Dels v Mikuni

  • Thread starter Thread starter Davo
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Tippie said:
Lothar, don?t waste your energy trying to get people to change stuff like this. It is personal preference.
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you're right. I am not trying to convince him, he is trying to argue the invest to himself (or maybe to the misses...  :D). I don't need any argumentation, I was convinced when they guy that set them up called me to tell me "I found 10 HP - shall I search for more?"  :D

I am not that sure that top-end power does not increase with the Flatties. This is less so much the case just due to them having flat sliders but you typically increase the size of the carbs when going to flatsliders. Not that more throughput in a carb can generally put in more power, but as the 32mm Dell'Ortos are chosen just because with the more narrow ones it is easier to set them up and keep torque alive and not because they deliver most top end power, there are some HP to gain if you go bigger (and adapt the inlet manifolds to be tapered from 32 - 36mm f.e.).

In addition to that, keep in mind that with the Dell'Ortos (just as with any round slide carbs I'd say...), the biggest bore is where the highest velocity should be, which is contra-productive. The smooth bore carb has an advantage here, too, as it has constant air-speed from the entry to the needle/needle jet and on to the inlet (even increasing speed the closer you get to the valve if the inlet is still 32mm...). The Dell'Orto goes from 32mm (inlet) to 38mm (around the needle) to 32mm (to the head) with a lot of edges and causes a lot of turbulences. They were the best design 50 years ago when they were designed, how ever, things have been developed further and that is simply what the Mikunis and Keihins are: a "younger" design. Interesting that their design hasn't much changed also in the past 30 years since they first came out...  ;)

BTW: I can't proof it with a dyno print-out, but from the "butt-o-meter" if you will, the installation of the home-made power-blades have done something good on low end throttle response, too...  ;) But that may be just me arguing myself the invested time... not sure ??? For sure they haven't done anything bad, that's why I keep them...  ;)
 
Miks meter the fuel better and have a much lighter action.  No miracles, just an improvement, like fitting a Witt.  Won't turn the bike into a zzr1400 powerhouse overnight.
 
Peppone said:
Has anyone tried Mikuni TMRs instead of RSs?

Peppone
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Yes I have had them for about 4 years now, they are indeed (as Lothar says) fitted with rolller bearings on the slides, so no clatter at idle engine speed. Better mileage, easy and much lighter throttle pulling: full bore is only half the rotation, compared to the Dells. Best investment second to a full engine rebuild!

Hein
 

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I fitted a triple 36RS Mikuni set as supplied by Tophams, correctly spaced for the triple and jetted to my specs (which were supplied by Red, thanks again!).

These came with 2 return springs which made throttle action with the stock twistgrip just as heavy as stock Dellortos.  I junked 1 spring, altered the opening quadrant slightly and hey, presto, (lots) lighter pull with less wrist action.  Have never experienced anything like a sticking throttle, so I've never wasted a thought on twin cable throttles.

Swapping them for the 36mm Dellortos brought on a gain in low- and mid-range only.  Top speed, and probably max hp as well, stayed just about the same, which has been enough to breeze past all but the single quickest 180? triple (Robjota), and quite a few 120s as well, at Spa the past few years!

Mingh,

As for period correct carb, there's not much getting around the venerable PHB/PHF.  These superceded the Dellorto SSI for sport applications.  The SSI was a true smooth-bore, much the same as the Amal GP, which is slightly more efficient in terms of flow.  Unfortunately, both have no provision for an idle circuit, so not much good in traffic...  Then there's the Lectron, also used mainly in sporting applications, not sure if they have an idle circuit, also quite rare.  Apart from these, there weren't many large-bore carbs on the market at the time.  Amal Concentric larger than 32mm were restricted to mainly spanish 2-strokes, with a brief spell on SFCs, Bing were just beginning to emerge on the scene with carbs larger than 26mm with their 54 and 74 series, supplied mainly to Maico, etc.  BMW relied on Stromberg licensed CV Bings of up to 40mm.

I'm still kicking myself for letting a set of 3 35mm SSIs slip from my grasp many years ago... would have been perfect for a racing triple!

piet
 
Keihin CR?
figB.jpg
 
The CR's are a brilliant carb and easily tunable too. The only reservation I have is using them on angled installations.
They have the pilot/slow run circuits on the engine side of the needle jet same as round slide Mikunis - and early amal GP's.
What this can mean is a permanent dribble of fuel through those circuits....
Dellortos of course have the slow circuits on the air intake - or uphill - side so are able to mount at severe downdraft angles.

