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34 mm or 36 mm carbs?
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bvis
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PostPosted: December 28, 2009, 10:07 pm    Post subject: 34 mm or 36 mm carbs?

What is the best setup to go with, 34mm carbs or 36mm on a stock engine. My carbs are shot and i need new ones im just not sure which ones to get.
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yamaman
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PostPosted: December 28, 2009, 10:58 pm    Post subject: Re: 34 mm or 36 mm carbs?

34's, what's wrong with what you've got? Some say shot, but can be made good!
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yamaman
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PostPosted: December 29, 2009, 7:57 am    Post subject: Re: 34 mm or 36 mm carbs?

Please make sure they are set up for an XS before you buy, 650central is the best source if your buying new. Snowmobile carbs etc are miles out in their settings/components!
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bvis
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PostPosted: December 29, 2009, 6:03 pm    Post subject: Re: 34 mm or 36 mm carbs?

well first of all ill have you know im a big fan of working with what i have and im not like all these other "bike builders" who buys a hardtail and has someone else weld it on. i made my hardtail my self. and back to the carb issue, when i bought the bike i opened up the carbs and there was obout half a dozen dead bumble bees in there and it was neglected and left outside for years and everything about the carbs are just totally shot and crusty. so i just wanted to know which setup is better 34mm or 36mm.
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yamaman
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PostPosted: December 29, 2009, 6:16 pm    Post subject: Re: 34 mm or 36 mm carbs?

Ok, no problem...........Like I said 34's are my choice. Some have run 36's though slightly harder to get right & probably at the expense of some bottom end. 1000's of 650's on 34's. There's some good info in the vault section on VM's, gives some good baseline settings, if your interested. Cheers
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royfisk
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PostPosted: December 29, 2009, 6:30 pm    Post subject: Re: 34 mm or 36 mm carbs?

bvis;
I assume your talking about mikuni vm carburators. The choice isnt hard first ask yourself how this bike will be riden. If your a go fast guy and are in the above 5000 rpm range then the 36mm carbs will be a better choice. If you are normal and ride legal street and want better fuel economy then the 34's will be a better choice. Either way tuning of either set is almost identical, with all internal components. As for looseing bottom ends with 36's thats BS. Carbs dont cause that riders do. Besides who's kidding who here yamaha put 38's on for 8 years before they sized down. The only advantage of 36's dont happen till your in the upper rpm range. I run 34's on stock motors and 36's on modified motors. 34's will also build better low end tork. Hope this clears things up a little for you.

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royfisk
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PostPosted: December 29, 2009, 6:53 pm    Post subject: Re: 34 mm or 36 mm carbs?

yamaman I appologise I read your reply wrong, You are absolutely correct with bottom end tork. I thought you were saying that you might loose your bottom end from running 36's. As for tunning though both sets are almost identical in all internal components and jets sizes. I want to try a set of 38's on a 750.
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yamaman
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PostPosted: December 30, 2009, 2:16 am    Post subject: Re: 34 mm or 36 mm carbs?

No problem Roy, was just trying to point out that all VM 34's (or 36's) are not created equal. You can buy cheap carbs, then find you don't have a enrichener circuit. Also with wrong slide, needle jets & jet needles....More than just pilot & main jets. Though maybe just wasting my breath......Bvis obviously knows everything he needs to know, just not what size he wants??????
Original question was "on a stock engine".

Of course you need to take intakes & airfilter in to consideration, cables too........Plumbing & vacuum lines/take offs.......Always more than just a simple swap.

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yamaman
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PostPosted: December 30, 2009, 9:37 am    Post subject: Re: 34 mm or 36 mm carbs?

Roy, I don't know, but I'd guess that for a given size, a VM would flow more air than a BS, mostly due to the butterfly. Also the slide both in reaction, and vacuum modulation.

Like I say, I'm only guessing here, but a VM 34 would perhaps be compareable to a BS38 in actual CFM on the road??????

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