Dels v Mikuni

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The SF2 that I am assembling has a flowed head and 5C cams. So far, no carbs. Has anyone tried Mikuni TM (in perhaps a 36MM) on an SF? They are simple and cheap (maybe $175-225 ea), available with or without pumpers. They were the hot upgrade on Harley XR1000's (that were delivered with Dell's) back in the mid to late 80's. WOT performance is great- XR750 flat trackers ran them. I don't have any info about their low/mid range performance.
 

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Can't speak for Mikunis, but they look like flat slides, which should mean a smooth bore and if they offer anything like Keihin FCRs then midrange would be very strong. That's incredibly cheap for a flat slide. I run 39mm FCRs on my overbored 880 SF based motor and new they would be worth a couple of grand for a pair. Miks are cheaper but US$175 is bloody cheap. Redax in Brisbane Australia has loads of experience with Mikunis.
 
Based simply on carb sizes attached to various bikes of similar size I've owned, 38mm carbs seemed big to me for a 750, but at least on the Paso they worked great. Following a somewhat irrational desire to return the Paso to original I refitted a Weber 2-barrel, which once properly dialed in works great. But honestly, the Mikunis were better.
 
I have run 39mm (FCR Keihin) without pumps on my SF2 with 5C on the road and they were fantastic. Running 5C you should make sure you have about 9.5:1 compression, all the standard later big valve head SF I have checked have had about 8.5, or it will be pretty flat in midrange. I bought the Keihins from someone who was advised by their tuner to downsize to 35mm because it was impossible to set up the "way too big" 39mm, but I found it easy to get them working fine.
 
Tippie said:
I have run 39mm (FCR Keihin) without pumps on my SF2 with 5C on the road and they were fantastic. Running 5C you should make sure you have about 9.5:1 compression, all the standard later big valve head SF I have checked have had about 8.5, or it will be pretty flat in midrange. I bought the Keihins from someone who was advised by their tuner to downsize to 35mm because it was impossible to set up the "way too big" 39mm, but I found it easy to get them working fine.
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I am running Ross Racing 10:1 pistons. Hoping not to sacrifice low end tractability, hence the thought about going with 36mm, but I am open to being corrected. And,... FCR's do seem to be the best readily available carb, but I am feeling kinda upside down on the project. Thanks.
 
I have no first hand experience with the TMR, but do think that they should operate a bit easier/lighter and maybe even a bit more controlled on the throttle due to the rollers that the slider goes up and down on (even less resistance) . Also, the wear shall be reduced compared to the RS on the slider guides due to the rollers. TMR do have a fully adjustable acceleration pump which I think the RS do not have (but might be wrong here), which would give another option to adjust to a more precise operation. They are more expensive though and you need to check if it's worth the extra money for you. For sure the best carbs on the market still for maximum performance from my point of view.

HTH
 
What's a TMR, Lothar? Did you mean FCR? I know the Keihin FCRs run with rollers for the slides. Didn't know about a Mikuni having that.

On the topic of accel pumps, my 39mm FCRs have them disconnected from throttle operation. I use them for starting only from a lever on the bars. i've noticed zero problems not having them.
 
CDHE said:
but I am feeling kinda upside down on the project. Thanks.
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Go for it. All these carbs are good.
Lothar are you sure Mikuni have rollers like the Keihin? I checked parts diagram for TM and RS, couldn't see rollers for the slides. It obviously isn't a problem though.
 
piranha-bro2 said:
What's a TMR, Lothar? Did you mean FCR? I know the Keihin FCRs run with rollers for the slides. Didn't know about a Mikuni having that.
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No, I meant the Mikunis. They have different ones:

RS: "budget" flat slide carbs with sliders sliding in a passage; no rollers, no adjustable accelerator pump. More than enough for street usage and a big improvement over the Dell'Ortos in any regards.
TM: originally designed for two stroke engines but can be used on 4-stroke, too, with the right jetting
TMR: the top end product of 4stroke engine carbs with steel rollers, choke, adjustable accelerator pump etc. Great to get the last bit out of your engine and improve even further the forces needed to open the carbs etc.
TDMR: same as TMR but layout as downdraft carbs (for very steep inlet angles, not usable on our bikes).
TMX: High end 2-stroke carb for racing applications mainly
HS & HSR: Harley single carb kits
VM: round slider carbs with modern design. usable for certain race classes, where flat slide carbs are prohibited.

So - basically, for Laverda there are RS or TMR, both in 36mm, both configured for Laverda available at Steven Topham in Germany f.e., and I assume there is a reason for that:


Price-difference between the TMR and RS are 400€. Your choice ;-)

Regarding the acceleration pumps used for starting: Do yours not have a choke system?!? Mine do...
 
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Tippie said:
Go for it. All these carbs are good.
Lothar are you sure Mikuni have rollers like the Keihin? I checked parts diagram for TM and RS, couldn't see rollers for the slides. It obviously isn't a problem though.
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The TMR do have them, potentially the TM not?!? Would explain the R as Rollers then...

See the pic of the slider on page number 3 (the forth from top); the rollers are in the steel cage left and right of the slider:


EDIT: just looked up the TM manual: the TM do NOT have rollers, the TMR DO have them... The TM also look very similar to the RS, the TMR do look completely different. So - my assumption seem to be right that the "R" is for rollers on the sliders
 
and yesterday the Twisted Twin was started for the first time

first start, settled straight into an idle, still need to balance the carbs but are close

we only run new engines for 10-20 seconds on initial starts for at least 10 starts letting engine cool in between
in this next clip we are now running the engine for longer and giving it some revs
 
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After the second clip finishes, up come Molly Tuttle and Rockabilly festival dance floor dancers!.... well it does here, not certain elsewhere on the globe... there is a 79 Jota going to a large rockabilly festival, with car show, suspect not many hot rodders have heard a Jota can'ed, 4c coming into the show parking lot... photos and vid will follow... j
 
redax5 said:
and yesterday the Twisted Twin was started for the first time

first start, settled straight into an idle, still need to balance the carbs but are close

we only run new engines for 10-20 seconds on initial starts for at least 10 starts letting engine cool in between
in this next clip we are now running the engine for longer and giving it some revs
Click to expand...
Mods: please move this post to “Music in the Shed”
😁
 
Received the Mikuni TM-40's, and there's an interference between cable insert and frame. Probably S.O.L.'d, but I am putting it out there in case someone has a clever workaround. Thanks again!
 

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