reed valves

[piston eater]

I WAS WOUNDERING HOW RESTRICTIVE ARE REED VALVES IN A 2 STROKE
I KNOW THEY NEED THEM BUT IT SEEMS LIKE THEY ARE HOLDING THEM BACK. WHY DONT WE HAVE A MECHANICAL VALVE THAT OPENS AND CLOSES
WITH THE CRANKSHAFT

 

[Rcannon]

I wont attempt to answer this on a technical side, but years ago many of the bikes did not have any sort of reed assembly.

Have you ever seen a post saying "I want to have power just like my 1972 KX 250 had!" There is a good reason.

 

[RM_guy]

As Rcannon said they never used to have reeds. They used piston port induction to open and close the intake port. The length of the skirt on the intake side determine when the port opened and closed. You could cut the skirt to tune the power but I wasted a lot of pistons doing that. The only path for fuel/air to flow from the carb was through one intake port. It really limited how much fuel you could get into the combustion chamber.

Later the rotary valve was introduced. It was basic a mechanical reed valve but it took up a lot of room and weight and was located on the side of the engine case. It let more fuel in but lighter reeds won out in the end.

 

[Rcannon]

RM guy, I was too young at the time to remember much in the way of technical things, but I remember those bikes loading up constantly unless the bike was run very hard.. Was this part of the problem?

 

[RM_guy]

I don't recall them loading up bad. If they did it was due to some jetting problem.

I remember buying a new '75 TS 125 with my paper route money and stripping off all the lights so it looked cool. I then dove into the motor to see how much more power I could get out of it. I was 15 at the time and really had no idea what I was doing. As soon as I heard about the latest gimmick to coax power out, I tried it. That little bike was very abused in due to my tinkering. The big buzz word at the time was to "change the jetting". OK, cool, so I changed the jetting...and promptly seized the thing. From that point on (for a few years at least) I didn't mess with the jetting. I guess my point is that through all of my tinkering, I never had problems with it loading up so the jetting must have been pretty good to start with.

Sorry for rambling ;)

 

[piston eater]

IF I HAD SOME IDEAS OF A MECHANICAL REED WHO WOULD A PERSON GO
TO WHTH THEM

 

[David Trustrum]

Go see Eyvind Boyesen he knows about this sort of thing, tell him I sent you. If he acts all confused & like he’s never heard of me it’s just a rouse because he never returned my Boney.M album.

PS if he thinks your idea is good watch he doesn’t patent it & claim it for himself, I remember back in the early 70s in the pub we were talking & I mentioned this idea about insects having double wings. He went all silent & I haven’t heard from him since.
:|

 

[piston eater]

thanks