Surprising how many RS users don't realise there are alternative anchor points for the return springs...disable one totally and set the other on the softest setting.
 
Lothar,

Don't think Keihin CRs were readily available in sizes larger than 28-30mm at the time, as they were pure race carbs catering mainly for 2-valve 4-stroke multis, which didn't need much more than 30mm back then.

So not really "period".

piet
 
Laverdalothar said:
BTW: I can't proof it with a dyno print-out, but from the "butt-o-meter" if you will, the installation of the home-made power-blades have done something good on low end throttle response, too...  ;) But that may be just me arguing myself the invested time... not sure ??? For sure they haven't done anything bad, that's why I keep them...  ;)
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Lother,

All the "power blades" do is halve the effective carb cross-section, allowing your huge carb to behave like a much smaller one up to 1/2 throttle openings... this simple "improvement" effectively shows up the deficiencies of a too large carb!

piet :-*
 
sfcpiet said:
Lothar,

Don't think Keihin CRs were readily available in sizes larger than 28-30mm at the time, as they were pure race carbs catering mainly for 2-valve 4-stroke multis, which didn't need much more than 30mm back then.

So not really "period".

piet
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Well, yeah, sometimes size matters...  :D

However, many use them on period race bikes with those larger sizes. Not sure the rules exclude them... ???

To the point of the angle: true, but what about using them with angled studs? Like the ones from Red f.e.?

To the point of to large FCR carbs: the 84 Nm at backwheel around 3000 rpm were measured without them. How much to large can they be then?

Wonder why so many KTM's use them when using FCR's. Are they taking all to big carbs, recommended by their top tuners? Mmmhhh...  ;)
 
Laverdalothar said:
Wonder why so many KTM's use them when using FCR's. Are they taking all to big carbs, recommended by their top tuners? Mmmhhh...  ;)
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Not only does displacement need to be considered, but also inlet port cross-section, cross-sectional area of valves at full lift, valve duration, piston crown area, etc, etc.

You will find todays big singles have about twice the valve/port cross-section mated to about twice the displacement of a single cylinder of a Lav triple, as well as far superior cam designs... they breathe far more efficiently and need the greater carb cross-section for max performance.  But, nevertheless, they also suffer from over-carburation at low revs when gas flow isn't yet in its stride!  Exactly the same as you're experiencing. :D

Decrease the stroke, increase the bore by 30% and fit a 4-valve head on a triple... that's when a really big carb becomes a necessity.

Mingh inquired about the best period carbs, not what's available today.  Carb sizes are not limited under most european classic regulations, the use of flatslides however is usually forbidden and the 35CR Keihin is the carb of choice for the multis.  Most of the big twins run 40 or 41mm Dellortos, and still manage to whip most of the triples and fours, go figure... :D

piet
 
Hi Piet,

I did not say I had a problem with the carbs, they picked up the revs even from low end better than the Dell'Ortos ever did. However a good situation was even improved with these power blades (at least I think that's the case, as said I do not have anything to prove that).

BTW: the 750's have the same displacement per cylinder, have the same inlet diameter, have the same valve sizes (I think) and use 36mm Dell'Orto as a standard. I think all tuners except Laverda themselves used 40mm... like Cico and Sulzbacher, right? But on a ported head (just as mine is).

I had 40mm Dell'Ortos on my bike (which SteveB. now has...) and I never got them running good nor did Dynotec. They were not bad, but no where near the Keihins in low-end and midrange. Top-power with them was 91HP max (clutch), but to be fair, this was more due to a wrong designed collector. after cutting that out and get it replaced by 2 single pipes, it ran more freely but still not as good as with the Keihins. When I brought the bike to Detlef (DHL-Superbike), he measured 90HP at the backwheel, which isn't that bad (roughly 98HP clutch), however, with the Keihins he went to 100HP at backwheel and 100Nm with a very nice and flat torque curve. Not sure smaller carbs would really improve that...  :-*

I talked to Topham btw. who I think we both agree on knows his carb-stuff well. He said to me: bigger carbs are one option to gain more top-end power. From a certain point on, you don't get more power, but it also does not drop if you go higher. The only thing you have with bigger carbs is that low end gets more tricky to set up and the carbs get more sensible to low-end settings. Guess what he recommends for the 750 Ducatis? Right - 40mm carbs...

