Vacuum Synching Your Vintage Honda 4-Cylinder Motorcycle Carbs - pt.2 - CB350F, CB400F, CB550, CB750

[@jcx5659]

These are some of the most well done videos I have ever seen on YT. Congrats on the quality and professionalism you put into these. I'm very impressed.

[@lundyracing]

Wow hit the nail right on the head. This is really going to help out newbies. But rather than only using one gauge, first connect your gauges to a 5 way splitter, and then one carb and sync your gauges, before you sync your carbs 😉

[@tomclayton6875]

Got a friend who bought an '84 650 a month ago for $2500 and is rebuilding the carbs. Gonna forward him this video. It's a beautiful bike but has been sitting 5 or 6 years with 11K on it and needs some TLC. Thanks for your demonstration.

[@SY1WEK]

Probably the most satisfying video i've seen on youtube. Thank you for the detailed explanation of the entire process!

[@joeheydenrych1240]

Cheers mate, very in depth explanation you've done here. Well done.

[@murraykriner9425]

Really hope the community takes note of all the steps. Its not Black Magic like the Fuel Injected boys believe, just a careful considerate manipulation of the factors that effect the tune. Great job!

[@BounouYoucef]

Masterful, Well presented and simplified. Respect to you sir.

[@rikmiles6531]

Wow that was so well done. I have owned 3 cb750 ‘s and I definitely botched the synchronization of those carbs back in the day. You made this video so well it think ( hopefully ) anyone with half a brain could follow your impeccable directions. This was so easy to understand. Well done, well edited, nice graphics, great sound and lighting and above all no dumb ass music and you got right to the point.⭐️⭐️⭐️⭐️⭐️

[@shawnmahmoudi8705]

OK so you all helped me out so much. My CB550 has never been this happy. Thank you.

[@doctordapp]

Thank you! Have the valves here (from my wife's previous aquarium air bubbles). Will get a vacuum meter, a valve and some hoses soon! Then I can adjust rebuild my rusty tired xj900 and bring it back to life!

[@Rocksoup77]

That's great info. You answered my question early in the video about the older style carbs not having a "reference carb". Working on 73 cb350f and wasnt sure about that. Thanks!

[@lee.stubbs]

Great video, thanks. One recommendation would be to use a five port manifold instead of four so that you can turn a valve to clear the vacuum instead of the rubber cap.

[@Common-motor]

great idea, especially with how many times I've dropped the cap haha

[@Danny_6Handford]

Thanks for making this video, very well done and very informative. I did the carburetor sync on my 1976 Hondo CB750 with the older style carbs last year using the 4 vacuum gauge set. I did not realize that the 4 vacuum gauges may not be calibrated to read the same value for all 4 gauges. After watching your video what I did to check to see if all 4 of my gauges where calibrated was measure the vacuum on cylinder one with each one of the gauges and they all measured the same value to within a couple of millimeters. So I think my 4 gauges were pretty well calibrated and I do not think that I need to do another full carburetor sync. The engine runs smooth and it starts up from cold no problem and it idles real good at about 900 RPM.

[@bldeagle10]

Well, buying this sync kit right away. Time to get the CB350F tuned perfectly.

[@rayestanley517]

What if you don’t have a rev counter?

[@bldeagle10]

@@rayestanley517 id buy a cheap one off amazon or 4into1.. kinda necessary if you really want to dial in your carbs

[@SailorSam41]

Mercury stix seemed simpler to operate, and with every adjustment you could watch the change in all cylinders simultaneously. Just be careful not to rev the engine or the mercury would be vacuumed through the intakes. Saw this happen and learned my lesson. Also the final recommendation was to have the two outboard cylinders pulling a bit harder to allow the inboard cylinders to loaf a little and run a bit cooler. My first bike was a 1980 GS 550L Suzuki, and it started just like your Honda. Kept it for 30,000 miles and never should have let it go. Same for the 1980 CB 650 Honda I inherited back in 2000. Absolute dream of a motorcycle. Wish I still had it. Enjoyed your videos. Brought back many good memories (as you can tell). Thank you for posting.

