pwk vs. pwm

Vic Madrid · Posted: Thu Jun 08, 2006 12:34 pm Post subject: pwk vs. pwm

seeing as how my local competition seems to be improving by leaps and bounds (awesome Very Happy

), I'm trying to decide if making a carb change will help me keep up. Any thoughts on PWK vs. PWM? Right now I'm running a 41mm PWM pumparound. Looking for a 38mm (or smaller) but don't know which Keihin version would be best. Also, should I bother looking for another pumparound? How hard is it to convert a new carb? (especially if I have the old one to cannabalize the float bowl pieces, is it just a matter of drilling/brazing a tube?)

Motor is a Banke-built CR125, designed around a PI but now w/ stock CDI. (if that matters).

Any thoughts? Thanks!
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- Vic
- SCCA/WDCR F125 #54
- 2006 Tony//Kart Krypton 125

Andrew. james · Posted: Thu Jun 08, 2006 12:39 pm Post subject:

I gonna vote for 38mm pwm with no pumparound.

Mike Kline · Posted: Thu Jun 08, 2006 1:17 pm Post subject:

A 30mm carb and a one hole airbox will give you more than enough power Wink

From what I've heard and what little experience I have I dont think a pumparound is necessary for solo.
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#45 F125
2008 CRG Road Rebel

Brian Garfield · Posted: Thu Jun 08, 2006 2:44 pm Post subject:

As a completely irrelevant third party, I'm gonna have to agree with Mike Kline, he really seems to know what he's talking about...

I've got a 38mm you can try, call me.

Brian

Ryan D Thompson · Posted: Thu Jun 08, 2006 2:56 pm Post subject:

I've got a pwm pumparound but dont know the size of it. My motor is also banke built and now on oem cdi(which appears to be making more power than the dynatek pi I had). I'm not sure if its the motor/carb or pipe, but its got a great powerband from about 8500 to 13200 rpms. The pipe is pretty long so that could have something to do with it, but its pretty easy to drive and still get in the powerband.

I would keep the pumparound. I just love how easy it is and no mess with running fuel lines all over the place.

Vic Madrid · Posted: Thu Jun 08, 2006 3:46 pm Post subject:

Ryan D Thompson · Posted: Thu Jun 08, 2006 4:03 pm Post subject:

Yeah I'm running 2 base gaskets. Also are you running any spark plug spacers? The previous owner wasn't and once I pulled the head off and measured I needed almost 3mm of spark plug spacers to even out the plug with the top of the cylinder head. Hope that helps. Fastech-racing also has custom base gaskets of different thicknesses if you need to shim it a bit more to resist detonation. I haven't measured the squish depth yet in my motor so I'm not sure how close on the tolerances I am right now.

Vic Madrid · Posted: Thu Jun 08, 2006 6:05 pm Post subject:

Larry Andrews · Posted: Thu Jun 08, 2006 11:00 pm Post subject:

PWM - shorter between back of slide and end of bore, less intake tract volume. Best for absolute maximum top end power. The bowl section on the bottom of the carb sticks down pretty far and the main jet bolt rubs on the cases with many intakes. The two screws that hold in the upper cap seem to strip out at the absolute worst possible time.

PWK - longer, more intake tract volume. More of a midrange carb than the PWM. Fit is generally better and it's more foolproof to work on. A little bit more forgiving for jetting. I like that the idle air is adjustable by turning a screw that raises the slide...easier to get right as you can adjust both the fuel (pilot jet) and the air at idle without messing with the choke.

Pumparound. Biggest advantage (IMO) is that you KNOW when the carb bowl is full as fuel will be pumping through the return line. Makes starting the kart much easier in most cases. Powersource will convert any carb to pumparound, takes a few days. Ask for Neil but be prepared to spend some time on the phone...he likes to talk. A lot. Very Happy

BTW, he's great help with jetting questions also!

Bob Monday · Joined: 21 May 2004 Posts: 91

I have several carbs and agree with Larry that the PWK gives torque at lower RPM than the PWM. I attribute that to the longer intake tract.

I don't think that the pumparound makes any difference if you have a return line and everything is balanced out, but I began having problems with my non-pumparound setup and converted it. End of problems.

As for carb size, I find that the smaller (38mm vs 40mm) carb is easier to start, not as ON/OFF in nature. The 40mm has more top-end, less low-to-midrange.

Bob