Anyone who knows something about Bike/Jetski Engines

[BIGSLVRXJ]

Does anyone know exactly what reeds are and where they go? I'm thinking about getting a set of performance ones for one of our jetskis but would like to know what I'm getting into before I buy them. It sounds to me like they have to do with fuel/air ratio sort of kind of...maybe?
This is the set I'm looking at....
http://cgi.ebay.com/ebaymotors/ws/e...&item=4532595636&rd=1&sspagename=STRK:MEWA:IT

Thanks,
Collin

 

[Gil BullyKatz]

They're your "valves" in a two-stroke engine....

 

[bchulett]

Back in the 70s, reed valves were incorporated in most Jap 2-strokes to control low rpm throttle response (fuel/air)... while enabling larger ports and induction for higher rpms. The last time I had a Jap MX bike they were located in the manifold between the carb and cylinder intake port...

The piston skirts actually serve as the "valves" on a 2-stroke ... unless you have a rotary valve.

Back in the old days, it was common to shave the piston intake skirt to squeeze more top-end out of a 2-stroke ... shave it too much and it loads up at low rpms---a good reason for reed valves.

Does anyone know exactly what reeds are and where they go? I'm thinking about getting a set of performance ones for one of our jetskis but would like to know what I'm getting into before I buy them. It sounds to me like they have to do with fuel/air ratio sort of kind of...maybe?

Thanks,
Collin

 

[MattBlackXJ]

The reeds are located between the crankcase and the intake manifold. It is important that they close tight. If your current ones are not worn out, (which they probably aren't) changing them won't make any difference.

Matt <--Vintage snowmobile collector

 

[DrMoab]

Matt <--Vintage snowmobile collector

Wanna buy a 1972 Artic Cat Cheetah? haha

 

[BIGSLVRXJ]

The reeds are located between the crankcase and the intake manifold. It is important that they close tight. If your current ones are not worn out, (which they probably aren't) changing them won't make any difference.

Matt <--Vintage snowmobile collector

Thanks for the help so far guys.So all you have to do is separate the intake manifold and crankcase and put them in? Also,it says on his auction something about "tuning," what kind of tuning is required? Any ideas?
Thanks again

 

[biscuitboy87]

two strokes are very sensitive to jetting (isn't everything though?).
usually "tuning" involves getting the most performance out of the fuel mixture.
the "reeds" are valves commonly known as reed valves as opposed to butterfly valves or ring valves.
for info do a search on boysen reed valves.

 

[bchulett]

Crankcase ??

I may be wrong and it's been a long time since I've owned a 2-stroke, I don't recall reeds being located in the crankcase. I always thought they were located in the cylinder intake port where the manifold mates up... but things change over the years.

Basic Two-Stroke Tuning

Since you're not familiar with 2-strokes, I suggest avoiding ebay and taking your watercraft down to a professional tuner ...

Thanks for the help so far guys.So all you have to do is separate the intake manifold and crankcase and put them in? Also,it says on his auction something about "tuning," what kind of tuning is required? Any ideas?
Thanks again

 

[BIGSLVRXJ]

Well I know some about 2 strokes but probably not enough. I've torn down and rebuilt a lawn mower engines but I don't recall anything called "reeds" in those. Since there is tuning and whatnot involved I guess I may not get them. Thanks guys.

 

[bchulett]

Like I mentioned, reeds became the "thing to do" back in the 70s ... not all 2-strokes required or employed them. For Example: Big Bore Singles like Maico, Huskvarna, CZ, Bultaco, Montessa ... etc. etc. etc.

As far as I know, the Japs started this with their puny short stroke, small bore engines... although eventually ruled the 80-125cc class events. Probably a wasted effort on a lawnmower...

 

[MattBlackXJ]

Well, all my engines w/ reeds feed into the crankcase. I just haven't seen one that didn't. These are on 1970s era Kioritz snowmobile engines.

 

[bchulett]

Maybe I've got my wires crossed ... again it's been awhile. I could have sworn my '77 RM250 had reeds between manifold and intake port. Then again, I'm relying on memory from 30 years ago ...

Basic examples:

Yamaha piston port w/o reeds...

Yamaha case port w/reeds...

 

[Sarge]

Well, all my engines w/ reeds feed into the crankcase. I just haven't seen one that didn't. These are on 1970s era Kioritz snowmobile engines.

Considering the reed valves being discussed are for the air/fuel mix, locating the vavles in the crankcase would work like....well, it wouldn't.

Sarge

 

[bchulett]

This thread started out with a simple question regarding reed valves on Motorcycle/Jetski engines... and somehow digressed to 30 year old snowmobiles, etc.

Matt is correct in his statements ...

I know nothing about outboards ... but if you look closely at the cutaway view of this Yamaha HPDI (High Pressure Direct Injection) 250HP 2 Stroke outboard, it appears it has case port reed induction that feeds into the crankcase.

If we digress any further, I'm confident someone can find another two-stroke anomaly.

 

[MattBlackXJ]

Yea, we are fairly off the original topic, but some things should be set straight.

I initially decided to add in this disscussion because snowmobile engines are VERY similar to jetski engines. They use similar design and technology, and some of them even interchange. They are a MUCH closer comparison then to a bike motor.

To Sarge, case reed motors use transfer ports to take the fuel/air mixture from the crankcase (where it enters though the reeds) up to the chamber. They definitely work.

I have taken some pics. The first is of a case reed 440cc twin. The second is of the bottom of a cylinder from this type of motor. As you can see, there is no intake port to the outside of the cylinder, only an exaust port. There are several transfer ports from the crankcase, which the mixture travels up.

Back to the original topic, if your jetski motor is a case reed like this one, the reeds are attached to a plate that is between the intake manifold and the crankcase, and you can see the plate in the motor picture above.

 

[Glenn B]

Regardless, the reeds serve the purpose of a 1 way valve, no? Based on size and strength of the reed, they let fuel in as the negativive pressure dictates. They also (to a point... do not believe me? Hold your hand in front of a two stroke carb when it runs... smels like gas eh?) attempt tp prevent the pressure and fuel from going back "out the in door".

But what do I know. I am a factory trained Yamaha and OMC-Johnson/Evenrude Tech... And yes, I have built two stoke motors from just a box of parts. Regardless, reed boxes are usually bolted to the crankcase, or sandwitched between the block, intake and Carb. Not too many other options.

If tuning is your goal, better be spot on. Goin lean will screw you. Going rich... aside from looking like an idiot, you will foul your rings with carbon. That will lead to stuck rings... a rig with stuck rings will not idle. Be sure, and do it right. No two ways about it.

 

[Sarge]

Ok, stand corrected on the case reeds. Never seen that before. Both do the same job I would assume, meter the introduction of air/fuel mixture and close to prevent the escape afterwards. Be careful adding performance reeds in order to match the intended use of the motor. Same as doing a valve job on a motor, match the flow to the intended use.

Sarge

 

[BIGSLVRXJ]

I did win them but I think I am going to have a shop put them on. The tuning sounds like a bit much to me quite honestly. I'll see what the instructions look like but I'm not sure. Thanks for the input and info guys.
Collin