dual mikuni carbs (2008)

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Oct 1, 2007
Hi all,

I want to fit 2 off 34mm Carbs on my Norton 850, does anyone please, have any guidlines for the correct size jets (numbering) and slides needed for basic operation of each Carb?

Thanking you all,

Thanks Ron L,
I would like to install a performance camshaft eg S2 cam: for road use... any other sugestions for a suitable cam would be greatly appreciated, I intend to install larger Stainless Inlet and Exhaust valves , I have not decided on exhaust as yet, as for higher compression, the barrel will be rebored to first oversize which shall give a slight increase.

I am open to any combination of mods that have worked well for other 850 owners!

I am bassically just seeking advice at what these mikuni 34mm
dual carbs are set up with what jets to suit Norton Commando 850's. As a starting point.
I do understand that carbs have to be fine tuned with each application and each type of engine , which includes changes that are made to an engine in different performance mods.

Thanks for all of your help.

I suggest you go to Mikuni and download the VM manual to get some picture of what the circuits are, or any comments won't mean much.
Do as Panic says. He has a lot of know how.
Unless you are going to a radical cam and big exhaust system with most of the increase in power being a the top of the RPM I would start with smaller carbs.
Two 32mm are big for all around street use. You may be able to do 120 MPH with this set up but... A pair of 28MM will give a lot more power off the line and with Some UFOs they will not give out on the top. You need gas speed not more volume. Bigger is not better for most of us. Consider that any 600.00 ragged on 600CC modern bike is going to smoke you anyway, so tune it to kill such bikes off the line and in the tight and twisty stuff. This is doable because it's a Norton. Buy Panic's tuning book for Mics about twenty well spent dollars.
norbsa48503 said:
Do as Panic says. He has a lot of know how.
Buy Panic's tuning book for Mics about twenty well spent dollars.

oh yeahhhhhhhhhhhhhhhhhhhhh!!! couldn't of said it better - love that thing
Okay, 32mm Mikuni carbs would be more practical! does anyone have any jet specs on these please?

Where do I find Panics Mic tuning book? got a link out there!

Thanks for all advice, I take all opinions with respect.

Go Aussies!!!!!!!

There is a "lazy" advantage to using large carburetors - it's easier to pin down which circuit is in play, since each covers a wider range of engine speed. With 2 × 28, you're using the float level, pilot jet, idle mixture adjustment, slide cutaway and needle jet size and needle taper & position at 50 mph. With a larger carb the needle is "invisible", which may help or shorten diagnostics.

Easiest: if you have carbs now, what jets are in them?
If you buy a commercial kit from a known source they're generally close enough to run out of the box, how close you get depends on your patience.
Biggest mistake: buying generic carbs, then $pending on tuning parts - very costly.
Mikuni are indeed a good carb (I think they were made under licence from Amal) If I remember correctly twin Mikunis are a little too wide for a Commando and you may have to splay them out making filters hard to fit, some one will have sorted that out by now though.

I have twin 34 Mk2 Amals fitted to my Mk3 850, 3S cam etc. Set to book 'cept one up on the mains, they just work well.
Thanks Guys,

I dont have carbs at the moment, however I have placed a order for the Mikuni VM tuning book. with the link that has been so kindly provided.
There does seems to be a lot of valuable information provided inside that book!

Thanks again everybody.

My FCRs are 35mm. They work great on the Commando. Don't know to what extent you can extrapolate from that with respect to the Mikunis, but FWIW....
Hi Brewer,

If you need any expert hands on Norton help in Perth WA, call this man -Kelvin Mears 9362 4620. He's got 20 years of shop experience and a ton of parts and knowledge at his fingertips.

040 968 9403
Wherabouts in Perth are you? I'd like to have a chat before you get too carried away with big valves etc. Your shout for the coffee.
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