Rebuilding a classic Mikuni carburetor! (1977 Yamaha XS750) - Rick's Garage - ep 29

Hello Everyone!
Today's episode is going to focus on QuaranTina. (She's been feeling left out lately. haha)
If you have an old motorcycle, or even a newer one that's been sitting for a while - you may need to crack open your carburetors to clean, service or even rebuild them!
The carbs I'm working on are mk1 Mikuni BS34's, found on a wide range of Yamaha, Kawasaki and Suzuki motorcycles.
The rebuild kits I'm using today is K&L-18-2579. These work for the 1977 Yamaha XS750D - If you have a later model XS750 with mk2 BS34's, you'll need the K&L 18-2662 kit.
If you're already familiar with how a carburetor works, you can skip ahead to 3:10 to jump right into the rebuild!
This was a lot of content to squish into 11 minutes but I hope you find the video informative, helpful and entertaining!
Be sure to like, comment, subscribe and tell a friend!
As always - Thanks for watching!!
Insta - @rickthewelder170
Love the hat? Get yours today at:
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Intro music sampled from "Beast Inside Me" by Vo Williams

[@fuckinmoron3230]

This deserves far more likes, thank you.

[@mattcc6603]

You've got the right skill set for these instructional videos which is key for those of us who are learning - it's a pleasure to watch, thanks.

[@Stealyourtone]

Wish I saw this before I started cleaning my carbs... So many helpful tips and advice. Great video!

[@whalley1390]

I just bought a 77' XS 750, thanks for the info Rick!

[@spencerblair4110]

This is by far the best carb cleaning video I've seen and the most detailed series on an XS thank you so much. Please continue to post videos of QuaranTina it's helping me tremendously.

[@aidanfeehan4916]

YES PLEASE DO NOT STOP/ MAYBE A VIDEO ON REPLACING AIR BOX TO CONVERT TO POD SYSTEM?

[@crkalinowski]

Awesome explanation of how a carburetor works! It takes skill to teach things well. Thanks for the good video!

[@9194Bustealth]

Hey man, great videos. Also building a 77 xs750 and looking forward to more helpful videos!!!

[@benbaribault424]

Sheesh man I feel like I should have paid for this video… very well made and is going to save me a ton of headache with the extremely crusty set of xs750 carbs I’m about to tear down

[@RicksGarage]

Thank you very much for the kind words! I'm very glad you found it helpful. Be sure to tell a friend about the channel! 😎

[@StarChasershere]

I bought mine used a 1978 xs750. She had 10k miles and expired in a fire in our town with 89k miles. After the fire some parts were reusable. I found another one, same model for $250.00 with 11k mileage and very clean. Everything was rebuilt to specks. The carb syncing with vacuum gauges and replacing the 3 Diaphragm Assembly's in the carbs is a must have, 2F3-14940-00-00. After 40 years these are DEAD, replace them with NEW ones. This is all very important when slowing down to prevent the shot gun effect that will harm the motor. I like the long runs and during hot days you can hear knocking going on when you get off a HWY run like 100 miles. The xs850 has the oil cooler on them and the 750 will work too, plus you get one half a quart more oil. It's a must have to reach 89k with no problems. My bike has a full dress, 3-1 exhaust, cruise control , Vetter Windjammer tall windshield with leg lowers and the Vetter sound system with small amp with micro-card music to headphone in helmet, speakers when stopped, front forks springs upgrade, 850 pull back handlebars (you need an extra 6" of wiring added) and you use a rear brake line to the front forks because it's longer, crash bar with spot light's, saddle bags, the large Vetter trunk and a Saddlemen King/ Queen seat with my back rest mod, and Rear air shocks with air compressor. All this is heavy, but she rides without hands on. A few more note's with more weight: Use the 850 slotted brake disk's, the non-slot's suck. Use tubes in Both tires, for the rear one get the thick tube. It takes a lot of pain to insert the front tire tube without punching a hole in it, the back is easy to install. USE THE TUBES, don't be fooled, got a rear flat once and tube's saved her and me. My bike road from California to Florida and back three times. Just a few more miles was 90k and still she looked like NEW until the fire. HAPPY RIDING😀

[@tonyActual]

Awesome. Hopefully I can get my xs750 running this summer

[@micahsmith774]

great video, and quality!

