• Welcome to the Two Wheeled Texans community! Feel free to hang out and lurk as long as you like. However, we would like to encourage you to register so that you can join the community and use the numerous features on the site. After registering, don't forget to post up an introduction!

2 stroke reed valve

Joined
Mar 11, 2014
Messages
623
Reaction score
76
Location
@ustin, TX
Found out yesterday that one of the flaps on the reed valve for my KTM300 was broken, and I've got some questions:

1) Why is the reed valve so delicate? 4 stroke motors have valves to direct airflow and maintain pressure on the upstroke of the piston too. It's metal, if I remember correctly.

2) What are the symptoms of a malfunctioning reed valve when the motor is running?

Thanks.
 
Found out yesterday that one of the flaps on the reed valve for my KTM300 was broken, and I've got some questions:

1) Why is the reed valve so delicate? 4 stroke motors have valves to direct airflow and maintain pressure on the upstroke of the piston too. It's metal, if I remember correctly.

2) What are the symptoms of a malfunctioning reed valve when the motor is running?

Thanks.

Two stroke reeds are not delicate at all. They take a major amount of abuse since they open and close with every stroke of your engine. Think about an average two stroke RPM say around 5K and you get the picture.

Simply put, a reed valve on a two stroke opens on the upstroke to let fuel/air into the cylinder and closes and seals on the down stroke when the fuel mixture ignites.

Two stroke reeds are a maintenance item, that most forget about until their engine sucks a reed and does not run correctly. Symptoms are overall poor engine performance, hard starting, etc. Basically it will run but it depends on how much the reed cage is sealing in its damaged state.

Aftermarket reed manufacturers are ubiquitous and market all types of benefits. Reeds also help atomize the fuel ,and aftermarket reeds have some claim around making that process better. Also, material is often carbon fiber on aftermarket reeds, although OEM manufacturers also use carbon fiber stock nowadays.

Biggest issues for the DIY who is dangerous with a screwdriver in his hands is not installing the cage screws that hold the reed valves in correctly. The screw lets go, bounces around your combustion chamber and cylinder, and carnage ensues. Word to the wise.

Four stroke engines and their valve trains are so different they are really not analogous at all to a two stroke other then the opening and closing during the combustion process.
 
...a reed valve on a two stroke opens on the upstroke to let fuel/air into the cylinder and closes and seals on the down stroke when the fuel mixture ignites.

Two stroke reeds are a maintenance item, that most forget about until their engine sucks a reed and does not run correctly. Symptoms are overall poor engine performance, hard starting, etc. Basically it will run but it depends on how much the reed cage is sealing in its damaged state.

When I was looking through where the reed valve sat and saw the crankshaft it did confuse me a little bit...but I was more interested in getting a new reed valve and gasket than that at the time. Your correcting my understanding of the cylinder direction in the reed valve operation tipped the next domino for me to get my internet surfboard out.

Nice wave. Now I understand better why it can hold up as a plastic/CF part.

That also could explain in part why I'm seeing a problem I'm having with my trials bike...which has a different problem but still helps me.

************

And appreciate your highlighting the need to attend to any cage screws properly. The 300 came with a Vforce3 reed, which doesn't have screws inside to hold the reeds in place...but haven't looked at my trials bike yet...
 
Last edited:
Two stroke reeds are not delicate at all. They take a major amount of abuse since they open and close with every stroke of your engine. Think about an average two stroke RPM say around 5K and you get the picture.

Simply put, a reed valve on a two stroke opens on the upstroke to let fuel/air into the cylinder and closes and seals on the down stroke when the fuel mixture ignites.

Two stroke reeds are a maintenance item, that most forget about until their engine sucks a reed and does not run correctly. Symptoms are overall poor engine performance, hard starting, etc. Basically it will run but it depends on how much the reed cage is sealing in its damaged state.

Aftermarket reed manufacturers are ubiquitous and market all types of benefits. Reeds also help atomize the fuel ,and aftermarket reeds have some claim around making that process better. Also, material is often carbon fiber on aftermarket reeds, although OEM manufacturers also use carbon fiber stock nowadays.

Biggest issues for the DIY who is dangerous with a screwdriver in his hands is not installing the cage screws that hold the reed valves in correctly. The screw lets go, bounces around your combustion chamber and cylinder, and carnage ensues. Word to the wise.

Four stroke engines and their valve trains are so different they are really not analogous at all to a two stroke other then the opening and closing during the combustion process.

Yes, thanks for the word on the screws... A slight dab of blue Loctite goes a long way. :rider: I replaced the ones on Shauna's 125 not long ago. I don't think they were really bad, but I see light in the cage. It was just really on the low side of compression that was causing the issues. Kind of a little bit of everything. Fat jetting and a log compression make for a poor running bike. A new piston and she has go again!
 
Back
Top