Slide the rubber protective boot back where the wire is connected, with the key ON ground the brown wire connection to the block, the horn should sound. That is what it will sound like when it overheats.

 

[tphawk09]

Re: 1976 70 hp out board probs

thanks all headgasket was the problem cheers