SuzukiSavage.com - Carburetor Shootout

DragBikeMike

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Re: Carburetor Shootout
Reply #75 - 10/03/20 at 15:42:02

Cool the way you repurposed the intake boot and used the section of shopvac tubing to extend the airbox nipple. I like it. By any chance, did you take any photos of your cable mods? Can you provide more detail on the cable mods. I know someone who might appreciate that info.

Keep us posted on the tuning. It will be very helpful to know how that goes.

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Kwarran YaBB Newbies Offline SuzukiSavage.com Rocks! Posts: 8	Re: Carburetor Shootout Reply #76 - 02/02/23 at 00:47:29 DragBikeMike, I went with the Mikuni VM38 carb, but I don't get something. I thought it's better to ask here than to make a new thread. What do you do with the vacuum line from the petcock? And when running the motorcycle you have to put the petcock on PRI? Because I noticed there is no vacuum line on the VM38 carb
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TheSneeze Serious Thumper Offline Posts: 1310 Northern Nevada Gender:	Re: Carburetor Shootout Reply #77 - 02/02/23 at 07:32:36 Switch your petcock to a genuine Yamaha Raptor 660 petcock (no vacuum feed), and plug off the vacuum nipple on the carb.
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ThumperPaul

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Re: Carburetor Shootout
Reply #78 - 06/10/23 at 12:47:00

Hey Mike. Incredible study here!! I have a question that is in no way urgent or terribly important and I know it's the weekend, but I do want to pick your your big brain and put it out here to share! If you could kindly respond when you get a moment I would greatly appreciate it.

I think you know I installed a PWK40 carb (knock off) on my bike (stock bike except for Jardine exhaust and air box cover removed). The bike is running quite well, but I'm getting poor gas mileage (like 40mpg) virtually regardless of how aggressive I ride be it in suburbs or highway. You may recall that I've rejetted several time and I'm running a #48 primary and #162 Main. I think you commented those seemed really big and I agree, but I'm really not running too rich (performance-wise is good throughout, spark plug check, exhaust pipe check).

After seeing your test results and especially CFM stats, and learning about the venturi effect, fuel atomization, and more than my novice carb-tuning brain can handle....

My theory/question: The PWK40 carb is just simply too big without any other engine mods (intake porting, cam, piston, valves, etc). I think I'm having to "jet up" really big to mix up enough gas with all that air to get the correct air/fuel ratio. I think I've basically force tuned a fat carb on the bike and gas mileage is showing the gluttonous appetite.

Your results for the Harley SS carb really got me thinking down this path.

Thanks in advance for your thoughts and expertise!!

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DragBikeMike

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Re: Carburetor Shootout
Reply #79 - 06/10/23 at 18:53:14

"My theory/question: The PWK40 carb is just simply too big without any other engine mods (intake porting, cam, piston, valves, etc). I think I'm having to "jet up" really big to mix up enough gas with all that air to get the correct air/fuel ratio. I think I've basically force tuned a fat carb on the bike and gas mileage is showing the gluttonous appetite."

I managed better than 50 mpg with the PWK38 on this carb shootout. If you go back to the section that tested the PWK it should give the exact data. That was with a hopped up engine.

On a completely stock engine, the PWK 40 averaged 55 mpg. This post provides the details on that test. Jetting was similar.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1625732492

For some reason, you are running much larger jets. I looked to see if I have any photos of your carb. I don't seem to have any. Possibly if you post a set of photos, we can figure out why you need those large jets.

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paulthebikeman YaBB Newbies Offline SuzukiSavage.com Rocks! Posts: 3	Re: Carburetor Shootout Reply #80 - 02/26/25 at 19:07:48 Total newbie here. My bike is totally stock. I just got the VM38 in the mail. Are the jets still the same if my bike is completely stock?
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DragBikeMike

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Re: Carburetor Shootout
Reply #81 - 02/27/25 at 20:09:12

You will most likely end up with a main jet slightly leaner than the #210 I used in this report. Most likely a #190 or #200. A lot will depend on where you got the carb from. If you didn't get the carb from Lancer, you should disassemble and check every component to verify that they are the ones I specified.

All of the jets and settings should be the ones I listed, but the main jet will more than likely need to be smaller. You will most likely also end up dropping the needle one groove. Take it apart, verify what parts you have (main jet, pilot jet, main air bleed, slide, slide needle, needle jet, etc.) If all the parts check out, install the carb and give it a whirl.

You can change the main jet and pilot jet without removing the carb. You can also adjust the slide needle without removing the carb. Dialing it in is easy.

If you are planning to run this thing with the stock airbox, you will need to provide more air by removing the plastic door on the right side and/or pulling out the snorkel on top. What sort of airbox setup do you intend to use?

You might find these old posts informative.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1621150483

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1625732492

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paulthebikeman YaBB Newbies Offline SuzukiSavage.com Rocks! Posts: 3	Re: Carburetor Shootout Reply #82 - 04/02/25 at 22:40:08 I really appreciate your input. The screws that hold boot that’s on the cylinder head are really on there. I can’t get them loose they are starting to strip
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LANCER

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Re: Carburetor Shootout
Reply #83 - Yesterday at 13:20:50

Do you have an impact driver that you can get to those screws to loosen them ?
The jetting for a 36mm Mikuni VM carb kit that I sold was typically set up with a #20 pilot jet and a #190 or #200 main jet. Mikuni’s designation for the 36mm carb I used was VM36-4, while the 38mm carb is VM38-9. If the carb you got is different from a VM38-9 then you got the wrong one, the inside parts will need to be changed as well as the pilot and main jets. The cost of replacing all the inside parts is basically equivalent to the purchase of the carb itself.

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