could anyone explain to me how reed valves works?

Question

I have a 86 75hp merc. outboard and my bottom carb doesn't constantly pump gas and I was wandering if my reed valves could be a factor.

Answer 1

Reed valves work like the reeds of a wind instrument. Two tightly fitting pieces of thin metal are attached to a wedge shaped frame so that air can be forced through them.

On a two stroke engine, the spark ignites the fuel at the top of the piston's upstroke, pushing the piston down. The descending piston pushes the fuel-oil-air mix out of the crankcase through the reed valve on the inlet side of the cylinder, which in turn pushes the exhaust gasses out the exhaust port. Inertia carries the piston through the bottom of the center, and the crank and fly wheel push it up, closing the exhaust port, and compressing the mix that was just pushed into the cylinder before burning it and repeating the cycle.

More than likely, if you've got reed valve problems, you've got a power problem, really smokey exhaust, a notable miss and a spark plug that continually needs cleaning. Otherwise, chances are, your pump is just filling the float bowl and waiting until the float opens the valve and allows more two stroke mix into the float bowl.

Or you could have a faulty pump. Don't know if its electrical or mechanical, but this should be a troubleshooting start.

JT

Answer 2

Reed Valve

Answer 3

A reed valve is a one way valve that allows flow in one direction only. Reed valves have nothing to do with the exhaust. A two stroke engine's intake system is under a vacuum like a 4 stroke engine at times but the two stroke also has a time where there is positive pressure in the intake system. The reed valve allows air from the carburetor to enter the intake system when vacuum is present but closes and wont let air escape back thru the carburetor during high pressure.

Leaking reed valves will cause high pressure to blow back toward the carburetor causing less fuel flow.

Answer 4

Wiki is good for a picture;
http://en.wikipedia.org/wiki/Reed_valve
They cover the hole from the carb and open only in one direction as the piston pull vacuum.
I not think this would be your problem, though they can stick.
On the Mercury there a Brass plug on the side of the carb. Your right facing engine from the front. It kinda down toward the bottom. Remove it with a 3/8 socket I think that the size. Inside is a Brass High Speed Jet. Use the proper size screwdriver to remove, be very careful not to damage this. Sometimes it is clogged and just need cleaned AND!!!! It usually happens to the bottom carb. You may try spraying with some carb cleaner before removing and see if it clear. But, you really can not see if it clogged unless it is removed.

Answer 5

These valves are thin spring steel discs, or rectangular leaves. They are subject to sticking, breaking, or staying slightly open due to foreign matter getting under them. A higher pressure on the upstream side of the valve, or a vacuum causes the valve to pull away from it's seat just enough to let the controlled fluid, or gas through. Clean the affected area, and if that doesn't work, they'll need to be replaced.

Answer 6

A reed valve works by being sucked down or pushed up by the motion of the piston. The intake valve only moves down, and the exhaust only moves up sort of like a trap door.

Its a neat system of valve operation I used to repair in the Navy on the air compressors.

Answer 7

When the piston goes up it creates a vacuum in the crankcase. The carbuerator feeds directly into the crankcase through a one-way valve (reed valve). Obviously the piston going up also accomplishes the ignition stroke and BANG. When the piston goes down it creates pressure in the crankcase. The gasses in the crankcase flow up into the combustion chamber through vents machined into the cylinder wall which are exposed when the piston is in it's low position. The gasses going up from the crankcase displace the exhaust gasses remaining from the previous ignition cycle. It's not a perfect expulsion of exhaust, but hey, it's good enough to fill the cylinder with enough fuel-air mixture to ignite & create another BANG. And the process repeats: BANG-squish-whoosh-suck-BANG-squish-whoo... etc. etc. etc.