KLX330S - Bill Blue Mikuni TM 33/34

Discussion in 'Thumpers' started by motobene, Jan 15, 2020.

  1. motobene

    motobene Motoing for 49 years Supporter

    Mar 9, 2013
    Wichita Mountains SW Oklahoma
    This thread will document putting a modified TM33 on my former bike, a 2006 KLX330S with stock KLX300 exhaust and Larry Roessler woods cams. It will take a while to fill out the details as this is no longer my bike but my son's and he lives 10 hours from me.

    Here he is a little south of home beside his 'new' bike near our camp above Sargent, CO last year:
    2019 Leo on Kermit Near Camp.JPG

    I really loved that bike! Quite capable. I'm glad he has it now.

    So why give up on a well jetted Keihin CVK? During the Sargent-area ride I was on my flawless running 2019 Beta 390, and my son on the former bike. It was running... OK, most of the time (this is a link to a video):


    But it was inconsistent, and when it would start acting up, both bogging and blubbering. The really technical sections with a lot of interrupts and jostling got frustrating for him.

    I've been into this carb many times but I was scratching my head. I wrapped stretchy electrical tape about about 1/4 of the slide spring's height to stiffen it and keep the slide from riding too high and over enriching the mixture by positioning the needle too high for fuel demand. Ran like absolute gangbusters for half an hour, then the evil returned. Very distracting:dirtdog Something else was going on. A carburetor problem was consistent with the symptoms.

    So many months later, when my son said, "Let's do another ride this year", I was NOT wanting to be into that carb... again. I decided to look around for an alternate carb for the KLX.

    Pumpers are generally the go-to solution, with the Keihin FCR mentioned often. I knew Bill Blue out of Wichita, KS knows a lot about these bikes. I have had his 330cc kit on the bike for years. Bill still rides a 2006 KLX with his 351cc big-bore kit. So I called him. He reported selling 900 or so of his modified Mikuni TM33 pumpers!

    I was all in for a developed solution. $412 and it arrived a week later.

    Some photos. Note the custom work on engine- and airbox-side spigots. Also the custom fuel screw with cross pin so you can adjust with fingers. He calls this a TM "33/34" because when doing the special spigot bits he also cleans up the bore to match the KLX intake. He says flow-wise it acts more like a 35mm bore carb.


    This is a big carburetor! Not as bulky as a big FCR, but still bulky compared to the more compact stock CVK. Since I don't need and will not use the second throttle cable (gone from the bike long ago), I'll cut off the half of the throttle cable attachment for it. The ear just under the throttle cable mount in photo two... bye bye. Anything to pare the big thing down....

    I don't know the jetting yet. I'll have to take the carburetor apart to determine that. I asked him to baseline it at 5,000 feet of altitude.

    Installation and initial setup will happen when I can get to it.

    Bill warned to not run this TM with the airbox cover off. He says it won't run right and I'll tail chase in the jetting. Check. I already put the lid back on because to reduce irritating intake roar (those with tinnitus will know). Bill also says while the rectangular opening without the snorkle works OK, he suggested the truncated snorkle from a KDX200.

    The snorkle (14073) is $40.
    KDX Snorkle.JPG
    Brtp4 likes this.
  2. motobene

    motobene Motoing for 49 years Supporter

    Mar 9, 2013
    Wichita Mountains SW Oklahoma
    Identifying info: Mikuni Corp Made in Japan 33 8102 L8 21

    This is a simpler carburetor than the Keihin FCR. I like simple, especially if the result is great (to be continued).

    Other than working on somebody's FCR one time, this will be my first more intimate motorcycle pumper-carb experience. I've been doing things with carburetors for half a century, but most of that has been with 2 strokes and non pumpers.

    I was nice to find the screws correctly tight, not mongo tight. They were dry, however, so I oiled all of them as well as the mechanisms.

