Donate!
Welcome, Guest. Please Login or Register :: View Members
Pages: 1 2 3 ... 9
Send Topic Print
Evolution of a HotRod - Part 4 Carburetor (Read 1150 times)
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Evolution of a HotRod - Part 4 Carburetor
07/08/21 at 01:21:32
 
Evolution of a Hot Rod – Part 4 Carburetor & Air Filter (Revisited)

This is the fourth in a series of reports intended to document the results of progressive modifications to the LS650 engine.
 
Part 1 outlined the project, set the rules, and established the baseline performance values for a box-stock LS650.  You can find Part 1 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1620523526


Part 2 examined the airbox.  We improved performance dramatically with a few simple and inexpensive modifications.  It was a lot of bang for the bucks.  You can find Part 2 here.

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


Part 3 took a hard look at the exhaust system.   We tried a Dyna muffler and a hybrid muffler that I manufactured.  We also tried the larger Mac header pipe.  The exhaust modifications provided significant improvements in acceleration and fuel economy.   You can find part 3 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1623048749


Part 4 installs a performance carburetor and revisits the air filter.  As I tested the carburetor the air filter proved troublesome.  I was compelled to take another look.

What I am about to describe worked good for me.  If you decide to try this stuff on your own, you assume responsibility for the outcome.  If you don’t have the skills, don’t do it.  If you don’t understand something, STOP and get help.  Get a manual.  Read up.  Comply with ALL the safety requirements outlined in the manual.  Make sure you know what you are doing before attempting any of this stuff.

Let’s get started.

Back to top
 
 

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #1 - 07/08/21 at 01:23:11
 
As discussed in part 2, it’s all about air.  If you want more power, you need more air.  Logic dictates that a larger carburetor will allow more airflow into the engine, and that additional air should result in more power.  There are limits.  Get carried away with the carburetor and you end up with an engine that only makes power at very high rpm.  A 650cc single-cylinder engine should work good with carburetors around 34mm to 40mm.  A 42mm might work OK, but it would probably sacrifice a lot of low-end power for high rpm power.

The stock carburetor is billed as a 40mm carb, but it’s venturi cross section is more on the order of 35.4mm.  It’s a constant velocity (CV) carb, so it has a butterfly and throttle shaft in addition to the typical slide.  It probably flows about the same as a 34mm variable venturi carb (Mikuni VM, Keihin PWK, DelOrto, Amal, etc.).

One of the goals of this project is to build our hotrod on a tight budget.  With that in mind, I had been searching the internet for a bargain basement carburetor.  About nine months ago, I found a deal on Amazon that was just too good to pass up.  It was a Keihin PWK40 for $28 bucks.  I had no idea what to expect, but hey, $28 bucks????  I figured I could take the risk.  With shipping and tax, the whole shebang came out to $36 dollars.

https://www.amazon.com/PWK40-40mm-PWK-Carburetor-Carb/dp/B07M824BB2/ref=psdc_...  
Back to top
 
 

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #2 - 07/08/21 at 01:24:35
 
Exactly one-month later this box was at my front door.  Hmmmmm?  Japanese carburetor, Chinese box.
Back to top
 

PWK40_Shipping_Box.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #3 - 07/08/21 at 01:25:49
 
I’m not overly concerned about where it shipped from, or even where it’s manufactured.  For this project, I just want a carb that is cheap and works well.  So, I rip open the box and guess what, there was another box inside.  Gosh, I didn’t know Keihin and Sudco are located in China.  Somehow, I get the feeling that Keihin isn’t really involved with this carburetor, or Sudco either.
 
Right away I noticed that the box identified the carb as both a PWK38 and a PWK40???  For $28 bucks, I could dig either one.  Guess I’ll have to measure it.
Back to top
 

PWK40_Inner_Box.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #4 - 07/08/21 at 01:26:24
 
It says it’s “MADE IN JAPAN”.  Who knows, maybe it is.  Looks legit.  Remember, $28 bucks.
Back to top
 

Made_in_Japan.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #5 - 07/08/21 at 01:27:12
 
I opened the second box and was pleasantly surprised.  It looked top notch.
Back to top
 

PWK40_Inlet.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #6 - 07/08/21 at 01:28:14
 
I had previously tried a PWK38 Air Striker on my high-compression hopped-up Savage.  It worked great.  That one was also of questionable pedigree.   I figured I might get similar results with this standard PWK.  We’re putting it on a stock engine, so it should provide enough air and fuel.
 
