Are vm28s too small for xs650?

[Norman1950]

Newbie question...
Got 2 carbs the other day and as a fool I didn't double check all the specs of the carbs. I think they are vm28s. Anyway to run these or should I track down some vm34 carbs?

Thank you for the help.

(Also did a full search on here and couldn't find any info on these and read the sudco manual, hence why I think I have vm28)

 

[Norman1950]

I guess I should also state that I am going to be rebuilding the top end, but leaving it pretty much stock cylinder size.

 

[XSLeo]

They might be ok at lower rpms but once you reach around 5 grand they might not have enough flow to feed the bike.
A VM 34 is used with good performance.
Leo

 

[Norman1950]

Here is a picture of the "stamp" on the side. Can't find any info on that stamp no.?
Thanks
I would like to just make sure these are the VM28.

(Also sorry for the newbie questions)

 

[XSLeo]

Lift out the slide and measure it. The numbers after the VM are the bore size of the slide. A 34 has a 34 mm slide. A 28 a 28 mm slide.
Leo

 

[Norman1950]

Ok easy enough.

Thanks for the info!

 

[Norman1950]

Ok now I am really confused....

All the dimensions I took don't match what the Mikuni chart has (I have attached a copy of what I am using)

Took it a part a little, minus the PJ and NJ...
Slide = 36mm diameter / 1.5 Cut out
Main Jet = 290
Needle = 6DH7
Engine side opening = 34mm
Outside filter diameter = 57.5

Oh so confused!

Now I really don't know what kind of Mikuni i have.

Thanks again!

 

[racerdave]

Based on your numbers you have a 30,32, or 34 mm carb.

 

[Norman1950]

Thanks for all your help.
Think I have determined that I do have VM34 carbs. Based on the measurements and help from here and this site http://www.allensperformance.co.uk/products-vm.html, I am pretty sure I have what I wanted.

From what I can tell; I have the VM34-275s

Now to the fun part of tracking down the correct jetting and such.

 

[racerdave]

What will you be running for pipe's and filters will also need to be considered for your jetting.

 

[Norman1950]

Yes, I was going to go ahead and run probably Mike's filters and then fab up an exhaust. I read all about the tuning of the VM34s. I will slowly keep an eye out for the proper slides and NJ and so on through here and other parts of the internet.

Right now I am very far from worrying about this too much, just nice to know I don't have to track down carbs now.

Thanks.

 

[lonzo22]

Yes, I was going to go ahead and run probably Mike's filters and then fab up an exhaust. I read all about the tuning of the VM34s. I will slowly keep an eye out for the proper slides and NJ and so on through here and other parts of the internet.

Right now I am very far from worrying about this too much, just nice to know I don't have to track down carbs now.

Thanks.

I installed the performance upgrades to my 80 carbs that Mike's suggested plus new gaskets and needle valves. The difference was night and day on my bike. My tank is a 2.5 gallon and it gets about 90 miles or better with a ton of power. A good dip in carb cleaner like Berryman's at walmart about 18 bucks and spray will make your life easier.
! quick question, are they tandem or individuals? But in regards to your original question, 28's fine on 500 or lower not so much on the brutish 650, puts out so much hp for the size phenomenal.