Cool thread, I'm watching closely !!
Questions though, what bikes do the 36 and 40 come off?? Make, model years etc...
I was researching drz400 carb swaps and the second most popular swap is to use a cvk40 off a klr650, folks are reporting near fcr-mx performance at a third of the cost of a fcr-mx carb. It would be sweet if I could swap the same carb on both bikes I own...

 

The 36 & 40mm pumpers are both off the shelf new Mikunis. Apprx $270

 

Matty, the carbs are a generic 4-stroke model from Mikuni designed to be compatible with a lot of engines. The pumper and smoothbore design makes them superior to many OEM carbs and especially CV carbs as a general rule. CV carbs work well in the confines of emission requirements, but a good pumper carb is hard to beat for a dirt bike...or dual sport. I'm kind of surprised at those reports on the KLR650 CV carb on the Suzuki being so good. I've had 4 of those carbs on KLR's over the years, and they always struck me as utilitarian carbs at best, even with a good deal of tuning. Now, there's an application for Richard's 40mm pumper that I'd like to see on a KLR650. I've loved the 36 pumper on my KLX300 and wouldn't even think about going back to the OEM setup.

 

I've been delayed by a few things including perfecting a way to measure km/h as I cross the hwy "finish line"; a change in noted kph after a mod or carb swap is the best way to measure HP loss or gain, and it's more accurate than trying to start and stop a stop watch at exactly the right spot.

My upgraded technique is working well; having just video recorded my trap speed (as they say at the strip) in 2 runs and gotten the same results both times with the 36mm and the vertical divider in its throat installed. I guess the next step is to remove the vertical insert from the 36 and see if that changes the trap speed.

Next I'll test the CVK34 and retest the 40mm to see how the trap speed for the other carbs turns out compared to the 34.


(KLX Webcams are now $400!)

 

Yikes!!! glad I decided to pull the trigger when I did. Looks like a 20% increase across the board-times must be tough...

 

Interesting that the CRF250X Keihin carb's accelerator pump is apparently mounted in the center of the carb/under the slide and squirts directly into the intake port...no bouncing the AP shot off the needle as Mikuni suggests for their TM36/HSR40 pumper carbs.

Not to mention that's a hell of an AP shot! (or so it seems)





Vids

http://www.rickramsey.net/Movies/CarbSquirt.AVI

or

http://www.rickramsey.net/Movies/CarbSquirt.MOV

 

You know there is a way to caculate the carb size general requirements and oddly enough with a 250 redlining (peak HP, not max possible revs) at around 8300 the recommended size was 36mm, but going to 10,000 the size was 39, so the thought of having the big carb for mods that would bump up the revs for the peak HP would make sense.

A similar thing happens with the head pipe, for the 8200 peak the ID is around 1-1/4 (I think, lost the paper) and 21" in length, bump to 10,000 the ID goes 1-3/8 and 19" length.

These are generalities, but are relatively close from past experience I've seen.

Richard, what equipment is needed for the AF set up you use? What equipment and what expense? I'm curious. It seems obvious you can get closer in jetting than shooting in the dark. I'm curious about the cost.

 

I too am curious. ZW mentioned an Innovate product and I found this on Amazon for around $170.
Innovate Motorsports 3845 MTX-L All-In-One Air/Fuel Ratio Gauge Kit for Powersports

 

I am using NGK's AFX a/f meter which I chose over the Innovate for some forgotten reason. - And a couple O2 exhaust bungs from eBay.

Check around for best current prices

 

At one point my 36mm AP nozzle was pointing not at the needle but just to the left, and it ran very good. I am going to experiment with moving the squirt stream away from the needle a bit and delaying the pump shot until the slide is out of the way and see how it does.