Let’s take a tour of this mixmaster before we slap it on the motor.

The airhorn & venturi are all polished up.  It’s a nice big hole, but it ain’t 40mm.  It’s 40 at the outlet, but at the mid-point it’s only 37.4mm.  I flow tested it.  It flowed the same as my first PWK38.  So, it’s a 38.  No biggie.  Just keep thinkin $28 bucks.
Back to top
 

Air_Horn__Venturi.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #7 - 07/08/21 at 01:29:02
 
This thing is way lighter than the stock carb, and way lighter than the VM38 too.  That’s a nice feature.  It will reduce the stress on the rubber manifold.  From the left side, you can see that it has the standard adjustment screws for idle speed and mixture.  It’s also shorter than the stocker and the VM.  That provides a little extra room for maintenance.  It has a nice enricher knob that is easy to operate, and there’s a big drain plug that permits quick & dirty jet changes.  There are four bowl vent connections.  You won’t have any problem finding a convenient place to pipe up the vent tubing.  Cap off the ones you don’t use.  I’m not a fan of the forward-facing fuel nipple, but you get used to it.  Lovin that official Keihin logo and the Sudco sticker.
Back to top
 

PWK40_Left.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #8 - 07/08/21 at 01:29:36
 
On the previous PWK Air Striker, I couldn’t figure out where the main air bleed was.  I found it.  You have to remove the idle mixture screw to see it.  Unfortunately, it’s a fixed .075” air bleed.  I have some ideas on how to deal with that.
Back to top
 

Air_Bleed___075_2.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #9 - 07/08/21 at 01:30:35
 
On the right side, you can see the other two bowl vents.  The nipple on the bottom is the overflow.  That’s a “love it or hate it” proposition.  Either you love the idea of not flooding the airbox and crankcase when your float valve sticks, or you hate the idea of burning down the garage when your float valve sticks.  Always turn your petcock OFF when you shut down your bike (even for just a few minutes).
 
That spigot is smaller than the stock carb.  It’s a bit loose in the stock manifold, but it works fine if you use the correct clamp.  More on that later.  Note that it’s for racing only.
Back to top
 

PWK40_Right.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #10 - 07/08/21 at 01:31:28
 
The slide is unusual, sort of a cross between a round slide and a flat slide.  There are no markings on it.  I have no idea what the slide cutaway is or how to measure it.

Likewise, the needle has no markings.  Careful measurement confirms that it is very close to a DGJ or a DGK.  The throttle return spring looks whimpy, gotta pay attention to that.
Back to top
 

PWK40_Slide_Assy.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #11 - 07/08/21 at 01:32:08
 
There is a little contraption that threads into the slide.  You have to remove it to adjust the needle position.  The throttle cable hooks into the contraption.  There is a small nylon ring that locks the cable in place.  One nice feature is the cable end is captured.  If the swaged cable end comes off, it can’t run through your engine (always painful).
Back to top
 

PWK_Slide__Needle_Assy_2_001.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #12 - 07/08/21 at 01:33:01
 
This shows the nylon lock ring on the end of the spring.
Back to top
 

Spring_with_Cable_Lock.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #13 - 07/08/21 at 01:33:37
 
The float bowl has a formed o-ring seal.  Replacements are available on eBay and Jets-R-Us.  The brass tube sticking up is the overflow.
Back to top
 

Bowl_Gasket.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Evolution of a HotRod - Part 4 Carburetor
Reply #14 - 07/08/21 at 01:34:27
 
This shows the internal parts, float, needle & seat, jets, etc.  Standard Keihin jets fit perfectly.  There’s a baffle assembly built into the metering block.  It keeps fuel from sloshing away from the main jet under hard acceleration, cornering, or breaking.
Back to top
 

Float_with_Needle__Seat.jpg

Knowledge is power.
  IP Logged
Pages: 1 2 3 ... 9
Send Topic Print


« Home

 
« Home
SuzukiSavage.com
03/28/24 at 03:08:30



General CategoryRubber Side Down! › Evolution of a HotRod - Part 4 Carburetor


SuzukiSavage.com » Powered by YaBB 2.2!
YaBB © 2000-2007. All Rights Reserved.