2000, 90 hp making "Air leaking sound"

[Rider99XX]

I understand fully about the diagnosing via the internet and I applaud your efforts!!

I haven't heard any alarms and not sure if they are working. If it were steam in the coolant, would it still make the noise shortly after the engine is shut off until the temps drop? On mine the noise disappears immediately on shutdown.

The other day while I had the cowl off looking for anything obvious I noticed on the right side of the motor, at the back lower side, there is a light brown or tan wire that is not connected to anything and a black with white stripe wire that is not connected to anything. Not sure they were ever connected.

[EuropeanAM]

Not part of the problem- they are often not connected.

Have you tried running without the cowling to see if you can replicate the problem?

Any sagging foam/sound-dampening material (or plastic bag with pull start rope) inside the cowling?

[Rider99XX]

I have not run with the cowl off but will next time out. The sound dampening material is all where it's supposed to be, stuck on the cowling along with the pull rope and bag. Nothing is loose/hanging.

[straffordengineer]

My 125 Hp 2+2 started doing intermittent hissing. Ended up being a bad reed valve. Found out when the reed valve finally broke.

[Rider99XX]

A friend of mine said it could be a reed valve. I hope not.

[EuropeanAM]

They're not too bad to replace... the concern would be a broken one going through the engine.

[Rider99XX]

I know some of the symptoms of a reed going bad is spitting back through the carb in front of the bad reed valve. I know that's not the only symptom. So far mine doesn't spit back through the carbs and doesn't backfire at all.

[EuropeanAM]

That is true... although it is not an "absolute" theory (at least not the "spitting back" or lean-sneezing symptom).

There are scenarios where the only real symptoms would be "down on power" and possibly fuel failing to be drawn INTO the engine from that cylinder (and when fuel is not drawn through, OIL is not being delivered, either). This would also be a concern with any air leak in the air-intake side of the engine.

[Rider99XX]

I checked for fuel around the carbs, even with the motor tilted up and there is none. I ran it this past Sunday and it ran fine with no abnormal noise at all. Not down on power. Should I be mixing oil with my fuel just for a little insurance? If so, at what ratio of oil to gas? AND what is the BEST oil for me to run in my engine???

Thanks again Don for all your help!!

[EuropeanAM]

Mercury or Quicksilver Premium PLUS.

You could use a VERY small amount of additional oil in your fuel (some of us that have built engines for years do this with our own). NO MORE than 150:1 in the fuel (on top of functional oil injection). That's approximately 4oz per 5 gallons of fuel (max).

TOO MUCH oil is NOT a good thing- the fuel becomes thicker, and does not flow across/through the jets at an appropriate rate.

This can cause a lean running condition (resulting in the very damage you were trying to avoid).

[Rider99XX]

Great information Don. The oil injection seems to be working fine but any added protection is a good thing. The fuel tank in my boat needs to be filled up for a Saturday tournament so that will be a good time to add the oil in with the gas. Might add in the "cocktail" too.

Thanks Don!!

[dgrabs]

Hey guys, i have a 2005 mercury 90hp 2 stroke on my nitro, and i am getting this exact same issue.

No performance loss at all. Hiss air leak sound at idle. Comes and goes throughout the day.

Were you ever able to pinpoint this and get it fixed? I'm okay with the sound, i just dont want it to escalate into a bigger issue.

Thanks!

[EuropeanAM]

Hey guys, i have a 2005 mercury 90hp 2 stroke on my nitro, and i am getting this exact same issue.

No performance loss at all. Hiss air leak sound at idle. Comes and goes throughout the day.

Were you ever able to pinpoint this and get it fixed? I'm okay with the sound, i just dont want it to escalate into a bigger issue.

Thanks!

While you may feel that your engine or symptoms are very similar, it is important that each engine be in it's OWN SEPARATE post so as to avoid confusion and/or Post HiJacking.

Thanks!