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The TTR250 FAQ web pages -> TTR250 -> Carb stuff -> Fitting a Mikuni TM32 and a TM33
Post Info TOPIC: Fitting a Mikuni TM32 and a TM33
TT-R250M


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RE: carburetor size
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Obviously not getting fuel or the pilot jet is too lean.

Refer to my post above.

Jarrah



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bruns


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TM32 flatslide plus other carb testing
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Hi all, first post but have used the site for a while.

Thought I would add a little contribution to some carb mods I have tried. Bikes are 2003 ttr250 and 1994 ttr250 with staintune exhaust with silencer endcap in and hole in airbox side plus ground headers. Jetting specs may be off as Aussie fuel is in my testing a lot richer than other countries and I'm at sea level

On the blue one I found substantial response in low to mid by boring the carb oval to get rid of the teardrop shape, bending the pumper to come on right off idle and tsper off after 1/3rd throttle and the following tk jets

main 142

pilot 48

needle 1 richer

With this combo I ran 14 47 gearing and had wheel lifting grunt.

 

White one I have installed a 32mikuni flatslide non-pumper . 

First i tried the xr280 baseline jetting of 250 main, 45 pilot 6dh2 needle q2 emulsion tube, it was flat and fluffy with a small promise of power

I can't remember exactly what I ended up with but will have a look if anyone else wants to do it

From memory it was:

main 190

pilot  22.5

needle 6dh7 leanest clip

q-0 emulsion

This combo transformed the bike, more down low than the bored carb and way more in the mid and top, very responsive fast revving throttle feel and hard to bog out plus never stutters on rough ground, basically a very wide very linear  power curve. FWIW i went 32mm non pumper over 33pumper because in my experience pumpers over fuel to make up for too large a bore size, on old school tech bikes a well jetted smaller bore flatslide gives better low mid response with a tiny sacrifice up top to the 33mm. 

The needle or emulsion could still be leaner as it runs well on the leanest clip but it's so close as is I can't be bothered testing more.

Fitting requires a 2 stroke throttle tube and cable and I made spacers front and rear of carb as its a way shorter carb, these were just upsized exhaust pipe dremelled the fit and fitted with devcon or jb weld.

Hope this info helps someone, there wasn't much out there when I was doing it

 



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Cubber


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Wow - quite a first post, thanks. Welcome to the forum.

Martyn



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bruns


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Thanks Martyn, good to see the old ttr has a following. Mines a bit of a project to see how good a trailbike I can make out of it while keeping the longevity, tired of rebuilding ktm's ect, plus the short wheel base is a blast when it gets tight



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peteBLUEttr


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Welcome to the forum matey!

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bruns


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Update,

Did a bit more fine tuning, ended up with

q-0 emulsion tube

6dh7 leanest clip

12.5 pilot

air screw 1 turn out.

Airscrew now works in the range it should and after putting a 30mm hole in airbox sidecover the bottom to mid is fairly crisp. Emulsion could go a size or two down to get the needle back to the middle but its not too bad



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bruns


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Got more response from midrange with p-6 emulsion tube and 6dh7 on richest.



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mossproof


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Mikuni pumper carbs
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Found this article whilst pondering carb options for the 350 (sorry guys, still twiddling my thumbs waiting for Woessner to get their act together...)

Contains a post from a certain TTRFAN. That you Brian?

Does anyone have any further info? Think this TM33 pumper carb can be used  on the DR350, which is in the right ballpark?

http://dirtrider.net/forums3/threads/ttr250-stroker-mikuni-pumper-carb.21061/

 

I was actually trying to find out if there is a larger TK pumper when I came across it. Gone off the idea of chinese-built flat-slides.

There's always the FI option I suppose (might be cheaper and easier to set up too!)

I know there's a thread on here somewhere about the TM32, which is not a pumper iirc.



-- Edited by mossproof on Wednesday 28th of February 2018 09:26:31 PM



-- Edited by mossproof on Wednesday 28th of February 2018 09:51:16 PM



-- Edited by mossproof on Thursday 1st of March 2018 03:07:58 PM

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ttr steve


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Contains a post from a certain TTRFAN. That you Brian?

You been drinking cider???



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TTRfan


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mossproof wrote:

Found this article whilst pondering carb options for the 350 (sorry guys, still twiddling my thumbs waiting for Woessner to get their act together...)

Contains a post from a certain TTRFAN. That you Brian?

Does anyone have any further info? Think this TM33 pumper carb can be used  on the DR350, which is in the right ballpark?

http://dirtrider.net/forums3/threads/ttr250-stroker-mikuni-pumper-carb.21061/

I was actually trying to find out if there is a larger TK pumper when I came across it. Gone off the idea of chinese-built flat-slides.

There's always the FI option I suppose (might be cheaper and easier to set up too!)

