This isn't stock, is it?

[DHag]

I have a 1978 Mercury V-150 V6. It's 2-stroke, of course.

It's very loud when running. On a minimum plane at a slow 20 mph, you have to shout to talk to the person sitting next to you. Wide-open, forget it. It also idles rough, and loads up and stalls when idling.

See the attached picture. I thought the six neatly-drilled holes (red arrows) in the back of the midsection were part of an "idle relief" system. But that would be the two ports marked with green arrows, correct?

Every parts picture I can find has the exhaust tube turned the other direction, so I can't see what it's supposed to look like!

I finally took a close look at the six holes. Behind those are six matching holes in the exhaust tube. I think a previous owner thought he would get more power by letting back-pressure off of the exhaust. Or maybe he just wanted it loud. But understanding 2-stroke dynamics, this could be the cause of my poor idle, and it is probably the source of the noise level.

Am I right, and these are not stock? If so, I'm going to put plugs in the exhaust tube behind these holes.

 

[zanderman111]

Re: This isn't stock, is it?

I tried to find some pictures of your engine, but couldnt find any with the right angle either. From the look of the holes in the picture, I am going to say that they are not stock. If they were stock, they probably would have had some kind of beveling like the two stock holes above. The previous owner probably just wanted an attention getter or else thought it would make it more powerful. Just from the look of it though, I would agree with you in saying that they are not stock.
Also, I have a 1979 90hp merc and it does not have those extra 6 holes. In fact I cant find any pictures of any outboards with holes like that.

 

[Faztbullet]

Re: This isn't stock, is it?

No that is not stock!!! Someone drilled them to get that Hi-po sound and think it would help hp wise. You are correct, the exhaust can is behind the outhousing. Plug emand you will be able to hear and talk plus pick up a little hole shot power. It may be the cause of some of your low end problems as exhaust gas could be comming back under the cowling.