Mikuni BS34 air intake jets/passages

dad, i got new needles with the jet kit. so they should be the stock size. i hope... and thanks chris, mine are the ones on the left. i know that the Hayes manual is wrong about the float height i believe. just dont remember what the dimensions were.

and your welcome for letting you use my online user identity dad. asking wouldnt have really hurt.:boxing: come at me bro! :laugh:

volcom.

Fraped :laugh:

I got sent those needles too, they are wrong. You need to get the original type ones. I got mne from xs650.de = mikes xs
 
Back to your original question about the jet that is non-removeable. I was just looking at my carbs as i just took them out of the bike yesterday and i am getting ready to clean and rebuild them. I think the one that you can remove may be #3 not #4. I was able to thread #4 out with no problem at all on mine however on the #3 i didnt even see a slot for a screwdriver to take it out.
 
Here's a diagram of the internal passages for these style of Mikuni's.

I just noticed that you live in Ofallon, Mo. So do I. Where about do you live? Do you still have your xs400? Have to get together sometime. Hve a great day!
 
as long as we're on the topic:D more diagrams of our carbs
 

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It is normal to have some climb in idle rpm as the bike warms. After i shut off the enrichener all the way (choke) and the bike is still cool having just run for a couple of minutes, it will idle around 1000rpm. After it warms up, it will vary from 1200-1400 rpm (give or take)- and there is nothing wrong with that.

An idle up around 3000 rpm if everything is adjusted indicates a lean condition from adjustment, air leak or idle circuit passages being dirty. I would turn the idle mixture out to 3.5 turns, make sure there is free play on the throttle cable, good plugs properly gapped, just let it idle to warm, then use the idle air screw to adjust to 1200 rpm. If the idle still climbs too high, then check for air leaks. If there are none, the carbs need cleaning.

BTW- the idle air screw should have a spring on it which will prevent it from loosening, If not, get one. Also, if it is vibrating loose, the idle will get lower.

Hey man, I'm having issues with an air leak I think in my right carb. I've got a '78 400 with stock bs34's on it. I've had the carbs apart many times to change the jets. I've gone up 2 sizes on the mains which seems to be perfect for top end, the pilots are still stock but I've got a set of 1 size up. As soon as I start the bike it revs up to I'd say around 3-4 grand. I don't know for sure cause the tach's been taken off. Anywhoo... are there specific problem areas I can check 1st? I know the intakes are good and I put new idle mixture screws in, I've got uni air filters and chopped down stock exhaust and the diaphrams seem to be mint. Can you tell me which passages I should check please and thanx dude.:)
 
Have you synced the carbs yet? Also make sure the idle mix screw holes are not plugged. The screws tend to get broken off inside.
 
With your setup I would use 45 pilots set to 3 turns out as a starting point.
 
Have you synced the carbs yet? Also make sure the idle mix screw holes are not plugged. The screws tend to get broken off inside.

yeah I bench synced them and replaced the idle screws because one was busted off in the carb and I was lucky enough to get it out. And a 45 pilot is whats in them now. The screws are around three turns out now and it runs great except idle. Are the holes described at the start of this thread of concern when trying to get a low idle? And what about timing, do you think that would give me a high idle?
 
You need to sync them with a gauge or manometer trust me:thumbsup: Also timing would affect all rpms if it was way off. I think the screw that broke off in the carb is the issue did you drill it out or did it just pop out easy? The holes are tapered to seat the needle if it is not the correct taper then it will not work right.
 
Very funny.

yeah I got the busted needle out pretty easily. And I just totally cleaned the carbs out again today and put in the 45 pilots in and it runs like a total bag o shat. I hope that maybe it's the timing cause I checked the plugs after a little ride and one was really lean and the other looked good.

I tried searching for a timing thread and no dice... do you know of a good one?
 
Hello! I am desperate, because I cannot find a carburetor diaphragm spring for my yamaha xs400 1979. Does anyone know the measurements? Can you advise me where to buy them and which other model fits? Thank you
 
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