cowl air inlet on mercury 9.9.

cyclops222 · Saturday at 3:27 PM

It runs better.
By chance is there any SOUND INSULATION glued to inside of the cover in front of the air inlet to the engine ? it can come loose at high airflow rates. And block some of airflow at WOT. Then swing back to cover surface as engine speed drops.

billhig · Sunday at 8:03 AM

airshot said:
So....the motor runs fine without the cowl on ?

oddly, yes it does.

airshot · Sunday at 10:02 AM

billhig said:
oddly, yes it does.

Wow....that is weird !

billhig · Tuesday at 9:28 AM

airshot said:
So....the motor runs fine without the cowl on ?

Yes, it does. That's why I'm so confused.

airshot · Tuesday at 12:30 PM

billhig said:
Yes, it does. That's why I'm so confused.

Remove that piece on the handle area on the inside and see if that helps.

billhig · Tuesday at 4:38 PM

airshot said:
Remove that piece on the handle area on the inside and see if that helps.

I tried that and it had little or no effect. it should be getting plenty or air now. I also pulled the exhaust plate and that gasket is in perfect shape. no exhaust leaks there.

airshot · Tuesday at 5:11 PM

OK....gotta ask, are you sure there are no wires being pinched ? No linkage being bound up when the cowl slips on ? This should not be so complicated ..

cyclops222 · Tuesday at 6:00 PM

Sure looks like a factory screwup.
Oh well

billhig · 2025-08-27T07:59:52-0600

airshot said:
OK....gotta ask, are you sure there are no wires being pinched ? No linkage being bound up when the cowl slips on ? This should not be so complicated ..

I know. There is nothing touching the cowl at all. I think it has to be air/exhaust related.

billhig · 2025-08-27T08:00:35-0600

cyclops222 said:
Sure looks like a factory screwup.
Oh well

it's a 25 year old motor (new to me). I can't imagine it did this its whole life.

billhig · 2025-08-28T16:03:49-0600

I think I might have got it. I noticed exhaust coming out the shift shaft hole while running it in a tub. That exhaust is shooting up directly at the opening in the cowl and choking the carb.
I read the manual again and realized I left off the RTV the second time I replaced the water pump. The sole purpose of that RTV is to keep exhaust out of the shift shaft / driveshaft/water pump space. I will test and report back.

cowl air inlet on mercury 9.9.

Commander

Cadet

Vice Admiral

Cadet

Vice Admiral

Cadet

Vice Admiral

Commander

Cadet

Cadet

Cadet

Attachments