2000, 90 hp making "Air leaking sound"

[Rider99XX]

I have a 2000, 90 ELPTO serial# OT120836. It runs great. I fished a tournament this past Saturday and it ran great all day. After the weigh in my wife wanted to go back out for a couple hours. We stopped at a spot but couldn't get in to it due to the water levels being too low. So we rode around and looked for about an hour and headed back to the ramp. When we entered the no wake zone we could hear what sounds like an air leak. Motor had plenty of power, starts right up, runs fine. I pulled the cowl off but couldn't see anything obvious. The "air leak" sound started on our return ride to the ramp. The oil tank has plenty of oil in it, 3/4s full.

What could the "air leak" sound be?

Thanks.

[JOE54]

remove flywheel cover make sure timming pointer didnt come loose rubbing flywheel

[Rider99XX]

I will check that this afternoon. The sound is constant so that could be a possibility.

Thanks!

[Rider99XX]

Also, regardless of prop pitch, what is THE MAXIMUM rpms at WOT for this motor? It will turn almost 5500 now.

[rtlgator]

That's max....

[boatwrench]

Timing pointer on that engine is part of flywheel cover it can't get loose as is molded into the timing window on cover. Look for broken recirculation system hoses on intake manifold behind carburetors . The hoses are small 1/8 " I'D.
If you run the engine on the trailer ,use a large tub or barrel full of water instead of flush muffs , it will muffle t the exhaust and make it easier to hear "air leak" sound.

[Rider99XX]

Yep, I found out the timing pointer is made into the flywheel cover. Could the starter drive get stuck in the up position after starting the engine and cause that sound? The reason I ask is I noticed the shaft that the drive slides on is dry looking. Looks like old lube that has dried out. I didn't get a chance to start it with the cowl off. I'll start it this evening in a tub and check the hoses and the starter drive.

Thanks for the reply's!!

[grybrd]

If the shaft on the Bendix drive is dry and sticking you will be able to see the starter pinion gear remain up against the flywheel teeth after the motor starts. The lube used on the Bendix will usually look dry but still be doing its job. A wet lube would gather dirt.

[JOE54]

yes would be very noisey

[Rider99XX]

The starter shaft is dry. What's on there feels like old dried up lube of some kind. Doesn't feel like a graphite type of lube. I started the motor twice but the drive disengaged the flywheel both times and did not hear any strange noises. Just air going to the carbs. When I first heard the noise it was after about a 4 or 5 mile run at WOT. We fished for just a few minutes (10-15) then cranked back up and returned to the ramp so the motor was at operating temps when we first heard the noise. Yesterday the motor was cold. Not sure if the motor temps have anything to do with it but I'll find out this weekend.

[EuropeanAM]

Any recent PROP changes?

[Rider99XX]

No Sir. No prop change. I started the motor at home to see if the starter was stuck, it was not. I didn't see and hoses or tubes than may have come off. I did NOT hear the same sound we heard before. All I could hear was the air going in the intake as normal.

[nwest10]

I had a 2010 90HP that started hissing out of the blue. Found out that one of the gaskets between one of the carbs and the intake had deteriorated and it was sucking air. Only heard it when running above idle under load. Mechanic said the ethanol gas caused it, but I'm suspect of that.. I went ahead and had all three carbs rebuilt and all gaskets and fuel lines replaced. $600 bucks later it ran like it did new. I only found it because it backfired once when I had the cowl off and it sprayed out a mist of fuel between the carb and the intake. Did not seem to really affect the motor running, but was a really loud hiss when running. Hope you find the problem!

[Rider99XX]

I thought about the carb gaskets too. Even with my ear as close to the carbs as I could safely get I couldn't hear anything other than the normal sound of air going through the carbs. The sound mine was making was more noticeable during idle but could have been doing at other rpms.

I hope it's not the carb gaskets as that would cause a lean condition and 2 strokes do not like to run lean.

[slow530]

Try taking a 3 foot section of 3/8" tubing, holding one end to your ear then hunt around the intake listening for a leak. Should be able to pinpoint it with that.

[Rider99XX]

Took the boat out yesterday. Ran fine all day with no hissing sound. Then on the return trip we stopped to fish this one area. When I came off plane and down to an idle I could hear the "hissing/air leaking" sound. I shut it off and we fished for about 45 minutes and decided to go to another spot. The sound was gone. NO hissing sound the rest of the day. It seems to do it after a run at or near WOT.

Baffled.

[leonreno]

Maybe excess pressure from oil tank or oil system.

[EuropeanAM]

When was your water pump last replaced?

Could be STEAM from coolant in the engine that's too hot... they'll hiss like a pressure cooker when that happens.

[Rider99XX]

I didn't think about steam. Water pump was replaced last fall but the boat wasn't run until early this year. A complete pump assembly was installed, impeller, plate, and housing. Water stream is VERY strong, even at idle. With that much water coming from the engine could it still run hot? I check the stream while running to insure that it is pumping water. Could it be a thermostat??

[EuropeanAM]

That is a possibility... however, you "should" receive an overheat warning horn if it is indeed that hot (provided the warning horn is functioning).

Frustrating when trying to diagnose "sounds" by keyboard and monitor (essentially blind and deaf).