XS1 carb tuning

Cribby

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Hi

I’ve just had the carbs on my XS1 professionally rebuilt but the bike is running rich as hell

I use a Gunsons gas tester which works great on all my bikes but this one I can’t get any where near the reading I need. No matter how far in or out I move the air screws, the bike still runs rich

HELP!

Ant
 
Hi Cribby,
I know you just paid to have this done but unfortunately you are now in the position of not really knowing what’s in your carburetors. 5Twins has correctly pointed out that most rebuild kits available online contain the wrong size jets for your make and year carburetors. Also you have no way of knowing if the float height was correctly set and I’ve bought new gaskets that don’t fit without a lot of trimming. Did your builder install new jets or just clean everything up?
2M posted about how much is original jets had worn, increasing the size of the jet.
F1D51025-2135-43EA-AAB8-58BA2F179737.jpeg

I myself installed the correct size pilot jets on my XS2, but they didn’t have the aeration holes on the sides like they were supposed to and my bike ran like crap until I figured it out.
28B2A33B-20FF-4CFD-B5E6-E438D44A3764.jpeg

These carbs are so touchy about being properly set up. I just don’t know how you would proceed until you see for yourself what your jetting is and how your floats are set. Gary always like to recommend doing a hot water dunk test on floats to look for bubbles.
Some guys here are real pros with carbs. But for me, it always seemed , I had to install / remove/ inspect / re install a few times before I got everything working right.
Good luck, maybe someone more knowledgeable will chime in.
 
Click the Tech button and find the link to the old carb guide. It will give you year-by-year specs and components. +1 on checking floats and fuel level; when there's no response to mixture screw changes, that's the first thing to look at. Avoid kits and knockoff Chiwanese brass; genuine Mikuni parts will save time, aggravation, and money.
 
I'm running that XS1 I stole from under you, :rolleyes: All stock pipes airboxes and new stock jets. All is good.
credit 5twins 4 images
CarbSpecs.jpg
mikunipilotjetsmoddedam2.gif
 
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GENUINE MIKUNI brass cost a fortune. Mikuni sells their carbs with brass that works on nothing
and then make a fortune selling you what you really need.
 
There's no such thing as a bolt on and run it aftermarket carburetor ,there are just to many engine variables in question unless you buy from 650 Central where the jetting will be very close. In regards to Mikuni selling carbs with jetting be off, you need to buy from a distributor who will work with you on exchanging the jetting or offer some discount on the jetting.
 
GENUINE MIKUNI brass cost a fortune. Mikuni sells their carbs with brass that works on nothing
and then make a fortune selling you what you really need.

Dunno? stock Yamaha Mikunis seemed to work pretty well as jetted. ;)
I buy genuine mikuni brass, often from Niche supply, not that expensive, I prolly have over a hunnert jets by now. :shrug:
 
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I wonder how much the properties of pump gas has changed over the last 50 years. Surely it has changed enough to require subtle (or not so subtle) changes to carb jetting and tuning. Maybe a step or two up on pilot jets can improve things? At least ethanol mixed into gas effectively leans out the mixture. I once dumped a liter or two of E85 into an over half full tank of Shell V-Power 98RON. And the bike would not run properly without a little bit of choke.
 
Just to clarify - I was talking about the aftermarket VM.s not the stock CV carbs.
I believe you need to list ALL jet sizes, including needle jet, needle size and slide cutaway. And carb size (32/34/36/38?)
Some background info would also be helpful, i.e are the carbs used, or purchased new for your XS, and so on. It is very possible that VM carbs come with a baseline setup for a 2 stroke......
 
I keep a variety of jets for stock and modded bikes to fit BS38, BS34, and the VM series of Mikuni.
When I mess with other brands of carbs I'll buy jets for those.
If you use carbs and want it to run right that's what you do.
I'm not a great tuner but I get by with a little help from my friends.
 

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