What is the exhaust tube fitting? Is that an exhaust tube for the exhaust pressure relief that is on the back of the motor, just under the cowling that tends to fill the laxarette with exhaust fumes? If it is, could you describe it for me?
What is the exhaust tube fitting? Is that an exhaust tube for the exhaust pressure relief that is on the back of the motor, just under the cowling that tends to fill the laxarette with exhaust fumes? If it is, could you describe it for me?
Exactamundo, Cap. Been in use for several years and works fine. I just found a piece of soft copper tubing whose OD almost matched the ID of the relief port. I think it was 5/16 air conditioner tubing. I carefully tapped it into place with a small plastic mallet and then curved the outside portion up to about the parting line of the housing. From there I use a length of fuel line to a small barbed bronze through-hull in the transom. I use no clamps and just slip the fuel line off the tubing when I raise the motor. Zero fumes in the lazarette and it looks cool too, puffing thru the transom port. The motor is wintering in my shed-I'll post a photo soon.
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Outboard exhaust has been the bane of Ariel/Commander sailors since year one. The first edition of the Association's manual had the following: "Outboard motors operating in the confines of the lazarette will frequently choke on their own exhaust gases. One solution for Johnson/Evenrude motors is to attach a length of neoprene hose over the upper exhaust port and tape in place. " Later, a member submitted a better fix using a hose nipple threaded into the exhaust port. Our current Mercury ob has two small exhaust ports in a rectangular protrudance in about the same location. Still trying to figure out a fix for it.
My Nissan 4-stroke seems to shoot it all clear of the stern through the prop . I haven't noticed any fumes at all like the Johnson/Evinrude 2-stroke made .
That's one of the 4-stroke's real advantages - underwater exhaust.
Mike,
I've been thinking about solving the exhaust problem with a 96 Merc 9.8, and after reading this stuff, its clear, if you have the money, go for a four stroke. Bye Bye Merc.
Kent
Theis, here is the photo of my outboard exhaust tube as promised. Hope the size comes out ok...
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Once again....Evinrude exhaust tube-
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My Nissan 5 hp 2 stroke also shoots the exhaust out through the prop.
But, maybe not all of it. If the Nissan, Yamaha, and Merc are all the same engine, then you do have an exhaust relief vent somewhere above the water. The Merc's is on the aft side of the upper shaft about 10 inches from the head.
It's Nissan ,Merc and Tohatsu , all built by Tohatsu .
Here's the upper exhaust port on the Mercury et al.
That photo is of a 5 hp 2-cycle. The 4-cylce engines I looked at today all have the same exhaust port.
To eliminate the exhaust gases in the lazarette, I'm thinking a cover with a hose could be placed over the ports to direct the exhaust gases under water. Or, maybe a couple of hose nipples could be tapped into the holes . . but maybe the housing is too thin. Dan's idea of a hose glued into the hole may be the way to go . . .
Bill,
For this engine, you could solder up a copper manifold, using two tight fitting tubes fitted to the motor leg ports, soldered to a horizontal plenum (1/4" tubing) which could be connected to a hose leading to some type of thru-hull fitting. To route the exhaust down the motorleg into the water just lets it boil up back into the lazarette to choke the motor at idle and low speed.
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I thank you all. This pretty much answers my concern about where the exhaust was coming from - the alternative being that it was being sucked up from the prop, or from a hole/gasket in the lower unit. My Yamaha has somewhat irregularly shaped square holes. I tapped them for two 1/4" aluminum tubes (I was concerned about corrosion using a dissimilar metal) and they are held in with some compound surrounding the outside.
The reason there is an exhaust problem, from what I have gleaned from Yamaha and various marinas, is that the prop exhaust is some distance, let us say one foot, under the water and that builds a back pressure. At high speed the prop supposedly sucks all the exhaust out (I don't believe that). However, at lower speeds the back pressure from the one foot deep prop prevents the exhaust from escaping through the prop and it must escape through those little holes. If those holes are blocked, the engine gets gunked up, the spark plugs foul, and the motor dies totally unexpectedly after several hours of flawless operation.
So now that I know this is a common problem, I am going to make sure that those holes are ported outside. Thanks for the help.
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