[@aidanfeehan4916]

Really appreciate your videos. You are the man!

[@coppcar]

Tremendous job Rick. Thank you.

[@pushrodfury6644]

Great video Rick, diggin the animations too

[@Therichi1995]

Thank you! This is the kind of video I was looking for

[@AaronHardinPhoto]

This is one of the best descriptions of a carb that I've seen. Thanks!

[@RicksGarage]

Thank you for your kind words Aaron, I'm really glad it could help. Make sure to sub for more content to come. Thanks for your support!

[@spencermorse6044]

Great video!

[@aguieh2956]

Great video thank you for your time and effort.

[@koreanasian217]

Love your XS series vids! Keep em coming=more subs👍

[@AdrianWhyte]

Brilliant video brilliant presenter!

[@chriscollett9276]

Wow, great job on this video! I appreciate the details on theory of operations, and your descriptions were excellent. I appreciate the great work on the bench synchonization process. Keep up the good work. And I agree with comment below that this should have many for likes thaan it does now.

[@RicksGarage]

Thank you very much for the kind words Chris, that means a lot! I really appreciate your support and thank you for subscribing!

[@buddylee6477]

rhanx great video

[@RicksGarage]

Thank you very much for your comment and support!

[@ralphwatten2426]

Don't be "ham fisted" with those idle needles. P.S. Make sure the passage in the float bowl for the starting/fast idle circuit is open. I cleaned my carbs and I had the left cylinder warm up slower than the rest. I was able to remove the start/high idle needle off the side of the carb and it was clean in there so I decided the floats were too low so the tube in the carb that runs down into the bowl was plugged. I got the float bowl off and the orifice in the bowl where the tube runs into was plugged. Really plugged. Float level was perfect. Bowl back on and start 'er up. Wow does it start quick and idle smooth (no more clacking). Moral of the story: Don't forget those cast in the float bowl tubes and make sure they're open or you'll be doing it over. I got lucky it was the left hand carb. At 6:15 he mentions the emulsion tube. That's the tube I'm talking about and it goes into a well in the bowl. The orifice in the bottom of that well is the one. I cleared it with lots of carb spray and a copper wire. It was plugged with something hard, probably corrosion.

[@GBPaddling]

Fantastic, but surely it would be good practice to replace the diaphragms as a matter of course?

[@RicksGarage]

Agreed! As long as the parts are available. I had a really tough time locating suitable replacements at the time

[@annamckinney6622]

I realize people have short attention spans but I wish you would slow down. Pressing out the emulsion tubes (so you don't damage anything, getting the needle valve apart from the diaphragm, info on the pilot jets main jets and adjustments (though the sync info was great). Disassembly at real time would have really helped. Very informative but still have so many questions. Most people these days just replace with cable/slide carbs, but I hear that with the proper tuning the 34's will run just as well.

[@RicksGarage]

Fair points - this vid was more of a general CV carb rebuild that happened to be the bs34s but for clarification, I used a small screwdriver to punch the emulsion tube down and flush with the main body, then the 5mm allen head fits right over top and drives it out without mushrooming it. The needle valve falls out of the diaphragm once it's flipped over. As for the jets, I just popped in the sizes as per the manual. I will probably have to swap them out once it's time to tune everything properly. That all being said, I'm really glad that you found the vid informative! I hope you've subscribed (if you haven't already 😎) so you dont miss any future content!

[@marcusscott9800]

Outstanding Video! New subscriber here, I have a set of mikuni mk 1 carbs off of a 1980 yamaha xs850 and the butterflies are stuck closed. Can you please recommend any tips to free them up and how to separate these carbs for cleaning. There is no c-clip on the end of the rod to separate them, it looks just like a washer and the rod is larger than the washer. Thanks for your help and keep up the great work:)

[@RicksGarage]

Thank you for the kind words Marcus! Glad you enjoyed the vid. As far as your carbs are concerned, sounds like they need a good soak in some oil to free up the movement. Unfortunately, these things often require a painful amount of patience to get working again.

