I recently read a web page with some info about mods on the KLX250/D-tracker, provided by a Japanese guy. Among his various mods was the installation of a Mikuni pumper carb (TMR34). What was intresting and amusing at the same time is how he came full circle on the whole process.

He started his carb work by rejetting the CVK and pulling the snorkle, which they call 'butabana' (pig nose) over here. He raced circuit with his D-tracker, so the insatiable quest for power and response eventually led to installing the pumper carb. He posted a rave review of the pumper. Well, after 3.5 years of operating with the Mikuni, his racing had tapered off and his riding environment shifted to about 90% city communiting. He felt that the pumper was overly sensitive (more jumpy with throttle inputs) to operate in stop-n-go traffic...said it caused him to become 'mentally fatigued.' So what does he do?...he puts the CVK back in! BWAAAAHAHAHAHA!

He now has the smooth stable response of the CVK, but misses the snap of the Mikuni on occasion. I guess you just can't have it all, but it's not enough to steer my country operating self from plopping money down on a pumper this week. Might be food for thought for people who operate in more of an urban environment though.

 

makes sense.... but i wouldnt put the cvk back on....lol

 

Hey, the CVK is made for nice smooth throttle work. If you have a "nervous" throttle hand, you might want to think about staying with the CVK.

However, if you want "pop" in the bike, then go with the pumper style carb.

I'm impatiently awaiting the arrival of the jet selection that is coming my way. I want to see what this puppy will do when given the proper amount of fuel with all the air that's going through now!

Should be very interesting!

And most gratifying!

 

The pumper definitely does make it more jumpy, I can attest to that. But that's why we do it, right?

You get used to it though and learn to go real easy on the throttle when going slow or use a little clutch in combination so that the bike doesn't try and rocket out from under you. I saw a review in a mag for a throttle tube that has three inserts to control the leverage or rate on the cable. One of the inserts slowed the throttle pull down in the lower part of the turn which had the effect of making it take more turn to get the same throttle position, which in turn smooths out the throttle application. The nice thing about it was that the WOT position was at the same position, so it speeded up the pull at higher positions. That might be interesting to play with.

One of the other two inserts it came with did the opposite, i.e., one speeded up the pull down low making you quicker on the throttle when taking off. The reviewer said that one was great on the MX track, while the former was better on the trails. The last one implemented the normal usual pull rate.

I can't remember the company or product name, but I'll try and find it again. It was a bit pricey at around $75 if I recall, though.

 

Sounds interesting! Do you recall if it was also a 1/4 turn throttle? That seems to be a popular mod. I think Pro-Motion has a similar product, but their inserts adjust the amount of turn, not the rate of turn.

 

Hey, Marty. I should have mentioned this before, but the Mikuni jets are easy to come by locally in most areas. My Kawasaki dealer had every jet I wanted. Just tell the guys at your bike shop which carb you're using and they should be able to set them on the counter.

Of course, if you have the right ones on the way, it doesn't matter.

On the quarter turn throttle issue, I've held off. I'm thinking that I want a good spread from idle to WOT, rather than the less managable short pull. If I was doing motocross, it'd be great. I pretty much want a switch from off to on. Street and trail work require more finesse, thus the stocker works for me. Subjective, I know.

Shadetree
www.rideok.com "Bill's Garage" Check it out!

 

I don't think it was a 1/4 turn throttle. I'm pretty sure it was the normal turn distance for all three inserts, but it varied the rate either high or low on the throttle. You still reached WOT at the same turn angle regardless of which insert you used. I'll need to find the article to be sure on the 1/4 turn thing, though, but I don't think it was.

 

Yeah, I know very little about the subject, but seem to recall them being referred to a 'switch type' or 'switchable?' I know there are models where you can change an actuating cam to adjust your rate of change in select areas.

 

Shadetree,

I'm seriously thinking about ordering the Dynojet kit for that carb. It not only has jets, but a tunable needle. Might be useful

Here's what is in the kit:

1 Main Jet DJ124
1 Main Jet DJ128
1 Main Jet DJ136
1 Main Jet DJ140
1 Fuel Needles DNO308
1 E-Clips DE0001
1 Adjusting Washers DW0001
1 Plug Drill DD #5/32
1 Screw DS0001

I might need either the 136 or 140 jet to let me run at the power level I want to with the backfire screen removed, the YZ450F backfire filter in place and the airbox lid off.

I found one on Fleabay, but it being sold by the buttheads at Starcycle. I haven't heard a good word from anyone about those yokles. Still searching.

 

Hey, Marty.

I haven't had any experience with the Dynojets on this carb. A friend used their kit to jet his 06 DR 650 and got great results. It still took several combinations to get it right, but when he did, that bike really came alive.

I don' see a lot of benifit from the Dynojet kit on main or pilot jets, but having another taper of needle may be good for fine tuning from just off idle to midrange. Since you already have the others on the way, it may be worth a try using them first. I did notice that the kit tops out with a 140 main jet. I'm at 150 right now and am still running the stock pipe. My airbox is wide open with the mesh removed and no lid. Stock filter right now. It's just a tad rich with the 150 but may fall into place with an aftermarket exhaust. I'm worried about losing some bottom end with the large diameter header. I know that will help overall power at High RPM but what about down low? I'm looking at FMF's Q2 muffler only or the Muzzy full system. I want to keep it quiet. Sorry to digress there.

The problem with our bikes is that it takes thirty minutes to pull everything, swap jets and put it all together again. That's if you really hurry too.

Do you have an externally adjustable idle screw? It does look like the Dynojet kit has a "screw". I wonder if that's it? I'd like to have one for my bike. The idle speed is really sensitive. It's borderline too high sometimes, but when I lower it just a tad, it dies occasionally. That's what that screw is for, but I can't get to it with the carb on the bike. If you have one, where'd you get it?

I got an email from Bill, your carb guy. He can retrofit my carb for under 100.00 so I may send it in once the weather gets worse.
It looks like his inlet and outlet fitments are first rate.