[Mr. Mojo]

Hello all!
I have a set of Mikuni vm30mm carbs ordered, they should be coming in within the next two weeks.
I'm not sure what they will be jetted with upon their arrival, whatever mikuni ships them out with. I am sure they will be way overjetted for my application -a stock 350 motor, the only other modifications being mac 2-into-2 exhaust.
So, does anyone have any idea what jetting would be ideal for my purposes?
I have posted this question in other forums without much success, I am aware that it will be a trial and error proccess but what are the two or three main jet sizes I should start with? Pilot?
I will post up the end result, hopefully it can serve as a guide to those looking to do this mod in the future.
Thanks, Trevor

 

[66Sprint]

Trevor, Your FIRST problem is most who use Mikunis use either 32 or 34mm bores..... So the jetting we use won't help you much......

 

[fasterspider]

I would put the same size jets into the Mikuni carbs that were in the old KeiHin carbs to start with and see what happens.

 

[Bird76Mojo]

Luckily (for you) it's been done before, and should be well documented on the net somewhere. BUT like Steve said most do use 32-34mm Mikuni's. Probably 32mm most often I'd assume. There are several nice sites on the net (I can't remember where, sorry) where people have built really nice race bikes from CB350's and switched to Mikuni carbs. There was one that a couple schools built two stunning examples, and they may some info available there? Keep in mind that your elevation will make a big difference in the proper settings and jets. Sorry I can't help more. Buff Harsh would know..

Here's some reading for you though:

VM30's - http://forums.sohc4.net/index.php?topic=52521.msg563097

http://www.caferacer.net/forums/topic.a ... C_ID=10651

http://www.caferacer.net/forums/topic.asp?TOPIC_ID=6799

http://www.motorcycleshopper.com/articl ... reword.htm

http://www.vjmog.com/modules.php?name=F ... pic&t=2836

GB :mrgreen:

 

[Mr. Mojo]

Yeah I've posted the question on caferacer.net and also ohio cafe racers but no definite answers. I opted for the 30's instead of 32's after reading up on the subject. Seems that the 32's are really hard to dial in on a stock motor. I know there are a couple of Ebay outfits selling the 32's in a kit for cb350 owners but I recommend that anyone considering upgrading take into account what mods they plan on doing (or don't plan on doing, as the case may be). While 32's are ideal for track bikes (with oversized pistons, Megacycle cams and the lot and going WOT 90% of the time) they are basically overkill for a stock engine and will rob you of low end throttle response. My bike will be a daily rider and spending as much time in city traffic as highway so I want nice, even acceleration from the redlight. Now, take all of this with a grain of salt as I am most certainly a noob, but I have done hours and hours of reading and talking to folks and that's what I've come up with. I'd love to hear from anyone running either the 30's or 32's, tell me your experience.

 

[Bird76Mojo]

If there's anyone here that has used VM30's on a CB350 I haven't heard of it. That doesn't mean there isn't though. That link to the SOHC looked promising, although I didn't read all of the way through it to be honest.

If there's one person I could recommend on this subject it would be CrazyPJ. He seems to really know his carbs. Additionally, you might try to contact one of the vintage race teams that run 350's and see what they tell you. They might offer to set them up for you for a nominal fee. Todd Henning racing offered to set mine up for the 450 for a fee, but I never asked for the exact amount.

GB :mrgreen:

 

[Mr. Mojo]

Yeah that SOHC link does look promising, I'll be following that. Maybe I'll just join that forum as well so that I can email the guy who posted that and ask him what finally worked! There's just so much voodoo involved in jetting. It's basically that and wiring standing between me and a running bike.
By the way, I have two options available to me for air filtration: a set of pods and a pair of screened velocity stacks. I want to run the stacks. Again, they are screened not open, but am I inviting more problems than the performance gains are worth? And also how will this affect tuning characteristics? Thanks!

 

[66Sprint]

Stacks are great for a high-revving racing bike that will be fully wound-up most of the time, and there are jetting "adjustments" to make for the increased airflow volume....Remember, the "racer" will be getting torn-down and internally checked way more than yours will as a street bike....
Pods are much more suitable for a streetable bike.......JMHO.... Steve

 

[Mr. Mojo]

So an annual wintertime teardown probably wouldn't be sufficient on a street bike running stacks?

 

[66Sprint]

Everyone I know that is running open stacks tears down after nearly every race weekend...... In a few running hours, pistons, rings, valve seats, etc, can get scuffed by the airborne grit that gets through the screens...Some of that grit ends up in the oil....You go from there....

The early Sprints came from the factory with bare stacks... Air cleaners were quickly added... (sometimes a "sock" OVER the stack)......Except for hard-core WFO racing, the nominal improved flow of a "stack" is exceeded by its disadvantages.....JMHO

I know, I know....They look cool.......but still running is better!

 

[Mr. Mojo]

Yeah they do look cool. So when I saw a pair on Ebay that fit the carbs that I planned on getting, I jumped at the chance and won the bid. I kinda knew they weren't practical but like a lot of things on this build I've tried to find a balance between form and function. I guess the good news is A) I didn't pay much for them and B) if I do ever decide to race my bike I already have them.