tm 34 flatslide update

[timg]

After some good advice from original post I thought I would share the results. I had it jetted where it ran really well in mid and upper rpm range but lacked torque down low,which you really need if you like to get in the dirt (tt-flat track) so I contacted Mike at 650 central and he hooked me up with epo's @tpo's. I had to rejet after installion. I ended up with a 25 pilot, p6 needle jet, 6f9 needle. 190 main. After completion it has really good bottom end and midrange torque. It felt a little faster before but it was to pipey and to much wheel spin. Bottom line is performance is greatly enhanced. My advice is if you get performance pipes the 1 3/4 are little bit much for anything but drag racing, most of the really cool pipes are 1 3/4. So if you get them figure a little more for some epo's.

[grizld1]

Thanks, timg! Your baseline for the TM's is much appreciated, and fills a big gap. I'll "sticky" it for reference so it doesn't get buried.

I assume the main air correction is run wide open?

[timg]

Yes it is, mixture screws are 1 1/2 turns out. Still tinkering and that may not be final setting. I have a question about mixture? I've read several threads where people say their mixture screw is 2 1/2 turns out. I've never had a mikuni on any bike that would run properly in that adjustment. Are they calling 1/2 turns full turns or did I miss the boat somewhere?

[grizld1]

2-1/2 is a pretty common setting on the BS34 (note that the mix screw on those works in reverse to the VM and cable-top TM's). But right, on any other Mikuni carbs I've worked with, a setting as wide as 2-1/2 usually indicates a need for a pilot jet change.

But what I was asking was if you get better results with an air correction jet in the intake bell or with an open hole.

[timg]

open whole so far, but not quite finished yet.

[tschiffely]

Would TM34's be a good option for a stock motor, with electronic ignition and aftermarket pipes?

Is there a 2-stroke/4-stroke version of these or are they all the same?

-Tschiffely

[grizld1]

TM carburetors come in several flavors. The TMX series are dedicated 2-stroke pumpers. The straight TM flat slides, like the VM round slides, can be jetted for both 2-stroke and 4-stroke applications, but tend to be superior 2-stroke carbs and OK 4-stroke carbs. Mikuni also makes dedicated 4-stroke pumpers with the TM label on them. The TM36/68 and TM 33/8012 are both offered in the US, and a 34 mm. version is offered in Europe; substantial fabrication is needed to fit any of these to the XS650. A very nice 34 mm. 4-stroke pumper kit with all the fabrication done is offered at a very good price by Topham Mikuni of Germany.

IMO it's pointless to install aftermarket carburetors on a stock motor as a fix for OEM carb issues. For the reasons why, see the VM section of the Carb Guide.

[tschiffely]

Hmm.. Interesting stuff!

I do have some SERIOUS carb issues.. Don't have ANY!!

I'm doing a full build on a bike, and don't have any carbs as of yet. I'll run the bike with the stock motor for the next riding season, however I'd eventually like to do a full rebuild on the motor with over-sized pistons, a cam, some porting.. Nothing race status, but a nice & healthy street thumper.

With that in mind, how do you think a generic (non pumper) TM32 or TM34 would work on my motor? I'm sure that pretty pumper set out of Germany is priced accordingly, and doubt its within the budget parameters..

[grizld1]

The 34's will work fine with stock or modified motor. The Topham kit isn't as costly as you might think; the last quote I saw on it was around US $600, shipped.

[timg]

If i had it to do over I'd spring for the pumpers. The tm @ vm are basically 2 stroke carbs, difficult to jet exactlly right for all circumstances. The TM is a more difficult to get the slide in and out and jets are a little harder to come by.

[grizld1]

There's no such animal as a carburetor with mechanically lifted slides that's right for "all circumstances," timg; only vacuum carbs will compensate for atmospheric changes. I'd really like to see the results of hanging a pair of modern vacuum carbs with light flat slides on the old XS. Fitment wouldn't be easy, though.

[timg]

The reason I say that grizd1 is I put a flatslide pumper on my harley. It's so much easier to deal with than the stock cv. Very easy to dial in and works flawlessly throughout the rpm range.Overall performance was greatly enhanced. It was a little pricey but in my opinion well worth the money.

[grizld1]

Oh yeah, I hear you! Your carbies are similar to the TM36/68's that I run (would have gone for the Topham 34 kit, spent the same money, and saved a lot of fabrication time if I'd known about them). All of those carbs--HS, HSR, TM36/68--are variants of the RS (Radial Smoothbore) design--the most advanced carburetors developed by Mikuni before the advent of EFI froze carb evolution forever. There are upstream and downstream effects with tuning changes in any carburetor, but component effects are much more tightly isolated in the RS types than in anything else I've worked on, and much less time is spent on cycles of change and compensation; tuning was almost a straight and easy downstream stroll. The big surprise was that the accelerator pump had no measurable effect on fuel consumption as compared to the VM's--around 48 mpg average in mixed riding on a cammed 700 cc. motor.

[kscustom]

What position do you have the needle clip in?

[grizld1]

kscustom, I don't know if your question is for timg or me, but the bottom line is that you can't tune by somebody else's motor. For what it's worth, if you're asking about the TM36/68 pumpers, I run 17.5 pj's and 9EBY1 needles at 4th position.