PWK alky jetting

5943 Views 15 Replies 5 Participants Last post by carolina shaker, Jul 5, 2008

BBIII

Discussion Starter · Jul 1, 2008

Ok so if i where to get some 36mm pwks on alky that where setup for a 7mil stock cylinder how much of a difference would there be in jetting if i where to put them on a drag ported 350?

There is no jet size on the main jet but i know it is BIG.

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dajogejr

· #2 · Jul 1, 2008

Bolt 'em on...
I'd bet they're damn close.

Get a cheap set of index drill bits...unless you're on Lectrons, they can be your best friend!!!

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BBIII

Discussion Starter · #3 · Jul 1, 2008

Well i have lectrons but dont have the extra pj's yet and need to get my needles in for them.

I dont think the main will need to be drilled any bigger there already HUGE.

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dajogejr

· #4 · Jul 1, 2008

Bobby...regardless of how big the main is, keep in mind it can only flow as much as the dump tube. So a .125 main can only flow .122 if the dump is that big. it can work the other way, say .122 dump and .118 main....the main being more restrictive.

Pick or index out the dump so you know where you are. When you get close to .125 on the main, the threads get real thin....

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Kawiking

· #5 · Jul 1, 2008

i told u i dont know crap about alky ...

what is a dump tube used for.... any pics

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dajogejr

· #6 · Jul 1, 2008

Dump tube is the tube where the needle (bottom of the slide) goes into the fuel bowl, and into the main jet.

That is also where the main jet screws into. (On Mikunis it's actually removable)
It's also called the emulsion tube.

That needs to be drilled larger as well. I can't tell you what the factory ID is for that tube, but I can tell you you normally drill it out as big or slightly larger than the main. Ex. .122 dump and .120 main.

You can't replace that tube on a Keihin. So, go too big, carb is scrap.... Just like with gas jetting, higher elevations require less fuel.
So someone that runs .122 dump and .120 main at sea level could run .116 dump and .114 mains at high elevations (think Colorado, Wyoming, etc.)

The dump or emulsion tube's job is to, for lack of better terms, mistify the fuel charge into the cylinder. Mix air and the fuel for the incoming charge of fuel.

If you were watering plants, would you just turn the hose on full blast and soak one tiny area...or would you put the hose end on sprinkler or mist, so you cover more.

Similar...you want the fuel like a misty charge so it combusts more efficiently.

I know I'm not using the best terms or descriptions, maybe someone could help with the terms or wording, but that's the jist of it....

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BBIII

Discussion Starter · #7 · Jul 1, 2008

Ok dave i will see what it is @ tonight

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Kawiking

· #8 · Jul 1, 2008

should i send my carbs off to get set up for alky ? if hate to mess a set of carbs up.

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99banshee

· #9 · Jul 4, 2008

QUOTE (kawiking @ Jul 1 2008, 02:52 PM) index.php?act=findpost&pid=4273should i send my carbs off to get set up for alky ? if hate to mess a set of carbs up.
They should be pretty close.We usually run .120 dumps and 116 mains on a drag port treefitty or 4 mill.

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Kawiking

· #10 · Jul 4, 2008

4 mill cub ??

brian.. pm me ur addy again and ill prob just send u my carbs so u can set them up for me.. do i need biger bowls ?? i have a pingle.

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BBIII

Discussion Starter · #11 · Jul 5, 2008

I was told to get some bowls for sure and a pingle so i did.

I will hopefully have the shee running on alky tomrrow but we will see.

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dajogejr

· #12 · Jul 5, 2008

QUOTE (kawiking @ Jul 1 2008, 03:52 PM) index.php?act=findpost&pid=4273should i send my carbs off to get set up for alky ? if hate to mess a set of carbs up.

Send me your carbs, Rico. I will set them up for you.

Keep in mind, smaller motors need bigger jets generally...both my friends 4 mils (Shayne and JT) require a LOT more fuel than my 10 mm motor.

I might be talking out of my azz here, but I believe the longer stroke and/or bigger bore pulls more fuel out of the jet...so...smaller or shorter stroke motors will need more fuel via bigger jets than a larger/bigger stroke motor.

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BBIII

Discussion Starter · #13 · Jul 5, 2008

I was told the same thing dave, and i have noticed that with the 4 strokes also....kind of weird.

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carolina shaker

· #14 · Jul 5, 2008

QUOTE (dajogejr @ Jul 5 2008, 05:35 AM) index.php?act=findpost&pid=4561Send me your carbs, Rico. I will set them up for you.

Keep in mind, smaller motors need bigger jets generally...both my friends 4 mils (Shayne and JT) require a LOT more fuel than my 10 mm motor.

I might be talking out of my azz here, but I believe the longer stroke and/or bigger bore pulls more fuel out of the jet...so...smaller or shorter stroke motors will need more fuel via bigger jets than a larger/bigger stroke motor.
dajogejr you r correct ,the bigger motor has a stronger carb jet signal than a smaller motor. the smaller motor does not take more fuel. but because it has a weaker signal. it requires a larger jet for the fuel to be pulled out, by the weaker signal. and then you run into that with, super large carbs. they have weaker jet signals than smaller carb's

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dajogejr

· #15 · Jul 5, 2008

QUOTE (carolina shaker @ Jul 5 2008, 08:51 AM) index.php?act=findpost&pid=4563dajogejr you r correct ,the bigger motor has a stronger carb jet signal than a smaller motor. the smaller motor does not take more fuel. but because it has a weaker signal. it requires a larger jet for the fuel to be pulled out, by the weaker signal. and then you run into that with, super large carbs. they have weaker jet signals than smaller carb's

Back when I was running PWK 39's on my 10 mil, my jetting was a bit smaller than my buds and their 4 mils...plugs don't lie..

Where they were running .125 mains and dumps, drilled out wide open PJs...I could run .122 dump and .120 main, with about 3-4 out on the DM Superjet, and have plenty of fuel...

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carolina shaker

· #16 · Jul 5, 2008

thats correct your ten mill pulls so much more air threw the carb than a 4 mil ,it creates more suction at the jet . the smaller motor cant pull the same amount of fuel, be cause it has less suction at the jet. so it takes the larger jet for the fuel can be sucked up easer by the smaller motor

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