I know there's a thread on here somewhere about the TM32, which is not a pumper iirc.

It certainly was me Simon!

Some TM32 info here http://ttr250.activeboard.com/t53141894/fitting-a-mikuni-tm32/

Brian



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Kaos


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That thread is actually about the TM33P, which is the pumper carb and goes on to include the TM32 non pumper as well. It's a great read, and I'm seriously considering the TM33P for mine.

 I've spent way too much money on it already to stop now biggrin no



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mossproof


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Also been studying carb-boring, particularly oval boring, where the low throttle position is less affected, but airflow is increased in the upper reaches, which might be what I'm looking for to give good bottom/mid range but let the top end breathe better for power. Just seems that the 'States is the place to go to get these things done

https://thunderproducts.com/carburetor-boring-for-optimum-performance/


Also came across Dial-a-jet adjustable jetting kits, available for ttr250. Thunder Products seem to talk the talk?

thunderproducts.com/product-category/carburetion/dial-a-jet/dial-a-jet-dirt-bike/

Every day's a school day, but damn this internet thing burns time!



-- Edited by mossproof on Thursday 1st of March 2018 03:08:28 PM

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petenz


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LOL dial a jet....
Re hash and old idea... didn't take of
in the 80..it won't fly now...



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Bikes... 06 TTR250 / 09 XT660R / 1977 Montesa Cota 348 MRR / 1979 Montesa H6 125 Enduro...

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KMAN


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I was looking at the Mikuni Oz site today.
They list a kit for the ttr250.

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Kaos


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Well spotted KMAN, that never used to be up on their site. They had info on the carb but not specifically for the TTR250.

Pasted off their website.....

Description
"Going fast has never been so easy. These carburetors have for a long time now been the popular carb of choice to fit to any 250cc or 300cc engine with allowable space, where chasing optimum increases in performance and power along with general smooth throttle response and ride-ability, with the nothing short of outstanding results when fitted to your Yamaha TTR250.

These Mikuni carburetors are compatible size matched for your Yamaha TTR250 air box boot and intake manifold rubber flange. For carb clearance the motorcycle’s top frame bracket requires a little material to be removed and the rear brake fluid reservoir slightly relocated by bending the mounting bracket. The kit comes with throttle cables and a 1/4 turn quick action throttle as the Yamaha cables come up short on overall length. There are jets provided where the pilot may require fitting if your engine does run a little rich and the new middle size main jet must be fitted with an additional one up and one down size supplied for perfect main jet size conformation when doing WOT test runs.

Climate, altitude and fuel density from different octane fuels all may have varying effects on final fine tuning as does cam, exhaust and cylinder head porting etc. For this reason we strongly suggest checking the tune as per the supplied instructions to maybe even get more performance than initially experienced.

This kit includes a TM33 -8012 carburetor, a pair of cables and qu With the bonus I've been after a quick pull throttle.ick action throttle, a pilot and three main jets for tuning."

I'm very tempted by this,have been thinking about it for my 263 engine for a while.

For the 350 you'd probably go bigger??



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KMAN


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If i can find a replacement jet for my standard carb i might try this later on

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Black8driver


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I've recently bored out my STD carb and going to try that first. I simply hogged it out with a die grinder and finished with sandpaper roll. If it doesn't work well enough I was going to try a dr350 carb next or Koso 32mm Chinese version of pwk kehin. I've used those with success before on other bikes.
Si

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leigh


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That's good to know......

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TTRfan


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RE: Fitting a Mikuni TM32 and a TM33
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Information on fitting a TM33 from Mark McConnell, Australia. Might be tempted for the 350 if I could find someone to port a spare head I have waiting

I use this one: https://www.mikunioz.com/.../yamaha-ttr-250-mikuni.../... (the red frame bike in the pics is actually my bike)

There is a photo of a head bracket that has white X's on it.... That's what needs to be cut off. But I had spares, so I just used two of the left sided brackets.

The airbox boot- not as tight as the TK carb, but not sloppy. It clamps in nicely. The carb came with a 127.5 main fitted- I put it up to the 137.5 that was supplied in the kit.... But I'm in Australia where the kit comes from.

Whatever pilot came in the TM33, I left there. The main that it was installed with was a 127.5. The way that I originally read the ad for the TM33, was that it came with a few jets either way of what is in it..... The jets provided as extras were 137.5, 140, 142.5. I opted for the 137.5 which got the WOT AFR at about 12.5 (near enough for me). Then looking through the rest of the rev range, I found that it was pretty good everywhere but 3/4 throttle, where it took a dive into being too rich for me at 10.5. There was a distinct stumble at that range when I stopped looking too much at the meter. I lowered the needle 1 clip position (clip now at second from top) which seemed to smooth that out.

 



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