Mikuni carbs

danno · Full Member Joined: Mar 04, 2006 Posts: 212

Good,bad,or more more trouble than they are worth? I am considering this mod,and feedback would be most appreciated.

oldskoolcool · Full Member Joined: Sep 08, 2007 Posts: 372

uuuh, they are stock with mikuni's....

xsleo · Posted: April 4, 2009, 12:03 am Post subject: Re: Mikuni carbs

Well from what I have read , the Mikuni round slides can be a pita to get tuned right. The stock carbs can be too. You have the stockers and getting jets and such to tune them are cheaper than the Mikuni's. The Mikuni's can give you more top end power, but can have poor throttle responce.

danno · Full Member Joined: Mar 04, 2006 Posts: 212

I should have specified...I incorrectly assumed that people would know that I was referring to the roundslide carbs.

oldskoolcool · Full Member Joined: Sep 08, 2007 Posts: 372

bs34 or bs38's on yours stock?

danno · Full Member Joined: Mar 04, 2006 Posts: 212

yamaman · Posted: April 4, 2009, 5:24 am Post subject: Re: Mikuni carbs

Mate, plenty of posts around with info on VM's. Not at all difficult to tune, all the baseline settings are around and reasonably similar.
They can be difficult to sort if they are set up for a snowmobile or a cessna
but thats the nature of them, they can be tailored for many applications!

So you can either buy from 650central, apparantly they come pretty much sorted from there! Or if you want secondhand or other sellers gear, take a chance. If you get a worse case set, you might need to replace the slides, main jets, pilot jets, needle jets, jet needles. In other words everything!
So be careful what you buy!

Poor throttle response - only if set up poorly! No lag like CV's, direct, precise carburation!
VM jets are dear? Are they? How much? Whats a diaphram worth?

Lots of people swear by Johns needles for the 34's.
Lots of people swear by VM's
Others love the power jet Dellorto's
Could always be different and put TM's on or a Keihin, something with a power jet!

y TRX 850 has got BS38's, I might trial them on the XS some day (& vice versa, put the VM's on the TRX)
Up to you in the end, it's only got to make you happy, cheers

weekendrider · Posted: April 4, 2009, 9:02 am Post subject: Re: Mikuni carbs

yamaman wrote:

If you get a worse case set, you might need to replace the slides, main jets, pilot jets, needle jets, jet needles. In other words everything!
So be careful what you buy!

Thanks yamaman I've looked at the cost of carbs from banshee's, snowmobil's etc on ebay. Some go pretty cheap. Now I know why it might not be cheap in the long run.

yamaman · Posted: April 4, 2009, 10:57 am Post subject: Re: Mikuni carbs

Do banshees have 34's, I thought they were 32's?

ikuni make half a dozen slides, over 20 jet needles for the 34's and at least 25 needle jets!
Plus 100's of main jet sizes! Theres 3 or 4 different return springs also!

The key is being in the ball park with the slides, needle jet & jet needle, as they will cost.

www.motorcyclecarbs.co..._C1420.cfm

xs1961 · Posted: April 5, 2009, 6:22 pm Post subject: Re: Mikuni carbs

I started using VM roundslides in the early eighties as I was fed-up with the (tuning)limitations of the stock CV's.. (carbs being one of the first things you should invest in in my opinion).. Last year finding myself finacially embarrassed I sold my 34mm VM's (for more than I paid for them) & to justify this I convinced myself that installing a pair of 38mm CV's was probably the 'right-and-proper' thing to do - no need for fancy after-market carbies- CV's will give me more MPG etc... What a f****g mistake !
Last year I covered less miles on my bike than in any I can remember in the last 30-odd years ! Pissing about every other day trying to get CV's (I have at least 8 pairs to play with ) to run correctly at all throttle stages ..Drove me to despair Evil or Very Mad

I fitted a pair of 34mm roundslides last week & they were fully sorted within a day , so simple (& inexpensive) to work on & so responsive , the bikes back to how she was , already clocked-up half the miles this week that I covered in a whole 8 months last year !
All I need now is 2 more sets for the other bikes Rolling Eyes

Anyone want some CV's before I throw them out ? Twisted Evil

TheRepairMan · Posted: April 8, 2009, 5:10 pm Post subject: Re: Mikuni carbs

xs1961 wrote:

I started using VM roundslides in the early eighties as I was fed-up with the (tuning)limitations of the stock CV's.. (carbs being one of the first things you should invest in in my opinion).. Last year finding myself finacially embarrassed I sold my 34mm VM's (for more than I paid for them) & to justify this I convinced myself that installing a pair of 38mm CV's was probably the 'right-and-proper' thing to do - no need for fancy after-market carbies- CV's will give me more MPG etc... What a f****g mistake !
Last year I covered less miles on my bike than in any I can remember in the last 30-odd years ! Pissing about every other day trying to get CV's (I have at least 8 pairs to play with ) to run correctly at all throttle stages ..Drove me to despair Evil or Very Mad