I made deep analyzes of what people use on roughly similar engine concepts and found that the only ones that always stay with smaller carbs are the Laverda people. I was told that 40mm carbs will never work on my engine. Surprise, surprise, they do... On the 1000 SFC with absolutely standard engine, low-end is now similar to the 180? triples (which never was the case with any of the Dell'Orto's I tested, be it 32mm or 36mm...). And the Keihins on that bike are 39mm - bigger than anyone would ever recommend for a 1000ccm Corsa engine, right?  ;) 105HP documented and up to 110HP in total (clutch) with a more open exhaust speak a word...

For the new project though, I will go smaller, as the head will be a modified 32mm one and displacement will be "just" 1078ccm. We chatted already about the engine, right...  ;)

Still - besides the size of the carb, I think we all agree that the dell'Ortos were the best available choice at their time, so for classic racing where round sliders are mandatory, I think its still good to go with them. Especially as low-end and midrange do count less on a race-track than top power (except for very small tracks). For my bikes I will stick to flat sliders (be it Keihin or Mikuni), as my riding is mostly on roads and that is where low and midrange deliver most fun...  ;). Easy to go back to Dell'Ortos, as I have all parts laying on the shelf...  :D
 
Hi Chaps,

Could anyone advise what bikes the Mikuni TMRs were fitted to?  Are they 32 or 36 mm and which would best suit a 120? Are they often available secondhand?

Regards, Andy
 
Andy, I believe they were just an aftermarket accessory, like the RS series. They were available in 35, 36, 38, 40 and 41 mm sizes (that I've been able to find), VERY expensive, at least 3x the price of RS carbs. There's even a Japanese home market model with a red cap (normally silver alloy) that has the hollow needle seal into the emulsion tube and a line of tiny holes in the back of the needle spray fuel evenly through the throat. Used very rare, although if you read Japanese they apparently do appear on Japanese auction sites (I saw a mention of a Japanese Yahoo auction, but haven't been able to find any yet).
But they do look trick as hell, and seem to fit a lot better than the RS36s. I'd much rather use my standard airbox but getting the rubbers to fit is just too much trouble, especially considering what new ones cost if you split the old ones.

If you have the Google Chrome browser installed, go to http://www.yoshimura-jp.com/products/engine/carb/tmr.html. Chrome translates for you (sorta, if you ask nicely, although it doesn't work too well with Japanese). There is an English translation of the site available from a tab, but you can't see any prices unless you're looking at the Japanese version of the site.

And today's price for a set of 4 36mm TMRs is 185,850.00 JPY = 2,388.20 USD (1,827.54 EUR, 1,524.34 GBP, 2,352.19 AUD), if you're in Japan. Tax plus shipping will also have to be added. Make the RSs look positively plebian in contrast :D :D.

Ken
 
I think Topham offers the TMR 36 as a set somewhere around 1.300?, which is way better than the japs price but still 1,5 x what the RS cost. He has built several for German and other European customers, however is not showing the current price on his webpage...
 
But they do look trick as hell, and seem to fit a lot better than the RS36s. I'd much rather use my standard airbox but getting the rubbers to fit is just too much trouble, especially considering what new ones cost if you split the old ones.
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What's the problem?  Just warm them up a bit...

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Reggie, when I installed RS36s with straight rubbers like you show for your 3c, the petrol tank rubbed on the tops of the carbs. I tried raising the back of the tank up but didn't like the look. I ended up using a set of Wolfgang's curved snowmobile rubbers, but had the carbs fall off a couple of times. So now I have a bracket holding up the back of the carbs.
I tried heating up the airbox rubber a bit as you mentioned at the time when somebody else commented, but I think you must have had a stretchier rubber than mine was made of, even if I could have forced the issue they would have split.
Then one of the snowmobile rubbers split open, so now I keep a spare set and carry a spare rubber.

Ken
 
Laverdalothar said:
I think Topham offers the TMR 36 as a set somewhere around 1.300?, which is way better than the japs price but still 1,5 x what the RS cost. He has built several for German and other European customers, however is not showing the current price on his webpage...
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Lothar, Yoshimura's price is for a set of 4, and they are the super-trick Japanese-market only ones. But still twice as expensive as Topham's. I'm still trying to find this mythical Japanese auction site where used ones supposedly appear.

There's a set for a CBX on eBay Deutschland right now. Would nearly do 2 triples. Pity they're only 32mm.

Ken
 
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