Reed Valve Help

Discussion in 'Performance Mods' started by Justinsavs, Apr 19, 2016.

  1. Justinsavs

    Justinsavs New Member

    Hey all! So I've built a Mongoose MotoDolo with a jackshaft kit... There are a few modifications I'm now looking at including Reed Valves and Boost bottles, along with maybe a compression head in the higher end future.

    Now for the problem. I ordered a reed valve intake, and I already have a boost bottle intake and bottle. But there is not enough space in the frame for the carburetor and intake/reed valve to fit. I cannot use either! Nobody makes intake ends that connect to the reed valve or boost bottle intake that can be "offset" from the intake. What is your guys' opinion?

  2. 45u

    45u Active Member

    Boost bottles are a total waste of money only thing they do is look cool. How many motorcycles 2 cycles come with them NOW? In the old days many new ones I do not know of any.
  3. HeadSmess

    HeadSmess Well-Known Member

    hard to see, theres one just behind the cylinder. its that black box with pipe to intake manifold.

    another one. not the stock one though.?

    banshee engine, has some sorta chamber that communicates with both intakes.

    another nsr... 250 twin.

    meh... if you understand how they work, can handle spending days testing various chambers... and really find your half-throttle tuning critical...
    go ahead and fit one to your engine.

    if you think they will add more power... they wont. they merely smooth out the mid range splutters common to most two strokes. which is why they are seen primarily only on road bikes. dirt riders tend to be on-off throttle. road riding needs more linearity...smoothness...
  4. danlandberg

    danlandberg Member

    If you are going to use both a boost bottle and Reed valve, the tube to the bottle(s) needs to be between the reed valve and cylinder or the bottle will not get the charge from back pressure. The reed valve minemizes back flow to the carb due to the reeds closing. The snappy response you get with a reed I due to fuel and air mixture atomization. It's like squirting fuel with a spray bottle (a fine mist), or delivering fuel with an eye dropper. As far as room to install, "fabrication" is all I can say. I'm thinking of running both myself, so, fabrication is in the cards. Good luck, and have fun building.
  5. HeadSmess

    HeadSmess Well-Known Member

    thats nonsense. they dont do it on factory engines.

    its the reversion pulse as the reeds close. air speeds up, gains momentum then suddenly WHAM. it basically hits a wall. what happens when you point a hose at a wall? you get a face full of water...or look like you pissed yourself.

    and yes, reed valve engines suffer from reversion just as much as piston ports and disc/drum valves. plain old physics. its usually not as bad as the intake manifold is much shorter. less air. less momentum. less "splashback".

    the boost bottle simply gives the air somewhere to go rather than try and squirt out through the nearly closed throttle. boost bottles do NOTHING at high RPM/full throttle.

    all reeds do is allow the crankcase to open earlier than fixed piston ports. more air and fuel gets in. and at low speeds, they prevent the crankcase squirting it all back out again.

    forget about reeds, forget about boost bottles, just fit a decent tuned pipe, as well as tuned intake manifold.
  6. Fabian

    Fabian Well-Known Member

    Reed valves are a very good system.
    Boost bottles are a complete waste of time and money.
  7. 45u

    45u Active Member

    I AGREE!
  8. Rob H

    Rob H Member

    If many of you feel reed cages suck so much why does every single production 2 stroke motor crosser come standard. I'll tell because the help recover lost power believe it!!!!
    Fabian likes this.
  9. Rob H

    Rob H Member

    A boost bottle is nothing more than an expansion tank for the fluttering fuel to go does anyone wonder why their air filter is oil soaked when the motors induction is sucking the air and incoming fuel charge in and not out
  10. Fabian

    Fabian Well-Known Member

    At very best, a boost bottle helps to improve the idle characteristics of a 2-stroke engine with aggressive port timing when the engine is idling, or put another way, when the throttle plate or throttle slide is closed. Outside of this scenario, the boost bottle is completely useless.
    Even so, a reed valve intake provides better idle improvement than a boost bottle can ever hope to provide, and it improves midrange torque, and throttle response. A reed valve intake is no longer relevant if peak power (and consequently high rpm) is desired, as the reed valve impedes air flow. The best option for that level of engine operation is a disk valve system, but it suffers heavily in the low rpm range and the transition between low and midrange power.

    There is a good reason why Honda used reed valves on the 500cc 2-stroke 4 cylinder grand prix racing bikes, and it wasn't for producing peak power.
  11. Frankfort MB's

    Frankfort MB's Well-Known Member

    I have an old rse reed for my HT but it didn't seem like it did anything, I run at full throttle most the time I ride but I have a lot of major hills to go up
    Should I put the reed back on and it not effect top end power?
  12. jaguar

    jaguar Well-Known Member

    Frankfort, click on my signature link to read how to modify the piston and cylinder to work in harmony with the reed valve for power increase.

    Check out the offset intake manifold at JNMotors which helps sometimes when there's no space for carb or filter.

    If there is absolutely no space to be had for a reed valve then just don't use it. You can lengthen the distance between cylinder and carb for more low end power. Also lengthen the stock exhaust.
  13. Fabian

    Fabian Well-Known Member

    Installing the reed valve without altering the jetting to suit the new combination will not give any power improvement. You "MUST" dial-in the carburettor to take full advantage of the reed valve intake system.

    The reed valve intake will not do anything to improve high rpm performance, but that is of no consequence as these Chinese 2-stroke engines should not be revved above 4,500 rpm for any period of time, and ideally operate in the 3500 - 3800 rpm zone; where the reed valve boosts midrange torque.

    If you want an example of massive increase in midrange torque, you should look no further than this example, with the engine tuned and tweaked to perfection, using a reed valve intake and Walbro (diaphragm) carburettor; operating in perfect harmony.

    Last edited: May 21, 2016
    Rebornsol likes this.