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mikeoxbig

Mikuni VM 26 mm carburettor - montesa 349

16 posts in this topic

hi,

I have a 1982 Ulf Karlson montesa cota 349 does anyone know what the correct jet sizes are for the Mikuni VM 26 mm carburettor for this bike. I've tried bultaco  inmotion and they're clueless ! they just wanted to sell one of their extortionately expensive carbs for a 349.  inmotion want £177.00 + p&p for a mikuni carb to fit a 349 but there's a seller on ebay selling what looks like an identical one (new) for £98.00 inc p+p I 've got the jet sizes for that, I just need to know if they are the same as "inmotion" carb.

cheers.

Edited by mikeoxbig
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Don't want these Ads? Why not sign up as a Trials Central Supporter.

If In Motion are so clueless buy one elsewhere...  They stock very hard to get Montesa parts and a top service.  Don't slate off at one of the best twin shock parts suppliers in the UK.....

 

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Always found Inmotion excellent, but if you wish to go elsewhere then I think Mikuni UK are good to deal with.

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I'll think you'll find any of the suppliers for non standard carbs would be reluctant to give out their hard earned jetting specs. Another reason might be the fact that a 26mm would be considered by most as being too small for a Cota 349 and they simply have not ever jetted one for this model. A 28mm would be a better option in my opinion but I'm of no help with jetting specs. As a general rule of thumb, 26mm are best suited for 250cc and 28mm for 350cc on a Trials bike.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Speak to your ebay seller, I'm sure they will have all the information you need. 

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1 hour ago, gasserguy said:

If In Motion are so clueless buy one elsewhere...  They stock very hard to get Montesa parts and a top service.  Don't slate off at one of the best twin shock parts suppliers in the UK.....

 

that's just your opinion. " I am " buying  one elsewhere...that's the point !  I found their service awful ! waited 3 weeks for a rear mudguard,  when I contacted them, they hadn't even processed my order ( blamed  new staff) when it did arrive I had to trim off all the bits from the cast on it. next order, they missed items off my order ( blamed  new staff) they don't answer emails. I only use them as a last resort.

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Likewise In Motion have never let me down. They are relatively new to Montesa though.

I bought my own 'ebay' mikuni from a specialist who gave me all the jet sizes etc but the fuel pipe inlet was on the wrong side and the problems that caused would be worth £100 not to have had!

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Mike - unless you enjoy tinkering rather than riding, you're better off sticking with the standard Amal Concentric MK2. In my experience, Mikuni's are a pain in the ar$e to jet for non-standard applications due to the number of different jet options. Even if you haven't got an Amal on the bike, you'll probably spend more on jets trying to get the Mikuni to run correctly (because you've got no base settings for it) than you would on a brand new Amal. The correct jet sizes are widely available for the Amal on the 349 also.

 

And just to add my two penneth worth regarding InMotion - they've always given me excellent service (and shown a lot of patience in dealing with my ridiculous questions)

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On 18/03/2017 at 10:09 AM, b40rt said:

Speak to your ebay seller, I'm sure they will have all the information you need. 

Funny how they never answer a question that doesn't suit their agenda. Looking forward to @mikeoxbig posting his carb settings when he has spent a fortune in time and jets, for the benefit of the trials community.

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3 hours ago, b40rt said:

Funny how they never answer a question that doesn't suit their agenda. Looking forward to @mikeoxbig posting his carb settings when he has spent a fortune in time and jets, for the benefit of the trials community.

yeah, jets are very expensive ! I need at least 3 lmao  how do you spend a fortune in time ?

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Mike - without wishing to patronise you (well OK, maybe just a little bit) I think you'll find that time can cost a fortune due to a concept known as "opportunity cost". This is the concept whereby the value of time is measured by what else you could have been doing with the time instead of the task you chose to do.

So for example (hypothetically speaking of course) if a person had no friends, no social life and nothing of greater value in their life than getting an unsuitable carburettor to run on a bike that it was never intended for, then the opportunity cost would be low. If however such a person had a life and actually enjoyed riding their bike and having a laugh with their friends whilst doing so, then their time might be better spent doing that instead so the opportunity cost would be higher....

And as for your belief that you'll only need 3 jets to get it running I assume you mean pilot jet, needle jet and main jet? But what about Throttle slide cutaway? What about needle taper? What about emulsion tube size? Float height? 

That's four more variables that I've just thought of from my own experience of Mikuni's and I'm sure there'll be more that I don't even know about.

So what's the probability of you getting all 7 of those variables correct first time with no base settings?? 

And that's before you consider the fact that (as you've previously been told by Fourex) the carb is too small for the engine anyway.....

If you're still keen then you might wanna try Allens Performance in Nottingham (UK) - they're a Mikuni specialist

 

Good luck with that one.....

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4 hours ago, montesamadness said:

Mike - without wishing to patronise you (well OK, maybe just a little bit) I think you'll find that time can cost a fortune due to a concept known as "opportunity cost". This is the concept whereby the value of time is measured by what else you could have been doing with the time instead of the task you chose to do.

So for example (hypothetically speaking of course) if a person had no friends, no social life and nothing of greater value in their life than getting an unsuitable carburettor to run on a bike that it was never intended for, then the opportunity cost would be low. If however such a person had a life and actually enjoyed riding their bike and having a laugh with their friends whilst doing so, then their time might be better spent doing that instead so the opportunity cost would be higher....

And as for your belief that you'll only need 3 jets to get it running I assume you mean pilot jet, needle jet and main jet? But what about Throttle slide cutaway? What about needle taper? What about emulsion tube size? Float height? 

That's four more variables that I've just thought of from my own experience of Mikuni's and I'm sure there'll be more that I don't even know about.

So what's the probability of you getting all 7 of those variables correct first time with no base settings?? 

And that's before you consider the fact that (as you've previously been told by Fourex) the carb is too small for the engine anyway.....

If you're still keen then you might wanna try Allens Performance in Nottingham (UK) - they're a Mikuni specialist

 

Good luck with that one.....

yes, you're right... I must have no friends and no social life because I want to change my carb ? you come across as a right merchant banker.(float height) ffs !

(Inmotion)  have a 26 mm carb jetted for a 349 £177.50 but hey, that's impossible...they can't have,  its far too small ! but your comment was a good example of someone with a dull life and nothing else better to do  than sitting on their computer replying to comments. 10418161_473336969488455_5107453577451255416_n.jpg

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A smaller carb will "improve" bottom end performance, just what a 349 doesn't need.

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The pre-jetted OKO 26mm I bought for my Cota 348 from a trials specialist supplier worked perfectly straight out of the box and was reasonably priced.

I'm not sure if I can name the supplier on the forum so I didn't

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