34mm mikuni's on a 903cc?

I'm considering the mikuni 34mm VM RS carbs for my 76 900. My bike is basically stock except for a 4 into 1 header, dyna elec ingition&coils and air pod filters. My goal is good driveability and a slight performance increase. From what i've read they can be jetted down for a stock bike and perform great on the street, is this true?. The carb kit cost around $1200 so before i spend my hard earned cash i would like to hear some feedback from any members that have expierence with these carbs, thanks.

34mm is too big and wasted on a 900 , even if it was tuned.
You will get better performance with 28 or 29mm and no loss of bottom end drivability or top end restriction.

68dave wrote: I'm considering the mikuni 34mm VM RS carbs for my 76 900. .

I'm kinda confused :blink: it happens... I'm old
Are we talking about Mikuni VM carburetors


or Mikuni RS carburetors?


They are entirely different animals? :dry:

I have then and from what I have experienced in the setup of my bike, I would not recommend them for your bike.

Way to much carb for the CFM flow of head.

My fault, the RS carbs. I've had issues with the older carbs and thought that carbs with newer technology would perform better. I may just have to find somebody to go thru my 26"s. I purchased this 78 1000 with 29"s for $500, then i sold the 29's for $550 on ebay so basically the bike was free. But i shoulda kept those 29's!

68dave

What you are doing right now is an important part of understanding your bike and gaining knowledge.

Most of us have and in the future will show our underbelly while giving advise and taking a stand . I have learned a bunch in the almost three years on here.

Don't ever be worried about throwing it out there and seeing where it sticks. Ask a ton of questions, read your manual from cover to cover 20 times as I did. Use the internet and search for material. Its all out there, you have to find it.

Good luck

With a good head, .400 ish lift cams, 1015 piston kit with 10.5:1 compression and a good pipe...... Yes.

On a stock 900 motor......waste of money unless you're going to build the motor down the road. For what little you'll gain going from 26'a to 28's I wouldn't even bother unless your 26's are messed up or you get a great deal on 28's or 29 smoothbores.

Will they work regardless? Yes but you'll have to control the throttle carefully at low [under 4000] RPM.

Ideally, on a full on performance application, the carburetor bore should be close to the size of the intake valve. From that standpoint the 34mm carb against a 36mm intake makes perfect sense. BUT, those carburetors out flow your stock head by about 49CFM at 10" of water. You're simply not going to take advantage of the potential of the carburetor with a low compression, small port, poor flowing head with dinky little cams...

Now...aren't you glad you didn't blow $600+ to find that out later

Thanks to all for the info. Yea Larry i'm glad i joined this forum so i can gain some knowledge and don't waste my hard earned $$$! I have 2 76 900"s with 26's and both of them run but i don't like the throttle response on one and the other the choke acts up and is hard to start sometimes.

Since i'm a newbie here's a pic of my 900's.

Another pic

strap the 26 on the back bring em up here and I can fix them .