    Years ago some brilliant person decided it was 'safer' (I'm guessing) to have two throttle cables:dirtdog While stupid friendly, two throttle cables are consider by many a savvy tech guy to be clutter, so the second one gets tossed, every time.

    As for the elaborate mechanism, why pull directly on a slide with a cable when one can translate linear cable pull to rotary motion then back to linear slide motion?:jive The only justification I can see for it all is to have a rotary-to-linear way to drive the accelerator pump. Bill already defeated the second throttle cable mount. I'll go one step farther and later cut off the half of the cable attachment wing for the second cable. Less to bump fingers against.

    The needle is buried under the linkage. I left this part alone other than oiling it, and called Bill to ask what needle is in there and what the clip position is. Bill said he uses the stock needle for the TM33 (P9) and stock clip position (middle of five). Through dyno runs he said he tried other needles and clip settings but came right back to stock.

    From left to right the main jet (140 as set up for 5,000 feet, usually 142.5) on the jet needle post, low-speed jet (40 as set up for 5,000 feet, usually 42.5), the choke jet (unknown side), and the fuel screw (1.4 turns out as delivered). I don't normally lean out low-speed jets for altitude and I find most carbs are jetted too lean in that circuit. This a pumper carb, however, so maybe the usual rule of thumb doesn't apply?

    I pulled the fuel screw out to check it out and to lube it. I found the typical spring, washer, and o-ring, which fortunately came out with the fuel screw:

    Bill has the fuel screws made by a company that doesn't precision aerospace work. An expensive piece but precision is required. fuel screw. If the fuel screw wasn't extended I'd extend it. Thankfully Bill does that for us.

    I studied the pumper mechanism. The pump pin driven off the throttle in the first 30% or so of throttle opening. There is no adjustment other than the spray jet that screws into the body and protrudes into the venturi bell area, as Bill says he doesn't mess with that. Here is the mechanism from the throttle to the zinc chromate plated steel pin that protrudes into the float bowl:
    [The float angle is skewed relative to the float bowl interface plane, but it's actually as expected, resting under its own weight perpendicular to the axis of the main jet/needle jet/slide.]

    Note the anodized aluminum piston for the pumper mechanism (tight sliding fit - no polymer seals), sticking up above the float bowl plain due to spring extension force. Once assembled the piston gets pushed way down into the float bowl piston bore by the push pin.

    As for the fuel circuit of the pump, a small jet on the pump-side of a ball check - that lets fuel in but not back out to the float bowl - allows over capacity of a pumping stroke to return to the float bowl while offering resistance to pump fuel through the other jet on the spray nozzle side the ball check. Both jets offer resistance on the return stroke of the piston to unseat the ball and refresh the fuel.

    Bill said some reported poor fuel economy with their pumper carb. Bill reports up 70-75mpg out of his own 351cc bike, on which he has long retained the stock 1.9-gallon tank (my son's KLX still has the stock tank too). He says fuel economy suffers when a rider wicks the throttle open and closed frequently due to the proliferation of full pumping strokes.

    Below is the pumper's piston and spring out of the float bowl. Sorry about the photo being sideways.
    Bitingdog likes this.
  3. Norty01


    Jan 30, 2014
    Raced against Larry Roessler back in the early 1980's, out in Plaster City. He's one fast rider!

    Oh, clean carb!
    motobene likes this.
  4. motobene

    motobene Motoing for 49 years Supporter

    Mar 9, 2013
    Wichita Mountains SW Oklahoma
    Don't know where Plaster City is. Sounds like a place to get drunk :-)

    Now that I know what's in the carb and I understand how it works, it's going back in the box to await a trip to Colorado to do the install. This thread will go quiet until I can report on the install and the results, particularly at higher altitude where the stock CVK carburetor would go insane.

    In the meantime, if any of you have observations or comments, please post them, thanks.
  5. motobene

    motobene Motoing for 49 years Supporter

    Mar 9, 2013
    Wichita Mountains SW Oklahoma
    Cleaned things up by cutting off the rest of the 2nd throttle cable crap: