How to clean the Yamaha XS400 and XS650 Mikuni BS34 carburetor

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[@agentnuget]

A helpful tip for things like jets my dad always told me: use two fingers to tighten, then turn 1/8th of a turn or so past that point. Also ultrasonic cleaners work great for cleaning carbs, as long as you're doing a full rebuild and are planning on swapping all the gaskets.

[@revampedtechnique1164]

Short sweet and informative 👍🏽 Appreciate it

[@ondatsb]

What should the height of the float be ?

[@isaacdeneef7080]

Nice video best one on KZbin thanks for the help

[@gnarsicle445]

Awesome dude, thank you!

[@ezecapo90]

love your videos, but i suggest skipping out on adding background music

[@RiderForge]

I agree. I will definitely work harder on production quality in the future as well. The how-to videos will definitely not have constant music in the background. I appreciate the feedback!

[@J.S.McDuff]

@@RiderForge good to see a KZbinr listen to his audience love your videos bro

[@danield5731]

ola me podrías explicar como poner a punto los platinos en algún video gracias

[@rebelsbaseballizbom]

Do you have any tips on replacing throttle shaft seals for these carbs?

[@LobotanyPictures]

With "High Definition" AND suspenseful tetris music! If this is the first clean and you wanted to emerse the carbs in a cleaner, would you recommend taking more apart?

[@RiderForge]

Be careful soaking them; there are hidden plastic parts that can be vulnerable to solvents. Honestly, I'd just use compressed air and carb cleaner!

[@adrianenciso1761]

i had a same crbs but it always had an overfow of fuel

[@roberth5611]

How do you remove broken needle mixture screws? Asking for a friend, LOL.

[@luiscamacho4256]

My 1978 gs 400 is now straight pipe....same exhaust diameter exit has thé original ones..... do i need to change jets on there or whit that air/fuel adjusting screw i can get a suffisant adjustment!!!!! .... Nice video by the way!!

[@RiderForge]

Luis Camacho straight pipes definitely need jetting. You will likely need to change the pilot and main jet. It's also possible the needle height will need some tweaking. Best bet is to search the forums for your bike and look for someone with a similar setup that posted their settings. This can save you a lot of tuning.

[@weeverob]

great video, tx. on my right carb turning the newly installed fuel/air screw [ and fresh o-ring ] does not change the idle at all, not a bit whether its screwed in all the way or out all the way. does that sound like a clogged pilot jet? tx!

[@RiderForge]

It could be a clogged circuit, yes. Also, ensure the old pilot jet tip did not break off into the inlet; this happens when people tighten them down too much. Are the pilot jets also new? Are the tiny holes in them clear? Sometimes I pull out the jets and air screws and spray carb cleaner in there; then blast it out with an air compressor. I made a little rubber tip for my air sprayer fitting; it really clears everything out! Other things can affect the idle too; the butterfly valves; the carb synch, the fuel level in the float bowls, the air filters you're using, the valve adjustments, the timing... and it goes on and on.

[@dannyboy163]

HELP PLEASE!!! when I was taking mine apart, only one of the diaphragms had the small shim and spring for the needle!! Is this normal, or is there supposed to be a shim and spring on the other one too????

[@user-mr3mf8lo7y]

Just a quick question. Do you ever lubricate any (internal) parts of a carb? Perhaps, not needed since fuel with oil is circulating, or, may clog stuff out. Just wanted to make sure.. Any thoughts on that?

[@RiderForge]

Ken To good question. There are a select few areas of the carbs I would lubricate but these generally don't come up during a routine cleaning and they are technically external. This includes the choke rod, the butterfly valve "rod," and the throttle cable insertion point that pulls on the butterfly valves. A sparing amount of lubricant can be used in these areas where metal is moving against metal. Think of it more like lubricating a door hinge. Any parts like that can be greased lightly so they move easier. Anything internal shouldn't need lubricating and since gas is a great solvent anything you do add will be very quickly washed away or worst case it might clog things up.

[@FuckinPrawns]

hey thanks, super informative. what do you do if you strip the head on the pilot jet? asking for a friend....

[@RiderForge]

FuckinPrawns Decide if it is necessary to remove; often times you can clean the pilot circuit THROUGH the jet without removing it (use carb cleaner and compressed air). If you need to increase the jet size this won't work of course because it will need to come out. A standard extractor should work assuming it is long enough to reach. You may be able to remove it by hand (no drilling) because it is so small and made of brass. If you go slow, jam the extractor in there and twist it out by hand you should be good to go. Before you start with the extraction dump some PB Blaster or equivalent in there and let it marinate for a while just to make things easier. You can also try hitting it with a little heat using a butane torch. Make sure to clean the Blaster out before inserting the extractor or shooting it with fire. Use the smallest extractor possible to avoid damaging the surrounding threadings as well.

