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Anyone using Mikuni 38's????

Supaflee

Cruisin' Guzzisti
Joined
Apr 17, 2012
Messages
201
Location
Tauranga, New Zealand
If you are using a Pair of Mikuni TM-38's and have them on your Vee 1000 , please share with me the jetting that you have found most satisfactory for general all round riding .My engine is otherwise pretty stock (I think).
Mine Carburettors have been messed with hugely , one float level lever was installed upsidedown (extremely lean) and would only run on the idle air needle at low throttle openings , up to 3000 rpm. The other , the float level was 22mm and not 17-19 as suggested as standard by Mikuni (Sudco).
She's going like a rocket , now that I`ve got things the "same", in each carb , but I just need to know how far away from optimum I am with my Carbs and Jetting , so if you can help me please do so.
Regards Supaflee
 
hi, a friend of mine has been using mikuni tm 38 on his le mans 1000 for the last 20 years ,we would ride at about 80-100 mph most of the time and his carb specs are 180 mains,40 low speed,100 air bleed,needles j8-6fj41 ,slides 3,0 stamp on them,e-ring vm20/369,open reverse cone mufflers,k-n air filters.cheers.
 
That's interesting! I envision using Mikuni TM 34 on a small valve round fin engine. I know a couple of other guys intersted in the conversion to Mikunis, too.

mkiv16 : do you mean 180 main jets using Mikuni references for 4/042 jets (that would be 122.5)
tablemikunifryq2.jpg


or the usual 1/100-th millimeters (that would be jet 4/042-450 ) ?

It also seems that throttle valve 3 is not the standard, and this is not cheap. I look forward to reading about any reason why you used it instead of the stock (4) one?

Supaflee: I did not read just the best about sudco. Data for stock Mikunis is really easy to find. 18 mm is the stock height for TM34 - for comparison - it is 24 mm for the stock Dellortos, and only 14 mm for the TM33 pumper carb.

You should find any data for your carbs from here http://www.mikuni-topham.de/ENGLISHSITE ... glish.html or there http://www.mikunioz.com/tm_series.htm be it a VM or any TM_ one.

It (Actually TMX carbs)

mauros533.jpg


seems to work on the track too (thought the powerjet was a 2-stroke only feature, though.)
 
Thanks for your input with my enquiry.
mkiv16 , you are just down the road from me here in Tauranga. I used to enjoy riding at the speeds you suggest , but I got pinged too many times and almost lost my licence when I had my TL 1000.I bought a real good detector and havnt had a ticket since , best money I ever spent .
Ive still got the detector but not the TL 1000 , so after a few in-between bikes bought this 1985 SP11.Someone has done an awsome job of making it a rocket, I just love the damn thing .
As soon as I get the charging problem sorted on my Guzzi , I'd like to come for a blast to taupo and meet you somewhere there for a coffee and a yak?? How about that, or meet you in Rotorua at the lakeside cafe , or at Okororiore pub??
Dont get me wrong , There's nothing wrong with the way my bike is running , it goes like hell, and I like it . I was just curious to know if many people had made the change to Mikuni's and what their jetting is .
My carbs are Standard Mikuni TM38-85's, with the only change being the mainjet size . Down from 230 to 200 and the needle is in the lowest slot.There is a Hypercharger on each carb, Im not sure if I really like them , of if I'll go to pod filters yet. They were there when I bought the bike , so I'm leaving them for a while anyway.
Chopsauce , thanks for your input . Your bike looks very cool to me. Yes , the TX carb is for two strokes , but is ok on a four stroke I understand as well.
When I get all my other little problems out of the way I'll post some pics for you .
Cheerz........Supaflee
 
Didn't I asked to be notified when a reply is posted?

Supaflee : you're welcome, but the pictured Guzzi is that of a spanish racer - I guess, not mine. I am compiling some data about Mikuni TM. TM 34 especially. I'll post the table soon.

Your setup seems very different from what I could read. It looks like Yamaha Blaster owners found the stock Mikunis too lean (too rich on idle, too) and put bigger main jets - close to 380 on a TM 34. For comparison, the Mikunis from Yamaha 125cc YZ have a 270 main jet.

Your pilot jet seems consistent with foreign data, but your 200 main jet actually corresponds to a 130 for Dellortos, which seems very few. As a comparison, the VHB30 from the V7Sport comes with a 140, or close to.

Just guessing what a starting point would be to setup the Mikunis for a stock V7Sport (750S3)...
 
Mikuni TM setup

ChopSauce said:
I am compiling some data about Mikuni TM. TM 34 especially. I'll post the table soon.

Here it is :

tmsetup2.png


_

Notes:

[1] La guzzithèque ...
[2] Flow rate (diam. [mm/100])
[3] Poor rationales for - http://www.cafe-racer.info/phpBB2/viewt ... f=4&t=3170 -
Code:
new_main_jet_size = old_main_jet_size x ( new_carb_size / old_carb_size )^2 - 2%
[4] Std: 230(137.5)
[5] Std: 22.5
[6] Tables below
[7] Last digit (after "-") is clip position
[8] Original Yamaha equipment
[9] Fixed

-

Tables:

needlejet.jpg
needlejetsizes.jpg


ChopSauce said:
Just guessing what a starting point would be to setup the Mikunis for a stock V7Sport (750S3)...

