Mikuni 38 Flatslides

grant · Posted: May 27, 2007, 7:05 pm Post subject: Mikuni 38 Flatslides

A friend turned me on to a pair of 38 flatslides and I am wondering if they will work for a stock 650. Can they be jetted down to work with a stock motor? It seems everyone is running 34's for stock and 36's or 38's for the bigger engine builds. Are there any advantages of flatslides over roundslides or vice versa? Should I stick 'em back on the bench until the 750 build? Any ideas? Thanks, Grant

xs1961 · Posted: May 27, 2007, 7:16 pm Post subject: Re: Mikuni 38 Flatslides

Not sure I know of anyone sucessfully using flatslides on an XS or any other '70's 4-stroke before...only time Ive used 'em is on my two-stroke racers & motocrossers...think they're possibly more suited to thirsty high-revving motors...lot of modern 'superbikes' use smaller flatsides, again they're all high performance/high revving lumps though..

ttmaniac · Full Member Joined: Dec 22, 2006 Posts: 468

I've been told that flatslides offer slightly superior performance than a roundslide carb. Have no experience with it myself, however I wouldn't fear jetting 38's for a stock 650. It can't hurt.....what is it gonna do? Be to rich? Big deal....pull em off. I've heard the same thing as 1961...they are suited to high revving types of motors. Well, the xs spins to 8500 or so...If I was in the market for aftermarket carbs, flatslides are what I would go with. Perhaps PRO-FLO could give you some insight to this type of question. Good luck....I hope they rock n roll.....that would really make the 34mm lovers angry...tough luck for them. Go for it. What is it gonna cost ya's? A couple of jet? You got nothin to lose!

grizld1 · Posted: May 27, 2007, 8:30 pm Post subject: Re: Mikuni 38 Flatslides

xs1961, TM-series flat slide carbs are rather commonly fitted to the XS650 over here--not nearly as often as the round slides, but primarily because of cost, not suitability to the application. Mikuni HS-series Harley carbs (hardly a high-revving application) are big RS-type flat-slide pumpers, and a pair of TM36/68 pumpers is sitting in my shed waiting for this winter's build.

ight wanta check fitment, Grant; the TM's tend to run tall in the slide tower. Overall height of the TM38 is 170 mm, and a lot of that is above the center line.

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Been running 38mm flatslides for the past ten years on my BMW R/90S with no evil side effects with the exception of a smoother power delivery from off idle to max RPM,that's if you'd consider this a evil chacteristics of flatslides Laughing

The 38s on a 650 would no doubt be an overkill effecting streetability where low to mid performance is most important rather than top end. The flow capacity of the flatslides would be more suitable for 750 and up where the increased bore volumes enhances a stronger vacuum signal offsetting the increase area of volume in the venturi of the 38 flatslides.....................Jack

grant · Posted: May 28, 2007, 7:15 am Post subject: Re: Mikuni 38 Flatslides

Thanks for the input fellas. The guy told me there were some mods (or de-mods) you could do to these carbs that makes them more 4-stroke usable. I'm just now able to kind of find my way around the stock carbs after more than 30 years riding these bikes and I'm not sure I've the brain power or patience left to start learning about the ins and outs of a different type especially if they are not a proven staple of the typical XS mods. That being said, if they fit and or work I'll post any info. Thanks again, guys, I appreciate the feedback, G

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