What's the pupose of reed valves?

[yamy]

What's the purpose of the reed valve assembly? Does it act like a choke? The reason I ask is because I have a 1982 (J1700 series) Yamy and I think the previous owner removed it. I see in this diagram (scoll down to air filter page)

http://www.mtsassociates.com/yamaha/1982/G1_A3.pdf

that it appears to fit between the input side of the carb and the air filter can. Do I have that right?

Anyway, I don't seem to have one of these things and was wondering if I should. It seems to run fine without it, although I do have to give it lots of choke to start it when it's cold.

[smallblock450sl]

Originally Posted by yamy

What's the purpose of the reed valve assembly? Does it act like a choke? The reason I ask is because I have a 1982 (J1700 series) Yamy and I think the previous owner removed it. I see in this diagram (scoll down to air filter page)

http://www.mtsassociates.com/yamaha/1982/G1_A3.pdf

that it appears to fit between the input side of the carb and the air filter can. Do I have that right?

Anyway, I don't seem to have one of these things and was wondering if I should. It seems to run fine without it, although I do have to give it lots of choke to start it when it's cold.

The reed assy fits into the cylinder, behind the rubber manifold that the carb slides into. Don't see how it would run without them. Basicly, there a one way check valve, as the piston creates a vacume (intake stroke) the reeds open enough to alow the gas/oil mixture to be sucked from the carb. They must be closed to alow for the compression stroke. Or something like that. Most times haveing to choke is a sign of bad crank seals (as long as you have good compression and the carb is clean and the throttle shaft is not worn out causing an air leak).

[Pocono Country Boy]

A reed valve assembly would not be between the carb and air cleaner...it would be on the other side of the carb.

Needing to choke a lot to start it only could also just mean you need to replace your fuel filter(s) and/or your fuel lines...or maybe just tighten or replace any clamps..or possibly your fuel pump is weak.

I always try the easiest/cheapest first...then if you need to go further you at least know that it's none of those things and you are not out loads of cash, time and aggravation to find out.

In my case, I found that the lines were deteriorated and filters pretty much plugged and the carb was in real need of a good cleaning. Once I did those things everything was just fine. I still need to choke it for the first start of the day or if it's been sitting for more than 3 or 4 hours but as soon as it fires up it runs fine without it.

[technoid]

Originally Posted by yamy

What's the purpose of the reed valve assembly? Does it act like a choke? The reason I ask is because I have a 1982 (J1700 series) Yamy and I think the previous owner removed it. I see in this diagram (scoll down to air filter page)

http://www.mtsassociates.com/yamaha/1982/G1_A3.pdf

that it appears to fit between the input side of the carb and the air filter can. Do I have that right?

Anyway, I don't seem to have one of these things and was wondering if I should. It seems to run fine without it, although I do have to give it lots of choke to start it when it's cold.

What you need to do is read up on the basic operation of a 2 cycle internal combustion engine. There are two basic types. Reed valve operation. And porting. (Also a rotary valve type was used in the 1960's Bridgestone motorcycle engines). The purpose of the Reed valve was to close off the fuel mixture from escaping back out the carb during compression. In porting, small ports are cut into the cylinder walls at precise locations to create the right amount of vacuume for fuel intake, close off compression and allow exhaust escape during piston movement. If it had a reed valve and it was removed, your engine would not run. So it sounds like it uses the porting method.

[yamy]

Thanks guys. I thought all 2-cycle engines used the configuration of the ports to control the intake and exhaust. Now I know of another type.

I mis-read the part explosion diagram. I see now that the reed assembly is on the engine side of the carb.

Also, I found out today that I have weak fuel pump, so that's probably why I have to choke it so much. I ordered a new fuel pump, and I'll check the throttle shaft play too.

Thanks.