OKO 30mm PWK Flat Slide Fit rse reed valve

[6blueoval9]

If its 19mm and it works it should be ok is my guess.

 

[Sumsloppymeet]

I said screw it and just went ahead and purchased the 19mm from Zeda had a coupon anyways from when i picked up the bike and motor im just curious if it needs a certain length of throttle cable or what ive gone through 3 sets of different 1/4 turn handles with no real ones i liked im hopeing this one i picked up today is promising does anyone have experience with these??

 

[Frankenstein]

Isn't there a certain relation between the intake and exhaust sizes, like an intake can only be used up to a certain point compared to the exhaust, since you simply cannot get the same amount in as what is going out. If the gasses are expanding and burning the volume of what is leaving the chamber should be more than what has entered, if the exhaust can only allow so much out then what can actually be burned before reaching that limit needs to be smaller in volume, and so the intake size as it approaches the size of the exhaust will become more irrelevant regarding possible power output, you can only produce so much power before it has trouble actually escaping.. We are dealing with 2 strokes to bat it off so some backpressure is a requirement meaning we really can't just let it all leave anyway and to a certain extent can't make it leave faster than a certain speed, which slows down the more volume you force out..

I don't know if that makes any sense but as I mentioned several times in the past I've yet to see an engine that didn't have a smaller intake than what it did in total exhaust surface area regarding diameter of the headers. It's just because the volume of air in is going to be smaller than what will be going out.

I wish I knew of a math that existed that could describe that, I'm certain if you looked at the amounts of biproducts produced from burning gasoline you could calculate the difference in volume, knowing a bit about how quickly a pressurized gas can leave through a certain sized orifice would get you close to an idea.

 

[butre]

the ideal intake is the cylinder head coming off for the intake stroke, pulling in perfectly atomized fuel at a perfectly stoichiometric ratio before reseating itself and torquing itself down right as the compression stroke starts. in 2 strokes the main reason they make the intake port smaller is because that's where the ends of the rings go, right where the hole would be if it was larger. in a 4 stroke usually the exhaust is the smaller of the two, if they're not the same size.

 

[Street Ryderz]

Isn't there a certain relation between the intake and exhaust sizes, like an intake can only be used up to a certain point compared to the exhaust, since you simply cannot get the same amount in as what is going out. If the gasses are expanding and burning the volume of what is leaving the chamber should be more than what has entered, if the exhaust can only allow so much out then what can actually be burned before reaching that limit needs to be smaller in volume, and so the intake size as it approaches the size of the exhaust will become more irrelevant regarding possible power output, you can only produce so much power before it has trouble actually escaping.. We are dealing with 2 strokes to bat it off so some backpressure is a requirement meaning we really can't just let it all leave anyway and to a certain extent can't make it leave faster than a certain speed, which slows down the more volume you force out..

I don't know if that makes any sense but as I mentioned several times in the past I've yet to see an engine that didn't have a smaller intake than what it did in total exhaust surface area regarding diameter of the headers. It's just because the volume of air in is going to be smaller than what will be going out.

I wish I knew of a math that existed that could describe that, I'm certain if you looked at the amounts of biproducts produced from burning gasoline you could calculate the difference in volume, knowing a bit about how quickly a pressurized gas can leave through a certain sized orifice would get you close to an idea.

Your right the exhaust port will be bigger than the intake and a stock china girl exhaust port at the window is the equivalent circular dia of around 20.5mm and 23.65mm at the flange then if you just widen the port not going crazy the recomended 2mm per side brings it up to 24mm and around 27-28mm at the flange since the flange area shouldn't exceed 1.15 x the window area.So now you have way bigger port volumes than a 16-18mm carb can properly provide for also stock exhaust dia are not sufficaint to dispurse the volume the cylinder will pump through with the higher volumes.

 

[6blueoval9]

With the exhaust also acting to fill the cylinder why would the intake need to be bigger than the exhaust?

The stock ports can already flow way more air than the typical 14mm 15mm 16mm carburetors can provide but those small carbs work well at providing a measure of air speed velocity you wont get with a bigger carb without much increased rpm to take advantage of the volume.

A small block ford 5.0L H.O. cylinder heads can flow enough air to make near 300hp without any porting but it doesnt mean bolting on a 850 double pumper carb will make it faster..if anything it will hurt performance...The same applies to any style of motor including a 2 stroke.

