SuzukiSavage.com - A Tale of Two PWK40 Carbs

TheSneeze Serious Thumper Offline Posts: 1226 Northern Nevada Gender:	Re: A Tale of Two PWK40 Carbs Reply #15 - 10/11/22 at 11:50:44 Yet another difference - the main jet is further into the float bowl on the two piece main jet carb - by .100"!!
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TheSneeze Serious Thumper Offline Posts: 1226 Northern Nevada Gender:	Re: A Tale of Two PWK40 Carbs Reply #16 - 10/11/22 at 12:00:49 The slide springs are also completely different as well. JFG carb .043" gage x 3.115" long x .600" outside diameter Fleabay carb .035" gage x 3.900" long x .566" outside diameter
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DragBikeMike

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Re: A Tale of Two PWK40 Carbs
Reply #17 - 10/12/22 at 11:43:18

Thanks for the pics Sneezy. Very informative. Your's is a very different beast.

Are you sure that there isn't an additional brass piece up inside your metering block? A piece like the item I show in reply #8. Theduderino said it fell out after he removed the long needle jet/emulsion tube.

I can see there are emulsion holes in the long brass tube. See the little holes in this snip.

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Re: A Tale of Two PWK40 Carbs
Reply #18 - 10/12/22 at 11:48:39

Those little holes are gonna break vacuum in the tube, so all bets are off on the size of your main jet, needle, needle taper, needle jet, etc.

Here is a tabulation of the various needles I have measured, but I'm not sure how useful it will be given how much difference there is between yours and a standard PWK. Would be nice if you could measure the two needles you have and post the measurements.

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DragBikeMike

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Re: A Tale of Two PWK40 Carbs
Reply #19 - 10/12/22 at 11:56:36

This is a chart of main jet sizes measured with pin gages. It may be useful since you are shooting from the hip on your main jet. I'm thinkin you should just put it on the way it was delivered and see what it does, then move forward from there. The emulsion tube will probably make it behave differently from a standard Keihin PWK38. Would be great if you could measure your actual needle jet and post the size. I have a feeling it's still up inside your metering block.

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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4408 Honolulu	Re: A Tale of Two PWK40 Carbs Reply #20 - 10/12/22 at 12:02:05 It would also be great if you could measure the size of your main air bleed. It's behind your idle mixture screw. You have to remove the mixture screw to see the air bleed. Mine is .075".
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TheSneeze

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Re: A Tale of Two PWK40 Carbs
Reply #21 - 10/12/22 at 13:23:49

I really need to get a set of pin gages. The only bummer is they come in sets, and the good set (the smallest) is .011" to .060". This would force me to buy the second size set as well. One can never have too many tools, right?

Nothing else "fell out" when removing my needle. I will have to go back in there to see if is just stuck in there? I already put it back together.

Both carbs have the same long brass tubes, with the same pattern of holes.

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TheSneeze

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Re: A Tale of Two PWK40 Carbs
Reply #22 - 10/12/22 at 13:28:33

DragBikeMike wrote on 10/12/22 at 11:48:39:

Those little holes are gonna break vacuum in the tube, so all bets are off on the size of your main jet, needle, needle taper, needle jet, etc.

Here is a tabulation of the various needles I have measured, but I'm not sure how useful it will be given how much difference there is between yours and a standard PWK. Would be nice if you could measure the two needles you have and post the measurements.

At this point, what is a "standard PWK"? We have clearly identified that there are differences with almost every one of these carbs people buy. How would you be certain that you are buying a "standard PWK", from any online seller? Shocked

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Every twenty minute job is a stripped thread away from being a three day ordeal.

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'86 LS650g Savage (parts bike)
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DragBikeMike

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Re: A Tale of Two PWK40 Carbs
Reply #23 - 10/13/22 at 12:21:08

Yes, it's a crap shoot. But if you have a carb (knock-off or genuine) that complies with the Keihin illustrated parts breakdown, then I define that as "standard" (i.e. faithful to the OEM design). The three PWKs I got were all pretty much faithful to the OEM design.

This link will get you to a good illustrated parts breakdown. Note there are no removable needle jets shown. It even has a note that cautions you not to try and disturb any parts not shown on the illustration.

https://www.jetsrus.com/carburetor/carb_keihin_PWK33-41_carb_exploded_view_pa...

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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4408 Honolulu	Re: A Tale of Two PWK40 Carbs Reply #24 - 10/13/22 at 12:22:49 My PWKs all had a main jet that looked like this. It is identical to a genuine Keihin main jet intended for a PWK.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4408 Honolulu	Re: A Tale of Two PWK40 Carbs Reply #25 - 10/13/22 at 12:25:16 Between the main jet and the aluminum metering block, there is a brass washer. It doesn't want to come out. You can see that the main jet threads into aluminum. There's no emulsion tube. The main jet goes directly into the aluminum metering block.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4408 Honolulu	Re: A Tale of Two PWK40 Carbs Reply #26 - 10/13/22 at 12:26:48 Way up inside the metering block you can see what appears to be a brass needle jet.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4408 Honolulu	Re: A Tale of Two PWK40 Carbs Reply #27 - 10/13/22 at 12:28:46 From the other side you can see the brass needle jet. It's fixed in the metering block. I suspect I could get it out, but I would most likely ruin the carb removing the needle jet.
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Re: A Tale of Two PWK40 Carbs
Reply #28 - 10/13/22 at 12:43:22

Of course, the relationship between the needle jet and the slide needle are critical to correct mixture control. There are no emulsion holes on what I define as a "standard" PWK. It's similar to a Mikuni VM. It's a simple port that connects the top of the needle jet to the air correction jet. My PWKs have a fixed air correction jet (main air bleed). That's faithful to the OEM design. Your PWKs have an emulsion tube and what sort of air correction? Those are drastic differences. It's gonna behave a lot differently than mine, and the main jet and needle selection will probably be very different from mine. Won't know until you try.

Are you sure the first knock-off you got has an emulsion tube. Your pics indicate a standard Keihin main jet in the first knock-off. Can't see how an emulsion tube would be held in. Got any pics of that first knock-off main jet and metering block, main air bleed?

This link might be useful. It's a selection of needles along with an explanation of how they measure the needles. It also shows the needle/needle jet configuration on a standard PWK.

https://www.jetsrus.com/a_jets_by_carburetor_type/needle_keihin_N427-48.html

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TheSneeze

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Re: A Tale of Two PWK40 Carbs
Reply #29 - 10/14/22 at 15:43:19

Based on your definition of a "Standard" PWK, the first one I received off Fleabay is a standard. With some crappy quality parts. The newer one from JFG Racing is the one with the holes in the emulsion tube. Both of my PWK's have the small pressed in brass piece just below where the slide stops. Here is the JFG Racing carb with the filed notch. It sits proud of the throat diameter.

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Every twenty minute job is a stripped thread away from being a three day ordeal.

'87 LS650h Savage Street Tracker (destroyed by fire)
'86 LS650g Savage (parts bike)
'81 Kawasaki KZ750e ELR tribut

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