Question about Keihin carb sizes

[99LRDblaster]

So I have a 35mm PWK I am putting on my Blaster and the outside diameters are 42mm and 59mm. The 35mm may or may not prove to me too big of a carb for me in terms of performance, but if I change my mind and step down to a 33mm PWK, what are the outside diameters of the 33mm? According to Keihin's site, they say the 33 and 35 have the same outside diameters on both ends, but I'm not exactly buying that unless the inside diameter of the 33mm carb is thicker therefore making it 33mm.

 

[Awk08]

thats too big and is gonna run lean no matter what size jets you put in it, due to the loss of air velocity, but we can recommend a good piston when that you fry that one

 

[99LRDblaster]

thats too big and is gonna run lean no matter what size jets you put in it, due to the loss of air velocity, but we can recommend a good piston when that you fry that one

Why is it too lean? A lot of people run the 34PJ and have no probs and I've heard the 34PJ's mic out at 34.8mm as it is already.

At any rate, even if it does prove to be too big for my tastes, I'm interested in determining the O.D. of the 33mm PWK if I fall back on to that, so when I make my intake manifold and get the reducer for the 35mm it won't be such a large difference in size that I can't just work around a modest difference in size.

 

[Awk08]

i'm just passin on what i've read, in the "jetting 101" or similar professionally written article
the bigger the carb, the less air velocity, the less fuel will be picked up as it passes over the jets, so no matter how big of jets you use, the air will be moving too slow to pick up enuf feul, give good emulsion, and give you the desired 12.5:1 air/fuel ratio
i don't know of anyone on here that has had success running a 35 on anything other than a bbk

 

[99LRDblaster]

i'm just passin on what i've read, in the "jetting 101" or similar professionally written article
the bigger the carb, the less air velocity, the less fuel will be picked up as it passes over the jets, so no matter how big of jets you use, the air will be moving too slow to pick up enuf feul, give good emulsion, and give you the desired 12:1 air fuel ratio
i don't know of anyone on here that has had success running a 35 on anything other than a bbk

Not sure if anybody on here has, but I've seen a few others with almost my exact same setup(same porter too) run a 35mm and it ran alright for them. Air velocity is relative to the engine setup you have. The main reason why 35 and up carbs are preferred for strokers and BBK is because there is a larger displacement and therefore a larger vacuum of air to be had within the engine and a larger carb compensates for that. 12:1 is the theoretically perfect ratio for 2 strokes, although it rarely ever occurs to my knowledge(might be wrong) as inefficient as most 2 strokes are to begin with.

All in all, when I slap it on and and run it, I'll know if it is running lean or is off. If so, I'll pick up a 33mm PWK preferably to replace it. Time to invest in more spark plugs.

 

[roadkill]

i believe phragle ran a 34? with a stock size jug but i might be wrong and if your getting rid of your old carb let me know

 

[99LRDblaster]

Well I have a 35mm PWK as it is right now. I think I know the physical differences. The 33 and 35mm PWKs use essentially the same carb body. All Keihin does is take the 33 and bore it out(it has a thinner venturi lining). Depending on application or what it came off of the slide and needle might vary but it works in both carbs because they are the same carbs. This is somewhat annoying as IDEALLY, I'd like to pick up a 33PWK and I just bid on one on Ebay, but at the same time, I'm contemplating sliding a small insert in the venturi end of the 35PWK I have just to make it a 33PWK myself. Decisions decisions.

 

[blasterfreek30]

i also ran a 34mm pj on my stock ported motor and it ran great...batt is still using a 34pj on his stock ported motor and its been 3 yrs and his bike still runs perfect

 

[Vootie]

I've run a 35 pwk on my stock ported motor for two seasons now, no problems...

 

[99LRDblaster]

I've run a 35 pwk on my stock ported motor for two seasons now, no problems...

You have a 3 mil stroker though. That added displacement makes a difference. How much of a difference....hard telling. I don't have all the jets, but I'll hook it up and see how it runs.

 

[motoman9911]

thats too big and is gonna run lean no matter what size jets you put in it, due to the loss of air velocity, but we can recommend a good piston when that you fry that one

Are you just saying 35mm is too big with no evidence to back it up with? You do know there are 125cc two stroke bikes that come from the factory with 39mm carbs?

 

[Awk08]

i do know that, mostly power valve bikes with modern cylinders, not our 1975 based cylinders

i'm just sayin nobody on here has had much success running 35's on anything smaller than bbk's,

 

[99LRDblaster]

Are you just saying 35mm is too big with no evidence to back it up with? You do know there are 125cc two stroke bikes that come from the factory with 39mm carbs?

I thought the same thing. I think the big thing is dirtbikes weigh less and quads need more power down low instead of the real peaky powerbands 125s typically have. They are tuned more for ripping and peaky power which doesn't translate well on heavier quads. You are both right to an extent. I:I

 

[Awk08]

see what carbs the aircololed, non power valved, 125's were running back in 1975,
as our motors basically are, and you'll see who's right

 

[99LRDblaster]

i do know that, mostly power valve bikes with modern cylinders, not our 1975 based cylinders

i'm just sayin nobody on here has had much success running 35's on anything smaller than bbk's,

The DT200 engine was powervalved and liquid cooled and ran a 28mm carb. The stock YFS200 can run a 28mm no problem and that's even with extra weight to lug around. Just sayin...

 

[con8quest6]

...ive run the pwk 38 from my kx 250 on my 4mil motor with no trouble at all before...and its only 215cc

 

[rtaylor15]

have you had a chance to see how this works for your bike yet? if it doesn't work out the way you want i will buy your 35mm i'v been looking for one for my bbk thanks

 

[99LRDblaster]

have you had a chance to see how this works for your bike yet? if it doesn't work out the way you want i will buy your 35mm i'v been looking for one for my bbk thanks

Not yet......I'm doing the 450R shock install right now whenever Ken's bushings come in the mail. Then I have to do a leakdown and compression test just to make sure everything is alright. If that all goes through alright, I'll widen the stock manifold and put the 35mm in......see how it runs, then will have to purchase jets for it to get it to the ideal jetting setup. It has the Keihin OEM jets in it right now which are probably entirely too rich for my setup. If it doesn't work out, I'll sell the 35mm and my 30mm modified stock carb and try my best to find a 33 PWK.......which are a ROYAL pain in the ass to find for a decent price since they were only on 1 manufactured bike to my knowledge and the rest of them are aftermarket sales.

 

[rtaylor15]

ok so gonna be awhile then lol either way let me know i can't find a gd price on a 35mm on ebay.

 

[99LRDblaster]

ok so gonna be awhile then lol either way let me know i can't find a gd price on a 35mm on ebay.

Probably be another couple weeks to a month depending if I need to get a top end gasket kit if I have air leaks......or if I find out I need a rebuild by surprise. X(

If you can opt for the Air Stryker model. Just keep looking on Ebay for them. A lot of bikes used the 35mm PWK like the Kawi KDX200 and a lot of others so when you do searches look for "35 PWK", "Keihin 35", Keihin PWK", KDX200 carb", etc. Most are lame buy it now auctions that cost a lot but every now and then there are legit auctions and they go for a reasonable price or there is a clueless person selling one for really cheap on buy it now.

Don't know the situation, but this seller is selling a 36mm and it looks reasonable........so far. He is dumb and didn't list the size in the description so it probably has scared away a lot of bidders, but I messaged him and he said it's a 36mm, so it might go cheap.
86 Honda 250R ATC Carburetor Carb TRX250R PWK Keihin - eBay (item 150561173838 end time Feb-16-11 17:36:18 PST)