cowl air inlet on mercury 9.9.

[cyclops222]

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]

So....the motor runs fine without the cowl on ?

oddly, yes it does.

 

[airshot]

oddly, yes it does.

Wow....that is weird !

 

[billhig]

So....the motor runs fine without the cowl on ?

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

 

[airshot]

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]

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]

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]

Sure looks like a factory screwup.
Oh well

 

[billhig]

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]

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]

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.

 

[cyclops222]

A winner. Good trouble shooting.

 

[billhig]

Well, it's better but still distinctly different when the cowl is on. The video with the cowl on is edited to repeat because the instant you start recording it stops doing its trick for a few seconds. The repetition rate in the editing video is about what it actually did most of the time. I'm thinking I'm going to live with it. There is still a fair amount of visible exhaust around the transom and motor. Don't know if that's normal.

 

[racerone]

Might just be a sparkplug wire shorting to the cowling.

 

[billhig]

Might just be a sparkplug wire shorting to the cowling.

I've already planned to replace the plug wires but I doubt they are the issue. they are not touching and the cowl is non-conducting.

 

[tphoyt]

It can and does happen

 

[billhig]

It can and does happen

I have changed the plug wires but I don't know when I'll get out again to test it.