If you want a narrow rpm band up high then go bigger but make sure you run at a much higher rpm than you did with the smaller carb.

Most riding these bikes are driving them on the street and want some low speed acceleration with decent fuel mileage and reliability..not super high rpm maximum power.
Personally im trying to combine the best of both worlds to create a happy medium and major porting with a big carb isnt in the cards to accomplish it.

Sometimes less can equal more.

 

[Street Ryderz]

With the exhaust also acting to fill the cylinder why would the intake need to be bigger than the exhaust?

The stock ports can already flow way more air than the typical 14mm 15mm 16mm carburetors can provide but those small carbs work well at providing a measure of air speed velocity you wont get with a bigger carb without much increased rpm to take advantage of the volume.

A small block ford 5.0L H.O. cylinder heads can flow enough air to make near 300hp without any porting but it doesnt mean bolting on a 850 double pumper carb will make it faster..if anything it will hurt performance...The same applies to any style of motor including a 2 stroke.

If you want a narrow rpm band up high then go bigger but make sure you run at a much higher rpm than you did with the smaller carb.

Most riding these bikes are driving them on the street and want some low speed acceleration with decent fuel mileage and reliability..not super high rpm maximum power.
Personally im trying to combine the best of both worlds to create a happy medium and major porting with a big carb isnt in the cards to accomplish it.

Sometimes less can equal more.

These are not a 4 stroke there is no constant vacume and the the vac pulse a stock engine see's might have 120 degress of duration so the velocity through the carb is a pulse wave with atmospheric presure in front of it making for ample flow,A narrow rpm band is set by the pipe not the port volumes and if you set your stuff up right you can get long drawn out power bands and good low end torque from incressing the cylinder fill efficiency and using a pipe that stages where you need it.On the street a pipe that stages at 6-7 grand is useless that means all your real pull is just before you top out and what I'd call a narrow power band,between the gearing and your pipe the engine it's self has to pull to the point the pipe stages so what makes torque on it's own Volume.I run on the street alot and travel all over, my set up on the street is running 2.39 final gearing and the only way I could be doing that and still out pull traffic and other bikes is to make real torque just out of the engine before the pipe and the high rpm.2 strokes dont like to be run screaming for long periods therefore you set it up to run in the sweet spot most of these engines it's around 5,700-6,000 rpm and at that rpm I'm doing 45-48mph with pull left until 7,500 rpm then it falls of the pipe and still will top out at 9,000 rpm as the gearing has been unloaded enough that the engine can maintain it.

 

[6blueoval9]

Im just saying over carburetion on any motor is bad for performance...there is still a measure of velocity to consider which can be the intake wave from a 2 stroke and exhaust helping it along.

Hog out your ports then put a 30mm carb on it and see how it runs...then try an 18mm carb and re test...tell us which you prefer.

Both are going to give you the same power as both can supply the air needs but the 18mm carb is going to feel alot more peppy.

So why is that?

What i find interesting is Arrow racing using a 16mm keihin carb on their performance engines with large reeds making big hp numbers..

I would never pay $1100 for a 9.5hp china motor but its interesting how small of a carb is used to make the power.

 

[Street Ryderz]

Im just saying over carburetion on any motor is bad for performance...there is still a measure of velocity to consider which can be the intake wave from a 2 stroke and exhaust helping it along.

Hog out your ports then put a 30mm carb on it and see how it runs...then try an 18mm carb and re test...tell us which you prefer.

Both are going to give you the same power as both can supply the air needs but the 18mm carb is going to feel alot more peppy.

So why is that?

My ports are hogged out to 28mm across and 16.5mm in height on the exhaust and 24mm across and 16mm in height on the intake and I ran it with an 18mm carb that wasn't able to support the engines needs it now runs a 24mm carb that matches the engines needs and that's p/p no reeds.Yes a 30mm is really big but not far off for some of the large reeds and porting some folks run these days.

 

[6blueoval9]

Arrows 7hp motor uses a 16mm carb.
Arrows 5hp motor uses a 16mm carb
Arrows street sleeper uses a 16mm carb

The biggest they use is a 26mm mikuni flat side for a 9.5hp all out race motor only exclusive to racers who swear to keep a level of secrecy about the motor..lol