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.
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?
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.
Last Edit: Jun 11, 2011 14:13:00 GMT -5 by 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.
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..
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.
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.
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.
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, 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.
Last Edit: Sept 15, 2011 14:06:58 GMT -5 by grizld1
r80rt: :)This is a splendid write up, THANK YOU!!!!
Dec 26, 2015 16:54:05 GMT -5
mashermoto: What the what is this shoutbox for? Or should I shout, WHAT THE WHAT IS THIS SHOUTBOX FOR!
May 12, 2016 22:22:21 GMT -5
motormike: Good Day ...just a FYI.. Wild Cat is this Labor Day weekend. Still go'n on. A few 650's still make the scene. Various rides at different skill levels each day.. awards dinner sunday eve. BS in the park'n lot after dinner.
Aug 23, 2016 7:57:01 GMT -5
lsettle: First post in over 6 years!
Aug 28, 2016 19:45:17 GMT -5
kardon: Wow quiet here, where did they all go.
Oct 7, 2016 2:18:13 GMT -5
gggGary: XS650.com LOL
Feb 16, 2017 20:49:02 GMT -5
buell88: Anybody have any idea who built the xs650 tracker used in the Draggin Jeans Ad on Pipeburn?
May 16, 2017 16:24:09 GMT -5
joshua: The regulator/rectifier unit I got from Mikes PMA has closer hole spacing than original. Are we supposed to mill the holes to fit?
Jun 7, 2017 19:25:58 GMT -5
joshua: My bad. I found the bracket they supplied to mount the rectifier/regulator... Uh oh. How is this meant to work? Which way is it meant to mount? Looks like I have to use some spacers or something. Good instructions would be nice.
Jun 7, 2017 22:09:52 GMT -5
craig8johnson: Not sure if this is the right spot or not but oh well...
Jul 11, 2017 18:04:15 GMT -5
craig8johnson: I'm checking the charging system. I'm afraid I might have fried the last battery. With the solid state regulator (after market) what should it be charging at. The book says, I think, 15 volts. I'm hitting 17 when revved. Is that too high?
Jul 11, 2017 18:06:19 GMT -5
gggGary: Yes 17 volts is too high, about 14 volts is max, sounds like you don't have the right regulator or it's wired wrong.
Jul 13, 2017 6:54:33 GMT -5
dean: Just saying Hello, new member who is going to fix up a 79 XS650 that has seen its better days. I will definitely have lots of questions coming up.
Jun 23, 2018 16:45:32 GMT -5
tt650: Trying to breathe life into a 1980 that's been stored (indoors) for 25 yrs. Air filters are dry rotted. Have cleaned carbs but she only runs briefly on choke then stops. Need jet setting info and other ideas that might help her idle and rev.
Jul 3, 2018 19:15:19 GMT -5
trix13: Hey everyone! New to the forum and am fighting those gremlins!! New charging system, ignition switch, coil and fuse box. Resistance is higher than normal on the ignition pick up so I'm trying to find one. No such luck yet.
Aug 16, 2018 8:50:48 GMT -5
trix13: Also, even though all of my connections are clean, I cannot seem to find out why , when at higher rpms, I hit the signals and the rpms pulse with the signals...hahah. same with the brake light. I appreciate all input!!
Aug 16, 2018 8:55:08 GMT -5
bob99: how do I post a question. I am new to the forum
Jun 6, 2019 10:52:10 GMT -5
adlpc: Hello all! Been enjoying your edifying posts and discussions - and as a fan of the XS650 since my early teenage years happy that I now own a 1980 Special which I plan to turn into a vintage half faired racer. Thank you all for being here!
Oct 1, 2019 0:58:56 GMT -5
jimothyj: Hello everyone, I just joined & wish would have known about this site in 2014 when I brought my 1974 TX650A back from the grave. I have spent a good deal of $$ and alot of time on it. Just painted it and working on electrical, I will post pics soon,
Apr 10, 2021 2:14:13 GMT -5
louisvan: trix13 - I had a problem with my 1975 SX650. When I got to highway speeds, the engine lost power. The problem was in the connectors. At a certain vibration and the wind pushing on the wiring loom, the connector lost continuity. A bad crimp to the wire.
May 20, 2021 1:19:09 GMT -5