Evinrude carb gasket with wire mesh opening

[frankr]

delete

[crosbyman]

a virus maybe…

ho well I just leaned not to eye ball my "new" TN27 when adjusting the L key

nothing like fresh gas to wash away coatings on new pair of glasses 😯

Joining AOMCI has priviledges 🙂

[The Boat House]

quote chas56x:

There is no chance of “residual combustion fire” left in the combustion chamber when the piston reaches bottom dead center and the exhaust ports and the intake ports are uncovered. If you look at the position of the intake ports in relation to the exhaust ports, the exhaust ports are higher up in the cylinder bore than the intake ports. The shape of the piston with the deflector on top forces the burnt fuel/air mixture to exit the combustion chamber before the intake ports are uncovered by the piston. By design, when the intake ports are uncovered, pressure in the crankcase forces the intake charge (fuel/air mixture) into the combustion chamber and the deflector on the top of the piston forces the fuel/air mixture up into the top of the chamber and actually forces any left over exhaust gasses out of the exhaust ports. The carburetor in the older Evinrudes are of the poppet type. The poppet valve in the carb moves up and down in relation the pressure/vacuum pulses in the crankcase developed by the up and down movement of the piston. During the downward movement of the piston, pressure builds up in the crankcase forcing the poppet valve in the carb to close with the assistance of a small spring on top of the poppet valve, thus forcing the fuel/air mixture up into the intake side of the cylinder. During the up stroke of the piston, a vacuum is created in the crankcase, unseating the poppet valve allowing a fresh charge of fuel/air mixture into the crankcase.
With the incorporation of reed valves, this negated the need for poppet valve carburetors. If you get any spitting back of fuel/air mixture out of the carburetor in a two cycle engine, it is caused by either a stuck poppet valve or a broken reed.

lean Sneeze
https://www.youtube.com/watch?v=jqLqzjO … e=youtu.be

The leaner the mixture the higher the cylinder
temperature becomes to the point the fuel
mixture will ignite as it enters the cylinder
before the piston has moved up enough to
close the port.

[frankr]

Yep, has a rotary valve—no reeds or poppet valve.

[george-emmanuel]

Obviously haven’t run a 6039 Speeditwin without the front cover..Oh well..

Now onto the gasket question. Most of the time the carb gasket with the mesh is there on carbs with springs on the poppet valve so if the spring breaks it doesn’t get into the crankcase and cylinders. I make my own. I have some old stock heavy bronze screen. I make two thick gaskets and coat the mating sides with some 3M gasket sealer and then press the 2 gaskets together with the screen in the middle in a flat jaw vice. I have also used 1/8th hardware cloth.

George

[david-bartlett]

quote George Emmanuel:

Obviously haven’t run a 6039 Speeditwin without the front cover..Oh well..

Now onto the gasket question. Most of the time the carb gasket with the mesh is there on carbs with springs on the poppet valve so if the spring breaks it doesn’t get into the crankcase and cylinders. I make my own. I have some old stock heavy bronze screen. I make two thick gaskets and coat the mating sides with some 3M gasket sealer and then press the 2 gaskets together with the screen in the middle in a flat jaw vice. I have also used 1/8th hardware cloth.

George

George,
I was thinking the same thing during this topic!

[Anonymous]

I’m with Frank. When I’m running my 1938 Johnson PO38, I make sure to sit sideways and keep back to the side from the vacturi with a stack because it can and has sent a fire ball a foot or more out the carb. The vacturi is a butterfly throttle plate carb.

[dan-in-tn]

Big difference between theory & experience! I will go with experience every time. Just so everybody knows two strokes were still lean spitting until DFI came along. Maybe even worse as fuel mixtures got leaner for fuel economy efforts. First outboard oil injection (1984) brought about a Flame Arrestor Kit #174624. Tied right onto the crankcase where the fuel pump hose goes to drive the fuel pump. Prevented the diaphragm on the air pump being burned from crankcase explosions (lean spits).
The first attempts were just steel wool stuffed in the braided hose to squelch the fire. Later they developed a valve (pulse limiter) that stopped the measured 75 lb. pressure spikes that would blow the air motor apart in the pump. Some serious energy in the crankcase!

Dan in TN

[garry-in-michigan]

The Elto Handitwin in question has a "check valve" carburetor. If the cork bumper is worn or damaged so the valve opens wider it will delay closing causing a decrease in efficiency and increase in tendency to backfire. A lean mix burns more slowly so at slower speeds running with retarded spark there will be fire in the combustion chamber when the transfer ports (AKA bypass ports) open which ignites the fuel mix in the crankcase. On rotary valve or third port outboards, this is the time when the intake opens so it can blow a flaim out of the carburetor. The screen is mainly to keep bugs and bits of cork bumper out of the crankcase. For those who feel it necessary, I clean off the old screen completely of any trace of gasket and put a new gasket on both sides. . . 😀

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