mikuni carb jetting

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Aug 20, 2005
I am trying to get my 850 jetted up right. I have VM36 single mikunii carb, & standard setting for pilot jet is no.35 according to suppliers. I am already down to no.30 & it is still a bit rich on idle, I have sent for 27.5. This seems way lower than standard setting. Does anybody out there know what jets are in their Mikuni carbs, or any related advice on setup?
I can't find my Mikuni tuning notes right now, however if I remember corrrectly I went down to a 25 on a 34mm for an 850. I do remember it was smaller than all the published info and it ran great.
Thanks Michael, I was starting to wonder if I was on right lines as I was going so far from recommended jetting. Mind how you fall
Hi Geoff

I also have a mikuni vm 36mm carb fitted to my 850 commando, at the moment the bike is in bits being re-built, new camshaft pistons etc. I only purchased the carb in august so have not done many miles on it, however I found the carb was running rich with the jets that were fitted as standard.
I have another 3 jets that were in the kit so if you find out what the correct jetting is I would be grateful to know.


Hi Geof/Neil

I bought my bike already fitted with a VM36, it was fitted with a 40 pilot jet and ran very rich at idle even with 4 turns on the air screw. Changing to a 35 pilot improved things but it still runs a little rich with 3 turns on the air screw. I will be trying a 30 pilot next which I think should be about right. The main jet is 260, not sure what the needle/needle jet are.

If you haven't already found the link to the VM manual on the forum then look here

Thanks for the reply Dan and keep me informed on your experiences with the 30 pilot jet.

The carb was supplied with a spare 32.5 pilot jet and a 300 and 280 main jet, I have yet to see what is already in the carb.


I have gone down in stages to 30 pilot jet, & this is still a bit too rich, I am waiting for 27.5 to arrive, so I will let you know result of that. Recommended jet is 35 from suppliers. I am running recommended main needle & throttle slide with no problem, it is just idle that is rich
Interesting topic and advice, guys. I inherited a 36 mm Mik on the 850 and had some rich running problems -mostly on the enricher, which fouls plugs ASAP! Just looked at the pilot and it's a 40, so will order a range of smaller ones to test. Like some of you, I find that the air screw makes no difference no matter how far out I go, even after cleaning it out.
I've just checked the carb and it's fitted with 35 pilot and 290 main jet. I have also been supplied with a 32.5 pilot, 300 and 280 main jets.

I'd ideally like to get the running rich issue sorted before it goes back onto the bike. Can anyone recommend a combination of jets to try? I may have to order some smaller ones from where I ordered the carb if necessary. Someone out there might already have gone through this and have all the correct jetting, I would be interested to hear from them.


The bike is now up and running. With it being a practically new engine I want the jetting sorted ASAP.

Has anyone found the correct jetting configuration for the 36mm?


First of all your ignoring good info on this on the post above by Panic. Base line for all BI are For a VM34; 260 main jet, 35 pilot jet, Q2 needle jet, 6dh4 jet needle, 2.5 cutaway, 2.0 main air jet.
This will get the bike started than read and do the job right someone's carb settings are not your carb settings. No two bikes are the same. The settings are rich you work to lean as you dare. About 55-60 MPG will work you should need a choke to start cold.
Hey guys,all of the foregoing is why I ditched Mikuni carbs. on my Triumphs and Nortons and went back to properly sorted Amal carbs.,Mikunis are fine if you want to spend all of your time swapping jets and doing plug chops -- just an opinion.Ride safely. James.
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