84 Yamaha 70 HP - Need Help

[yrmamaha]

Let the boat sit too long - cleaned the carbs, fresh gas, new fuel line. started good in the barrel, took it to the river - ran good for 10 mins. then died. crankin & crankin with no luck. did a compression check - top cylinder 120, middle cylinder 28, bottom cylinder 120. put oil in middle cylinder no change - still 28. Any suggestions???

 

[GoogieMan]

Re: 84 Yamaha 70 HP - Need Help

be looking at a rebuild i think pull head off and and inspect pistons could be a number of things, hole in piston, broken ring busted head gasket etc

 

[yrmamaha]

Re: 84 Yamaha 70 HP - Need Help

Googieman, good lookin out! I got it started today, took carbs off & cleaned again. Took reeds out & made sure they were gapped right, put it back together & motor fired up 4 bout 1/2 hour with ears on in gear, low idol. Could I get through the rest of the season without hammering it & re-build in the winter? Big Stripers out there!

 

[99yam40]

Re: 84 Yamaha 70 HP - Need Help

only if you want to replace the motor and maybe get stranded on the water.
If you do not have compression on one cylinder do not run it, fix it

 

[Kyle4512]

Re: 84 Yamaha 70 HP - Need Help

I just had the same problem with my 89 70hp yamaha. Middle cylinder was 25 psi and the rest 115 and 120. Took the head off and found that the bad cylinder was scored. Ended up taking the powerhead off, bought an oversized piston and rings and had a machine shop bore it out for me. Cost me about $300 between the piston, rings, bore job and head gasket, but its well worth the peace of mind that I have a healthy engine. You deffinately don't wanna run it like it is. As stated above you may end up ruining the engine. Take the head off and take a look. May be something as simple as a head gasket. Good luck!