[@FuckinPrawns]

chiangxiong i guess i have to find an extractor small enough to fit. thanks for the help

[@mup1537]

can you link the previous vid?

[@TiberiusStorm]

Do you have a video showing how to get it off the bike? I"m no mechanic!

[@Keedro]

kinda late but, one side my main jet is missing the washer. is this bad lol?

[@Keedro]

does anyone know where to find a rebuild kit for the mikuni carbs in xs400?

[@PedroMata-pk7sb]

Como consigo los carburadores MIKUNI de la xs 650 cc

[@ttwilightzzone]

What was that plug on the pilot jet near the main jet? Mine had a rubber plug on the pilot jet on one of the carbs. I did take it off but the bike runs fine without it. thanks for the videos.

[@RiderForge]

Later models came with rubber plugs; older ones like mine have brass plugs. The pilot jet plugs are literally designed to allow access to the pilot jets. It's a controversial subject because results are very inconsistent when these plugs are removed. Some people run too rich or flood when these plugs are removed; you'll also find just as many people that seem to be able to remove them without consequence. From a design standpoint it looks as though they will prevent excess fuel from entering the pilot circuit without first passing through a small channel linked to the main jet. The thing is, sometimes the extra fuel coming through an unplugged pilot jet at idle is not enough to cause problems. Other times it is. If it were me I would install them or replace them; an engineer at some point created them for a reason. As much as I've tried, finding a true answer to this question has proven very difficult.

[@ttwilightzzone]

I will put it back, but do both carbs have a plug? only one of mine did. thanks. Mines a 1982 special II, btw.

[@RiderForge]

Yes sir. Both carbs should have a plug. Check out xs400.com as well; it's a great site.

[@lurelogan4111]

are these the same carburetors as a 1977 yamaha xs 360 i need a new duel set and im wondering if the xs 650 will work please reply

[@lurelogan4111]

@@PharmacyBrain thanks so much im going to order the parts and ride again

[@ensoroni]

Damn you're good! Can i sen you mine?! lol

[@RiderForge]

Thanks! They're not as bad as they look. Just go slow and be gentle!

[@_Peremalfait]

How essential are the screens under where the float needle is located? I'm afraid while cleaning the screens I damaged one, they are brass and a bit fragile. My instinct is the carb will still work fine, but I'd like to be sure.

[@RiderForge]

The screens are used to filter the fuel, so they are not essential to run. However, I would recommend installing an inline fuel filter between your gas tank and the carbs. I recommend everyone do this, but especially for you if you're missing one or more screens.

[@_Peremalfait]

@@RiderForge Thanks for your quick response. I've ordered a carb kit, 25 bucks, which has the float needle seat screens., as well as new jets, gaskets, and needles. I figure it's better to play it safe, and why not replace these things while the carb is off the bike. Do you have a video on installing an inline fuel filter? By the way, thanks for this video which was of great help to me in cleaning the carb on my 79 Yamaha XS400.

[@RiderForge]

@@_Peremalfait Good call. I don't have a specific video on that, but it just involves cutting your fuel line and jamming the filter in there. It's good practice to use clamp fittings for security. You just want to ensure it's a small filter designed for a carb (and not a fuel system with a fuel pump which generates a lot more pressure). The filters are also directional. The next "gotcha" is ensuring you have the correct size filter for the size of your fuel line; you will want to either measure the inner and outer diameter of the fuel line or confirm with someone on your model-specific forum.

[@_Peremalfait]

@@RiderForge Sorry to bug you again. I got a carb kit for my BS34. The kit didn't include gaskets for the float needle seats. Do I need to get some? The old seats appear to have used a flat gasket, but there's not much left of them.

[@RiderForge]

@@_Peremalfait You may just want to try things with the parts you have on hand right now. Taking the carbs off and apart doesn't take too long once you've done it a few times. I did it so many times I was able to get them off, adjusted, and back on in under 10 minutes! Anyway, I will say that the bs34 carbs are "fickle" and even the tiniest imperfection may cause issues. Worst case scenario you fix the parts you have yet to replace. Good luck!

[@VasilisKampouris]

Hey man I have an XS400 78' I want to put mechanical carbs can you recommend some that they fit? thanks in advance :)

[@RiderForge]

I have seen a few carb swaps (including a single carb setup) done over the years on the forums, but this requires custom fabrication of intake manifolds and/or brackets. To my knowledge nothing bolts directly up. Are you looking for a bolt-on solution or is fabrication an option?

