70hp mariner 1984 run great with muffs won't run in water

[ronstas]

I have a 70hp that only in the water you try to go engine dies like it has no fuel.was put on dyno several times where it performed flawlessly,the engine has carbs overhauled twice, tune up, trigger, control box,new fuel, fuel pump,filters ,lines,new prop,2 diff repair facilities can't fix,whats possabilty of the water back pressure prob

 

[emckelvy]

Re: 70hp mariner 1984 run great with muffs won't run in water

A dyno may not simulate the backpressure of sitting in the water. You can try increasing the idle speed. If there's a mixture adjustment on the carbs, you'd want to adjust the needles to richen the mixture (CCW).<br /><br />How about a compression check, has anyone done that?<br /><br />You also may have issues with the upper or lower crank seals; loss of crankcase vacuum will affect idle quality, especially in the water.<br /><br />Has anyone checked the plugs for water after one of the 'dying' incidents? If you find water on the plugs you could have leaks from the exhaust manifold or gaskets.<br /><br />There's also a remote chance that there is some restriction in the exhaust, maybe it's time to pull the lower unit for examination. Also look up the exhaust tube and check for obstructions such as carbon deposits.<br /><br />You'd think that the dyno runs would be affected too, but you never know. It is, after all, a 2-stroke marine engine!!!! lol<br /><br />HTH and Good Luck............ed

 

[ronstas]

Re: 70hp mariner 1984 run great with muffs won't run in water

thanks ed, I know the comp checked out good,I don't know if the 1st shop checked for exhaust restictions,they did have the lower off they put in a water pump,the carbs have been adjusted and adjusted,I am starting to think the seals are a good possabilty and or the carbs are junk'if you have any more info it would be appreciated and I will check the plugs at the dying time . thanks ron