[@marcusscott9800]

@@RicksGarage Thank you so much for your help and have a great one:)

[@Hwang_Over]

Awesome video. I wish I knew about the heads being different. I managed to get all the carbs apart except for the last one. Dumb question, can you just replace one of the three carbs (all similar) or do they need to be replaced in a set? Does order matter? Thanks

[@RicksGarage]

Hi Andrew! Glad you enjoyed the vid! If you're replacing one of the carbs with the same model, it shouldn't matter. A mix of different styles of carb (eg. 2 mikunis and 1 hitachi) could have some unexpected results. The order of the carbs (left, center, right) is determined by the throttle linkages, not the carb bodies themselves, so don't worry if they get switched around during the rebuild. Best of luck with your project!

[@Hwang_Over]

@@RicksGarage Thanks so much for the quick reply. Very helpful and it makes sense. I'm currently starting from scratch and building an xs750 with no knowledge of motorcycles haha. Its been a good learning process and fun to do at my leisure. I looked forward to more of your videos. Thanks again. I'm sure ill have more silly questions.

[@RicksGarage]

@@Hwang_Over Not a problem! Using an old air-cooled platform is a great way to get some experience and learn. Sometimes the older bikes can be difficult to find parts for but they're usually pretty cheap overall, so don't be afraid to experiment a little bit. Feel free to check out the other xs750 rebuild vids I've got (if you haven't already) - there'll be more on the way soon!

[@Hwang_Over]

@@RicksGarage Will do. Subbed to the channel as well. I don't think people realize how much time and effort it takes to make a video such as the ones you are putting up. Thanks again and I appreciate what you're doing.

[@The4Es]

Great video. I have a 77 as well. Where did you find the throttle shaft seals? Legend has it a Suzuki part number will work but I have never run across an actual Yamaha or Mikuni set of seals.

[@RicksGarage]

Glad you enjoyed the vid! The yamaha pn for the throttle shaft seals is: 2A2-14997-00-00

[@The4Es]

You’re a good man. Thanks. Maybe I’ll finally get to ride mine next year.

[@GpunktHartman]

Here the sychronize methode is for lying under fire in a warzone!!! I hate it: Gaming with those " spacers" will cause damage on the sharp edges of the butterfly ... if you not have a vacuumgauge use the smallest gauge of the valvegaptool, depent of there flexibilty. App.: vacuum: The Vacuum to the diaphragm is going true the little bore beneed the needlehole in the bottom if the Slide. So if the carb will run like this, so i presume you did a good job. If not i cut tell you why ...

[@Afr00t]

Hey rick! Is there a possibility that the choke plunger could leak? Any o rings in there aside from the dust cap? I have the same BS34 MK1 and it leaks/whistles and the whistle goes away when the choke is activated

[@RicksGarage]

That's a weird one - i believe there's just the cap on top - if the plunger itself is very worn, I suppose it's possible that it could develop a leak (although I've never experienced that particular issue)

[@logannevins1959]

I have a very important question! Are there any external distinguishing features to tell apart the mk1 from a mk2 without disassembly?

[@RicksGarage]

Hi Logan, thanks for your question! The choke is the distinguishing factor. An mk1 plunger operates vertically, while the mk2s plunger operates horizontally. Hope this helps!

[@GpunktHartman]

The easiest way is a scale ore youre personal skill to feel different Weights: the MK I is apprx. 1 kg heavier then the MKII. Compare it with one in each hand☝️🧐👍 Also the MKI looks trouly more massive ...

[@krystylc]

Any suggestion as to where to find throttle seals? Thanks very much

[@RicksGarage]

Hi Larry - you can probably still find them on ebay or yambits- The yamaha pn for the throttle shaft seals is: 2A2-14997-00-00

[@beano21st]

hey mate. thanks for the video.. quick question, you mentioned that if you break the tiny tip off the pilot screw it is almost "impossible" to get out. is the that like almost impossible or impossible impossible. a friend is dealing with this exact problem. cheers from new zealand.