Any comments - especially about the main et pilot jet sizes?
 
MMMMmmm, you've got me going a bit now , regarding the mainjet size being 130.
My experience tells me its too small for a 500cc cylinder and should be somewhere around 230 240.
Im going to run a few trials.
If I need to , I'll ream the jets , I've still got my original set of drills and swages here somewhere , no way is this engine going to run lean up the top end !!
Regards Supaflee
 
Hello.

For me this is a very interesting topic. In a near future I am thinking to put a stock Lemans engine to my 850T (I am thinking to overhaul its engine and meanwhile I will put the Lemans one I bought time ago...) . I don't have carbs for this engine, so I will buy new ones. I think Dell'ortos are good carburettors but I have other bikes with Mikunis and I like them!

If anyone has got data about Mikunis for this engine it will be welcome... also I have doubts about the size of the carbs, 34 or 38 ?? I would like to have a good running bike, pulling from the bottom band...
 
I saw an excell spreadsheet for choosing carb. sizes on this forum. I also posted a few preliminary data on the subject here: http://www.forumguzzi.fr/viewtopic.php?f=21&t=530 - in french, sorry!

I'll manage to translate the captions in english, as well, but it appears that 38 seems the good choice for upgrading a LeMans with stock 36 mm diam. carbs, for which the 40 seem "over-optimal". For a 850T/T3, 36 carbs seem to be the way to go, but this seems to require some porting(not sure this last one is the correct term.)

I am choosing 34 mm diam. carbs because my bike is a 750 (S3) and I do not want to modify heads at all (stock inlet duct diam. is 34.5 approx.)

Supaflee: I am looking forward to reading about your experiments -

... otherwise I cannot understand why a bigger carb would alter low end performance ? (Just curious)
 
Thanks chopsauce . Experiment ,,,, what experiment?
Im not quite with you there .
The carb size page you included is surely great for those academics that like plenty of calculations. Me, well no , I dont do calcs too often, Im more of a applied logic sort of critter .
I use an old book called "Speed And How to Obtain It" .It's an early Clymer Publication.From memory I got it in 1967 or 8 .Have a snoop around , it maybe available online somewhere.
Best regards Supaflee.
ps havnt tested my mains yet for high end fueling , info later on that.
 
You're welcome!

Supaflee said:
Thanks chopsauce . Experiment ,,,, what experiment? [...]
ps havnt tested my mains yet for high end fueling , info later on that.
You got it!

Note: I posted the link to my tables for bkt rather. This is not something of a detailled study, rather a summary of the reasons why I'm going to 34 mm carbs and how they compare with common setups. The tables where primarily intended to fight the beliefs of a few ones arguing against 30++ mm carbs on small valve engines.
 
Not yet. The original post is too long and it requires more than just a translation. As soon as I have written an english version, I'll post it on the forum.
 
Physically, it depends even on the year of your carbs. You can find the dimensions of the recent ones on the internet, for example here : http://www.mikuni-topham.de/index.html

Due to the original 3 bolts pattern of the Guzzi heads, it is probably better to use a straight plastic connector on a Guzzi manifold, or a custom one. You will also have to deal with the cables, and filters - or velocity stacks - plus ...
 
Thanks for that link chopsauce . Its very handy to have the info , especially in English .Im sure it will also be helpful to GuzziDon for his plan . Your advice for him is good although my Mikuni's fit straight into a rubber , 3 bolt manifold .
Regards Supaflee
 
There seem to be only 1 diameter difference between Dellorto and some Mikunis so maybe the adaptors for bigger Dellortos work. The custom manifold is THE solution, however, because you can be sure the inner diameter of the intake remains constant(*). There - http://www.motocarb.co.uk/inlet%20connectors.htm - seem to be any connector you may require.

(*) be warned some Mikunis for 2 stroke OEM application have not a constant diameter, and that should not improve performance.
 
I have asked about this to a mikuni dealer and they advise me to use the TM36-31 carbs. They have the base settings and I will have to do the fine tuning.
What do you think about this option for a Lemans stock engine?
 
Back from holidays. Sorry for the delay: Indeed that would be worth having the support from a Mikuni reseller, at least to be sure it mounts.

The TM36-31 is a 4 stroke "pumper" carb, so this seems close to ideal (even for a small valve engine - especially with a "sporty" camshaft, does it seem). For a big valve engine, the 38 could be a fine upgrade, but whatever the solution any upgrade requires porting. I thought not but my heads have already been tuned, hence my mistake.

I'll have to write an english version of my post about carb sizes soon. Send me an e-mail as well.

Note1: I found a carbsize.xls file on this forum, somewhere :?

Note2: I remain insterested in collecting informations about Mikuni settings. The updated table is here : http://www.caferacerclub.org/t20810p45-v7sport-76 (the 2 last lines - currently (2012/08/24) - from this thread)
 
Here is the spreadsheet again if you can't find it in the other thread. Enter the bore, stroke and carb size into the spreadsheet. The calculated RPM +/- 1000 will be the optimum efficiency.
 

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