I fitted a pair of 34mm roundslides last week & they were fully sorted within a day , so simple (& inexpensive) to work on & so responsive , the bikes back to how she was , already clocked-up half the miles this week that I covered in a whole 8 months last year !
All I need now is 2 more sets for the other bikes Rolling Eyes

Anyone want some CV's before I throw them out ? Twisted Evil

Oh, how well I remember going through that nightmare with the stock CV's on my 78. All I had done was change the exhaust and went up a notch with the needle and one size larger main jets and it would pop back through the carbs at full throttle just half way into the rev range.

I changed jets and moved the needle around a dozen times and never did get it perfect. Everybody I talked to back then said it was because the exhaust no longer had the balance tube. I don't know, but I wasn't about to spend $1,000 on the factory exhaust.

I'm still researching and learning which way to go with an exhaust system and new carbs, but I don't think I'll be using these old CV's any longer. I do have another set of earlier stock carbs also but I haven't ID'ed them yet to see if they could be of any use to anyone.

y problem is I've been learning about this bike so long I'm starting to forget things I use to know. Embarassed

-R

xsjohn · Posted: April 8, 2009, 6:05 pm Post subject: Re: Mikuni carbs

Little problem with the CV's boys............ Laughing

xsjohn

xs1961 · Posted: April 8, 2009, 6:34 pm Post subject: Re: Mikuni carbs

Yeah, sorry John, I know you like 'em ..You even convinced me last year to switch back but they just dont work for me with my non-standard pipes/ silencers/filters etc. ..The VM's are so much easier to mess about with ..CV's just hate non-standard filters & engine tuning in my experience.. If I had a stock bike I'd probably stick with the stock 38mm CV's but now theyre all going on to Ebay, sick of them just as I was 20 or 30 years ago .. Twisted Evil

TheRepairMan · Posted: April 8, 2009, 8:41 pm Post subject: Re: Mikuni carbs

xsjohn wrote:

Little problem with the CV's boys............ Laughing

xsjohn

There were days I could have thrown the set from Tennessee into North Carolina, John!

For the money new slides bring for a 78 model I think I'd be better off with something else ...but I'm not far enough into my project to conclude anything yet.

-Roger

xsjohn · Posted: April 8, 2009, 8:55 pm Post subject: Re: Mikuni carbs

Either find another set of CV's and learn them or go for the VM's....both have their problems..........wouldn't matter to me but the CV's are better suited for these bikes........just know what I know....and owning either will take some expertise..used them both for 40 years.....and can make either do the job.......but I would crap and fall back in it before I spent 4 or 5 hundred dollars for carbs.....and still have a learing curve for the new guy........

With the VM's you will not have the great balance and have to dick with it more often and there is that stupud choke that you can't get to.......oh well....

Then they may not fit to the stock air box which is the best.....and you will have to frick some pods on there and then dick with the crancase vent .......the reasons are numerous not to change the carbs...work on some thing useful..........pods are noisy and ain't worth a damn in the rain...........

xsjohn

xs1961 · Posted: April 9, 2009, 3:34 am Post subject: Re: Mikuni carbs

Expensive yes, no way would I pay full whack for VM's - I always wait for a bargain priced pair to turn up..
True I do have to balance them sometimes every couple of weeks but it takes 3-4 minutes only by simply removing the filters..
I can whip carbs off the bike singly.
I reverse the R/H choke lever so it sticks out.
No diaphragms to go hard.
BTW my RAMAIR foam pods are quiet & fully waterproof.

tintin · Full Member Joined: May 07, 2007 Posts: 96

I've got BING CV carbs on my BMW R75/6 and they seem to work just fine and are simple enough to work on etc.

That being said, for my XS650, I got a set of VM36's that had been on a racing XS650 sidecar. No idea at the moment how they're jetted or if the bike will run with them - haven't started it up yet.

y VM36's, and I think many of the snowmobile derived ones out there don't have chokes on them. Might be a bit of a challenge.

For insurance I scored a set of VM34's on eBay for $40 (for both) and they have the right slide which is actually the common setup for either the Yamaha or BMW. Just would need perhaps different jets/needle etc. They have chokes.

So one way or another my 650 will have VM's on it, and maybe the BMW as well. After having dismantled Keihin carb banks on Honda SOHC4's, these simple Mikuni VM's are a DREAM.

The fact that I can without tools, change slides, needle position etc. is amazing. Just love the simplicity of having the throttle cable link directly to the slide. No levers to wear out, simple simple simple.

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Yamaha xs650