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1992 90 HP 3 cylinder two stroke

R

Rob Merc

New member
I am new to this forum.Want to start by saying hi to everyone.I just acquired a 1992 mercury 90 hp two stroke.And Im kinda lost with this.Motor runs good,But rich which is better then lean.I rebuilt the carbs and fuel pump last week just to make sure I knew that the boat was getting the correct fuel,So I didn't end up with a new old burnt up motor.Not knowing any history on this.Now I having a starting point.On the top of the crank casing it has a nipple with a little hose that runs down to a nipple on the bottom of the crank casing.The hose keeps blowing of the bottom nipple,while the hose was off I notice there was fuel spitting out of it.So I replaced it with another clear hose.Is there suppose to be gas coming from there.If I run it with the hose connected it smokes and runs a little rougher.after running it with the hose hook up.And shut the motor off,disconnect the hose, fuel leaks out for a couple seconds.Then when I start it back up it smokes less and runs smoother.I think the nipples are something to do with crank pressure but I'm not sure.If so why would there be fuel getting into the crank case, is this a sign of something wrong,maybe a head gasket.I have no clue.Any information would be appreciated.
 
Re: 90 HP 3 cylinder two stroke

they feed the upper and lower bearings with oil/fuel, each fitting has a check valve built into it. I would check the fitting to make sure it allows oil/gas in, but not out. Then due a compression test to make sure there is something there and not all blowby blowing the hoses off....jb
 
Re: 90 HP 3 cylinder two stroke

Thank you very much for the reply..I did a compression test and all three cylinders are 120-123 compression good .I had no clue about crank bears being feed fuel-oil.Guess thats good there is fuel running though thereThank god. Though that there was something wrong.Thats a very smart set up.Seems like the top fitting sucks and the bottom blows is that correct I can;t find any info in my manual for this.I'm very curios How and were is fuel feed to the crank bears.
 
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Re: 90 HP 3 cylinder two stroke

Those little tubes (scavenge) "extra" oil/gas mix from the reed valves (behind the carbs) to keep the upper and lower main crank bearings lubed (as John noted). You won't find alot of info on them, even in the factory service manuals other than the routing for the hoses and how to check the "check" valves.

You can use a syringe with a little tube in place of the needle part. Suck up some alcohol (automotive gas line anti-freeze is safe and cheap). You should be able to get it to go (into) the fitting, but if you try and draw back nothing should happen. If you get some air bubbles in the syringe, the valve is shot.

A shot valve can lead to bearing damage.

(gas line anti-freeze can also be used to clean carb jets, so it's ok to get it "into" the engine - it's only slightly (chemically) different from the "ethanol" that's in E-10 fuel commonly sold at gas pumps now)
 
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