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Discussion Starter #1
so i am taking my daughters 50 apart and doing a little maint on it... i have a question... what exactly does a reed valve do... this is more for my knowledge than anything.. i ahve always wondered what they do.. i know if they go out it runs like crap... but never actually knew what id does?

just lookin for a little info

thx aaron
 

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it acts like a one way valve for the air/fuel coming into the crankcase. it stops the air from being blown back out through the carb so the air is pushed into the combustion chamber instead when the piston goes down.

I hope what I stated makes sense to you...
 

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Here's a great link for understanding how a two stroke works.

http://www.vf750fd.com/blurbs/stroke.html[/b]

WOW i had no idea a pipe on a 2 stroke was so important!! also i would think keeping that pipe/exhaust clean from the gas/oil being spewed in there would be an important step in maint.



thx guys.. just had a little curiosity last night... alot of the time we work on stuff but never actually know what that part does or how it does it.. lol

thx for the link. later aaron
 

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the PIPE is the most important aspect on a two stroke engine....bar none....

similar to a camshaft in a 4-banger........

it is the heart of the engine and will ultimately determine the power band of the engine.....


like mentioned earlier....the Reeds are used as a 'one way valve'.... housed in a 'cage'.....usually (2) of them.... this lil invention is what has progressed the wider power bands on 2-bangers and was an EXCELLENT design...


before then..... we only had 'piston port' 2-strokes.... and if any of you were racing in the 70's....you know what I am talking about.... almost NO POWER BAND at all.....you were either 'on the pipe'....or you were stopped.....

dang I miss my 74 Elsinore....... NOT! lol
 

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the PIPE is the most important aspect on a two stroke engine....bar none....

similar to a camshaft in a 4-banger........[/b]
I would have to add that the porting of a two stroke cylinder is way more similar to a camshaft on a 4 stroke.
 

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Discussion Starter #7
the PIPE is the most important aspect on a two stroke engine....bar none....

similar to a camshaft in a 4-banger........[/b]
I would have to add that the porting of a two stroke cylinder is way more similar to a camshaft on a 4 stroke.
[/b]

how is that??? i thought the two strokes were a dome that you could interchange to up the psi theoretically pushing the piston gas faster.. (hope this is making sense) unless we are talking boring the intake /exhaust.. guess i really need to take one apart..

i am by no means an expert but i have been reading alot today about this stuff..kinda got the bug for a banshee now lol...
 

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2 strokes are all done with port heights. The higher the port height the more top end bias. I know when i was ridding 02-03 honda cr 250's we would deck the bottom the cylinder and mill the head to get the bottom end back(lower the port height)
 

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unfortunately.....on the 02 and later CR250's.....there was no cure for the Case Reed induction system.........im sure lowering the Exhaust port might help.....but most people opt to tune their 2-bangers with their pipe...... although you will hear pipes for 4-bangers advertised as low, mid, or high end pipes.....and this is somewhat controlled by the length and diameter of the header... shorter/fatter = HIGH rpm.... longer/thinner = LOW rpm..... (usually).... but, the effect of this type of pipe on a 4-banger has little effect, when compared to a 2-banger....you can literally lose ALL your top end....or ALL your bottom end.... simply by changing a pipe on a 2-stroke....... if you see a very FAT pipe on a 2-banger.....you can bet it has plenty of TOP END....if you see a longer/thinner pipe...you can bet its a Torque pipe......some of those new ESR top end pipes are so FAT they look like a basketball with a nipple on the end...lol

as for porting.... well, I will probably disagree on this being the key factor..... I still believe the Pipe will make/break your 2-banger... .but Porting.....can, produce damaging results if done by someone not familiar with 2-strokes...... but the same holds true for a 4-banger....I mean... you can really screw up your performance if you dont know what your doing...... on a 2-stroke...I would say the raising or lowering of the exhaust port is the most critical function........ so you dont wanna take much off of here...unless your really good...... which I aint...... but this does bring up another topic or 'food for thought'...... the exhaust port on a 2-stroke is so critical to performance...that many engine designers have put a lot of effort into modding this particular section......

from the old days of WTF...why does my 125cc piston port engine not have any bottom end.......(like...DUH)....

to ultra modern 'variable exhaust port techniques'...which come in many varieties..... like the older Rotax 'RAVE' cylinders....or any type of water injection device used on the older jet skis.... believe it or not....shooting water into the exhaust of a 2-stroke changes the performance DRASTICALLY....

do we have any 2-stroke porting experts that could give us a lesson on this?

I know John ports a lot of Banshees....(the traitor...lol)..... maybe he could help us out....
 
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