[@VasilisKampouris]

I really do not know! I just got fed up of my bike not starting on easily and though of moving to mechanical carbs. But i do not know exactly what i have to do. SO i think i am looking what works best. And maybe the steps I should take.

[@RiderForge]

For the bike to start easy the carbs need to be surgically clean and the timing needs to be perfect. If you adjust these two aspects you may get the results you're looking for. Mine always started first kick.

[@aanpermana]

Is there a way to clean the carbs (just to make it clean enough to operate properly) without having to re-set the mixture screw and re-sync the carbs afterward?

[@RiderForge]

I would recommend pulling the mixture screw out for cleaning but you can certainly avoid syncing the carbs initially to just see how it goes. Adjusting the mixture screws is super easy.

[@aanpermana]

I wish you could make a video on that. After cleaning, we should adjust the mixture on each carb individually, and then sync them, right? I went to some shops around my place, and they said old carbs like mine are usually hard to setup.

[@RiderForge]

Old carbs might take longer to clean because they've been neglected for years. Parts can also be more difficult to locate. Some customers might get upset about this and blame the shop for the bad experience.

[@Xm0n]

has anyone found main air jets for this carb? I've been looking for months, my bike was missing one when i bought it

[@RiderForge]

mikesxs.com

[@mugglesmoiks]

awesome! Did you clean it after you took the emulsion tubes, the pins, the float needles, basically once you disassembled everything thing in your video?

[@RiderForge]

I cleaned everything off camera on both sides. I just wanted to take everything off as fast as possible in this video.

[@mugglesmoiks]

chiangxiong well..... tried taking the needle off the float bowl and the tower just cracked in half.... now I'm currently looking for a right side mikuni BS34 carb. Haha, just my luck. But the video definitely gave me a good idea of how to properly clean it, thanks again! I guess I've been cleaning it wrong this whole time!

[@RiderForge]

Michael Park That sucks! I've seen a few of those towers crack before. Sometimes the pin gets stuck and it seems like it doesn't take a lot of force to break them. I wasn't terribly impressed with the results I got from soaking in the past. Unless you have an ultrasonic cleaner of course.

[@Farawaystone]

Michael Park May Be a Little Late now, But, I drilled down into the carb body, then, drilled into the top of the broken Tower all the way through. Then I placed a Snug Pin into the carb base and Broken top of the tower and used a small amount of JB kwik weld to ensure a bond. I replaced the Float Pin for alignment while I clamped it to cure and I also used a small amount of Vaseline at the Float Pin so the JB Kwik Weld didn't stick to the Float Pin. It Worked fine. There is no pressure on the tower so it's a Option for repair. I found the Tower Broken when I opened the carb after Buying it.

[@VyantQuijt]

chiangxiong The pins don't just become stuck, some models have a thicker ends to the pin so it is pressed tightly into both towers. When I tried to tap mine out at the first clean, similarly to your technique, the head-end of the pin remained stuck and bent as the tower gave way :( You might want to mention this in the video, as your technique will break more towers when a little more force is applied. Here's the forum thread on broken towers with more info and fixes: www.xs400.com/forum/showthread.php?t=10312

[@francescomorale7570]

Hi, I can't figure out where to go a little ball and a spring, can someone help me?

[@RiderForge]

It's been years for me, but i am pretty sure those are from the choke rod. when you pull the choke rod out they pop out. i don't remember them being hard to put back in.

[@closson91]

Any advice on a stripped pilot jet?

[@RiderForge]

closson91 my first advice is to leave the pilot jet in. If you're leaving the bike stock and it's running fine there is no reason to remove it. Just run carb cleaner through it and hit it with compressed air to clean it out. If you really need to change pilot jets there are a lot of forum posts and videos describing removal strategies. Good luck!

[@closson91]

RiderForge thanks but I'm very familiar with how to clean the carbs. The previous owner stripped it in and I've tried to pull it a couple times without success. I'm just concerned it isn't getting proper flow since its flattened. Thanks

[@RiderForge]

closson91 as long as the actual aperture or hole is not damaged I cannot imagine there being any significant impact on performance. There is a lot of risk involved in removing the stuck jet. Why not test the bike first to see if it's actually a problem before attempting an extraction? Remember the pilot jet only contributes to performance at or around idle and the flow is fully adjustable. If there was a slight increase or decrease in flow just adjust for it. Job done. If you bugger the carbs trying to remove the pilot you may create more problems than you solve, incur more expenses, more down time, etc.

[@CplVasilli]

Song?

[@RiderForge]

If i remember correctly this came from www.lukhash.com/

[@RealSuburbanCowboy]

Great video, SUPER ANNOYING MUSIC! Thanks for sharing.