[@RicksGarage]

Glad you enjoyed the video Brendan! Removing a broken pilot screw tip is *almost* impossible. The tough part is removing it without opening up the hole in the casting. Soaking with penetrating oil and using compressed air or a small angled pick has been known to work. 😬😬best of luck!

[@StarChasershere]

I rebuilt my carbs and found two of them had tips broken off. Sit them down and use a very small drill bit with needle pliers. On the inside just push not drill. Got mine out

[@huskerbeaver]

Any particular advice on removing the butterfly screws? I have a set of JIS screwdrivers but didn't know how difficult these are to remove with the back ends peened from the factory?

[@RicksGarage]

Those are tough ones - if they dont want to budge by hand, you may need to look into a small impact driver.

[@pauldelay6725]

Where can I purchase the diaphragms for my 1977 Yamaha XS750-2D? Do not want the whole diaphragm assembly.

[@RicksGarage]

I believe JBM industries used to supply replacement diaphragms - the website hasnt been updated in a few yrs, so an email to them would be recommended first

[@dv8music]

Where did you get those replacement brass fuel tees and what is the proper assembly for the mixture screw? Is it o-ring, spring, screw or spring, o-ring, screw?

[@RicksGarage]

Hi David, I picked up the fuel tees on ebay - www.ebay.com/itm/YAMAHA-FJ600-XS750-XS1100-CARBURETOR-CARB-BRASS-FUEL-TEE-FITTING-2H7-14988-00/291777911109?hash=item43ef519945:g:RuoAAOSwsB9bmUxY The proper assembly of the mixture screw is spring, o-ring, screw. Thanks for watching! Hope you've subscribed!

[@mudderfawker069]

@@RicksGarage regarding the o ring on the mixture screw, i do not believe there is an o ring, one doesn't come in the carb kit, there isn't one in the repair manual carb breakdown diagram, i just tore down a set of carbs that were never touched and no o ring. Also I had to buy the o ring for the tube separately from a xs650 site because that also does not come with the carb kit. Kit did come with 2 springs for the mixture screw

[@RicksGarage]

@@mudderfawker069 that's interesting- although the o-ring isnt shown in the parts diagram, my carb kit did include one, and the old needle had one (in the same order of assembly as in the first reply) When you disassembled your carbs, did your idle screw not have an o-ring? Also, several image searches show the order of installation: o-ring, spring, needle. So I stand corrected on that 😳

[@dylanstonecipher8419]

Hi Rick my bike won't idle and won't Rev above 5500 rpm when it's supposed to be 8500. What should I change. It's a 78 xs750s

[@RicksGarage]

Hi Dylan, sorry to hear that you're having troubles - unfortunately, it could be a few different things - off the top of my head, it sounds like your getting might be off (presuming that the carbs are clean and everything else is functioning correctly. Sadly though, if the jets are too big (or too small) the symptoms will be similar to what you've described. A good place to start would be to read your spark plugs. Google the method (too long to type out here) and you should be able to get a better idea if the bike is running too rich or too lean. Then readjust the jet sizing accordingly. Hope this helps!

[@axisvaporhoningindustries4312]

Vapor Honing and they would be better then new although they still have to be completely torn apart

[@RicksGarage]

Agreed but you can't beat the $75 price tag on that ultrasonic cleaner!

[@s.sullivan5299]

@@RicksGarage which cleaner do you use? I'm looking at getting one. And there's a lot of choices. So I'm looking for real input not Amazon fake reviews.

[@RicksGarage]

@@s.sullivan5299 I was using a 25% concentrated solution of simple green. If you do the same, make sure to rinse the parts as soon as they come out to avoid discolouring.

[@s.sullivan5299]

@@RicksGarage thank you. I started pulling mine apart yesterday and for sitting in a garage for 34 years they look shockingly good.

[@s.sullivan5299]

@@RicksGarage and did you get that ultrasonic cleaner off eBay or Amazon?