Window piston/reed valve. Vs ported cylinder no window no reed

[throttlejockey]

Hey guys so I've been building for a long time and ride this to work and back EVERY day for years. So am very familiar with these motors. I have done a lot to my motor and bike for upgrades and get about 4 HP out of my YD100
I prted the cylinder 1mm on sides and bottom of intake 1mm on sides and top of exhaust. Stuffed the case have all upgraded electric parts. Stater magneto oz magnet NIBBI racing coil. Stand alone CDI. NIBBI racing carb 24mm. Aluminum billet clutch plate with the better clutch pads black ones. 36 tooth sprocket.
So the thing screams but I am having trouble getting more power with the window piston and reed valve. When running my sloped and scrirted stock piston with no reed I get more power and top end more all around. With a reed and windowed piston I get less bottom end and less top end just less all around. I need somebody that can possibly help with how to squeeze the proper power out of the window and reed. Please no stupid comments like is it tuned right lol. Or obvious crap please and thanks.

 

[throttlejockey]

View attachment 116354

 

[Venice Motor Bikes]

Rule #1 of installing a reed valve is to throw more gas at it!!! (try installing bigger jets).

 

[throttlejockey]

That's the first thing I said. No comments like stupid stuff like throw bigger jetts yes you have to jet up it was tuned perfect with and without reed piston set up and just still didn't have that balls as without the windowed piston. Please someone with extensive knowledge get back to me I am a very experienced mechanic I know port timings and have a 4.5 HP motor

 

[throttlejockey]

I've tried every shape and size hole in the piston I've tried many things rich lean everything and not saying it didn't run great with the windowed piston and Dio reed valve. But way way faster with a sloped and skirted stock piston with no reed. It is crazy powerful without the reed valve and with it no matter what just doesn't compare

 

[Wevil Kenevil]

I've tried every shape and size hole in the piston I've tried many things rich lean everything and not saying it didn't run great with the windowed piston and Dio reed valve. But way way faster with a sloped and skirted stock piston with no reed. It is crazy powerful without the reed valve and with it no matter what just doesn't compare

Slow down turbo!

 

[Wevil Kenevil]

That's the first thing I said. No comments like stupid stuff like throw bigger jetts yes you have to jet up it was tuned perfect with and without reed piston set up and just still didn't have that balls as without the windowed piston. Please someone with extensive knowledge get back to me I am a very experienced mechanic I know port timings and have a 4.5 HP motor

Really? When you figure it out let us know!

 

[Venice Motor Bikes]

That's the first thing I said. No comments like stupid stuff like throw bigger jetts

Maybe you should try using more JB weld & zip-ties

 

[rotax]

Hello, hope you have everthing worked out. But maybe I can help a little. I started racing Go-Karts in the mild 60's till the early 90's Twin engine, Opens & 100cc stock. Running a reed valve with a window piston you run into a wall at some point. The Reed valve is good for higher RPM's the Window Piston makes great Tork. When you hit higher rpm's the Window piston starts opening and creates a back pressure on the reeds holding them open to long or holding closed to long. In racing you can use this a tight track use the tork for pulling out of the corners then drope a couple teeth off the rare sprocket. you pick up some top end speed without over Revving. But it sounds like your looking for more top end Rev's. Go Reed valve, lose the window piston. Your new piston try to get someone to ceramic coat the top then cut about 10 thousands off the bottom of the skirts of the piston to lighting it up + your reeds open just a little sooner. Can I ask is that your Bike in the photo at the start? If it is, your losing a lot of power bye the way the carb- is mounted. The carb- should be as close to your Reeds as you can or to the intake port. You want a straight a shot as you can get into your engine. That 45degree turn is a big big air restriction. The air is running into a wall then trying to make a turn. One last thing think about putting a pumper carb- on. Think Tilson or Mikuni. Hope something might of helped. Hold on tight. Happy Trails.