[@kevinproctor8743]

Excellent instruction. Much better than others I have watched. Well done

[@astalavisitor]

So much detail and intuitive video editing its just mind blowing. Added this to my DIY playlist, licked and subbed.

[@KaranJeffery]

Adjusting the air screws after balance gets these bikes super smooth,

[@ScatManAust]

Hi Brandon , You have just made the penny drop for me when it comes to the gauge sets especially when I used to sync my CBX's . trying to use a pair of quad gauge sets With no certified calibration going on in the shop, it was a tall task expecting all the gauges especially from two sets to all be reading the same and just did not occur to me at the time. As such I had better success with the hose and using my calibrated ear on the six's . Brilliant explanation and step by step video . cheers

[@063317Art]

Use the same method on the GL 1000 and the GL1100 and the GL1200. I used 4 vacuum oil dampened vacuum gauges from McMaster, Double checked that they were in sync with each other. The oil in the gauges slows down the needle bounce a lot. I had a 1998 CB550K like the one in the video and a 1985 GL1200

[@60swanny1]

Outstanding videos. Covered all the major types of carb setups. I have a Honda CB350F, the tutorial works like a charm. Thanks!

[@stevehammel2939]

Thank you for the video, even an old mechanic can learn something of value

[@rburrill7236]

Very good video. learned a bunch. Now it makes sense to use one gauge to sync. thanks. now need to find that 4 into one vacuum splitter

[@plusblood5101]

I rather have 4 gauges for each cylinder That way its faster Your single gauge and gang manifold is time and unnecessary work All four gauge system reflects on coresponding cylinders View the readings blip a few times Tweek and done But your sync details are gr8 Thanks

[@baxrok2.]

Very impressive tutorial. Great explanation, camera work, and graphics. Thanks!

[@alansemple2015]

Great video, your explanation made a lot of sense. I think I will let a professional do my K6.

[@tonybell3404]

Hi great video personally I like the Morgan carbtune it's based on the Mercury type gauges and it seems more stable used it to set up a 1992 Triumph Daytona 1000 runs brilliant now

[@Common-motor]

we will have to check it out!

[@bretearwood7027]

I bench synced my carbs by just observing how much light was getting through the butterfly valves and I am super surprised how well the bike starts and runs at the moment. I cant wait to sync them with a guage to see how close I got them.

[@mannygomez5971]

Kudos 👍 lil details knowing the early has no set carb

[@tonymontana897]

This has to be by far, the best carb syncing video I have found. Thank you so much for an outstanding video. The information is clear and concise and very informative. I've never had to do this job, but I find myself now having to do it soon, so your video will help prepare me a bit. I have the traditional 4 gauge kit which I have never used but I am going to try the single gauge method with the 4 way valve. I am wondering if a non return valve can work in place of your dampening valve ?? Will the one way valve stop the engine pulsation ? I have a 2001 Kawasaki ZX9R which is going to need the whole enchilada, that is, first a valve clearance check, a full carb clean and then the synchronising. Wish me luck ! P.S. My like made it hit 1000 likes lol..

[@lotophagi711]

Used to use a piece of hosepipe to sync the carbs on my Kawasaki triple. Used it like a stethoscope and listen to each carb air inlet in turn.

[@ScatManAust]

That's how I use to do the job on my bikes and customers bikes. I have done this method on my Jaguar and many multi carb setups on cars as well. In fact my genuine Jag manual actually shows and describes this method as well as another little bit of info, It recommends a litre of methylated spirits in each petrol tank once a month to remove water from the tank and fuel system and keep it dry. This method works very well and served me well, as well as the tripple and quad gauge sets. Its ironic that Brendan said that not to use the multi gauge sets as I found I had more reliable results with the ear and hose trick than using the combination set. Especially so with my CBX's because I had to borrow a second set of gauges to do the job. I found I could get better sync with the hose on the six's. Makes total sense now trying believing all six or eight gauges would be equal . I now think not . Workshop tool calibration was not a big thing back then but it certainly is now and can be very costly getting them done every year or two to comply with standards and accreditation. My preference is still to use the hose and ear trick or the manometer, but if the customer or friends are looking over my shoulder and they think they know it all , I will use the gauges to please them.

[@Common-motor]

@@ScatManAust Haha yeah definitely. Sounds like your customers should trust you more, CBX's are monsters to tune! We like to teach this one gauge method because it's foolproof and removes a lot of variables and user error. For someone who knows what they're doing though, there's plenty of options like the hose and ear method. Thanks for the info, and does the metholated spirits just go right in with the gas?

[@ScatManAust]

@@Common-motor It goes well . Its much like methanol and ethanol, being hydroscopic it will take on the water and being mersible in petrol, will pass through the carburetors and so dry the tank of insoluble water. Obviously it wont work miracles with huge amounts of settled water but used on a regular basis will work as Jaguar state. And when it comes to EFI systems then I cant see any problems there as the ECU will compensate. As far as working with diesel, I have never tried. I certainly would not try it in a common rail system but the old conventional plunger and rotary dpa pumps may work. I still use methylated spirits to this day albeit once a year in most of my vehicles. Actually another great use for it is to clean all the plug leads, boots, coils and distributor caps inside and out . Doing this drastically increases the life of the system due to not jumping and tracing, but the biggest benefit is from not drowning the ignition in the rain or cleaning the engine.

[@Common-motor]

@@ScatManAust ill have to give it a try in my tanks!

[@jerome8469]

Thank you for these vids , I always wondered how it was done , Now I know , But when the opportunity arises to do this I’ll need to rewatch vids x’s 4 or 5 times lol there’s a lot to remember 😁 Love & Peace your way brother!!

[@stephanebelanger9310]

Thank you, very time generous video. You guys are pretty passionate about bikes and it shows.

[@mattmf01]

Great video guys. Love my CB750s

[@knobon]

Thank you for a great easy to understand video, going to help me a lot and give confidence to do it.

[@tsoliot5913]

My god, that's the same year and model of my eternal project bike. Now I just need a video on wiring it.

[@Craig_McWilliam]

Thank you for posting these - really useful and clear instructions!

[@ptposeidon]

Very informative. Thanks for the help 😍

[@douglascary9280]

Thanks Brenden! Even though I have a 360 (2 carbs) I got some good tips for doing mine. Appreciate all you videos. FYI Finally got mine on the road and running GREAT!

[@Common-motor]

Ooo send us photos to the support page on our website we’d love to see!

[@marcusscott9800]

Outstanding video! Thanks for your help and clear explanations of each process.

[@johansilva4888]

Saludos desde Venezuela, Buena clase de como sincronizar los carburadores... Gracias

[@DutchedShedBuilds]

Really enjoyed that. Great tutorial👍

[@sieve5]

These videos are SO HELPFUL! Thank you!

[@CrashHardEnduro]

This was great! You guys have a new subscriber.

[@joemehen7881]

Very informative I appreciate you 🙏

[@danmcneil7181]

Thanks Brendan. I happen to be struggling with the tuning and sync on my 75 cb550 and this video has helped alot. Mine doesnt have a reference carb so I guess I'll be using the trial and error method to find the appropriate carb to reference from. Very good video.

[@preez77]

bench sync all carbs and don't adjust #2, boom! you have a reference carb!

[@Common-motor]

Definitely a bit more work at the beginning of the sync to know where you are going but we actually prefer the early style over here at CMC. Glad the video could help you out! Once you get two in sync you're good to continue as the later style!

[@TheFtr27c]

Got 1973 cb750. Thanks for the info awesome help

[@dansherman1980]

Goldwing carbs require balancing with number 4 adjustments and then there’s Yamaha’s YICS

[@tatatade]

I like your motorcycle,I feel something artistic,I also sent LIKE👍 I know, We are HONDA lover

[@michaelwhite9845]

Quality and solid info. Thanks boys

[@jimflammer9370]

Great video, thank you.

[@timbotto]

Thanks for the step by step process.

[@colelarson6192]

Wildly helpful, thanks guys

[@dannybear3121]

Both of your videos are awesome thank you so much for the helpful information. I have a question, and feel free to not answer because it is a little bit personal, but why do you have a sin graph tattoo on your arm? I’m just curious. It looks cool though

[@delschier1419]

Good video! Where did you get the four way valve? Using a single gauge makes sense, they are never accurate.

[@Bizzyjjjeks]

What about the AFM adjustment screws, I imagine these need to be in sync before you move to syncing the butterfly valves. In the context that I have had the carbs off, rebuilt and put back on, I want to make sure the AFM screws are dialed and synched before moving into the butterfly/idle speed adjustments

[@Gvictor72]

Thanks man fantastic videos 👍👍👍👍

[@leahmmiller6967]

so satisfying

[@scottpastere9404]

You should get a DigiSync they are awesome

[@flatlandappalachiallc8911]

Great teacher! Thank u.

[@oembol]

Very informative, thanks!

[@austinparsons1785]

Should you sync your carbs before or after tuning them and having the right air to fuel mixture, I just rebuilt my carbs and don’t what what comes first

[@Common-motor]

It shouldn't matter, the air to fuel mixture screw will just be your idle air to fuel. I usually do it after because its easier to hear the difference in rpm change with the bike running on perfectly synced carburetors.

[@purpledraff293]

Hey guys great video. Just curious what brand carb tool you used was. I have a cb900 about to go through all this and wanted to get one. Thanks.

[@ClarkPearson]

Could you minimize/regulate gauge needle bounce with whichever valve you were using on the distribution manifold? They are variable air control valves just like the one you added inline, right? Thanks for doing the video! It's great.

[@Kramabaretter]

Been using a motion pro Mercury gauge for years.... And I can guarantee you one thing they are the most accurate gauges out there.. and that's not the procedure we use... Honestly I can probably get closer on the bench.

[@Common-motor]

everyone has their method! We find this method an easier and affordable method to teach but as long as you are getting the sync spot on with the method you are most comfortable with that's what is important. Heard great things about mercury gauges! I don't trust myself to not suck mercury into the engine though haha

[@Kramabaretter]

@@Common-motor it's not my method it's the proper method...raced and worked for Honda for over 25 years... You won't suck mercury into the bike unless you have some crazy idle going on...

[@racingrooster4642]

Great video . I will try this on my troublesome 400 f. Have I got the patience thats the question ? Thanks

[@connergunnoe5576]

I noticed your kit doesn’t say it works with any of the 650 models. Looking at possibly picking up a 1979 CB650 with the 4 cylinder will this kit and process be the same on that year of bike? It definitely needs the carburetors synced because it doesn’t seem to want to run consistently or smoothly especially without the choke.

[@arniepries6480]

Great Info!

[@raymondseymour7553]

Great video & tuition .... but .... what is the best way to set the engine rpm if your bike doesn't have an rpm gauge ?

[@bryencass8260]

I'm sorry if already asked and answered but where can I find this type of carb sync tool? The one with the gauges and valves not the fancy wrench

[@Zer0_Cool69]

That was really informative thanks

[@dadyo63]

Awsum vid mate,easy to follow,your gang valve is that from a fish tank air system,just wondering were you got yours,try to knock something up over here in new zealand to tune my 750.thanks muz

[@Common-motor]

I believe a fish tank valve would do the same thing for you Murray!

[@alextrapppainter]

I'm looking at buying a 350f that won't start. Do you happen to have your sink like kit for sale? That would be so much better than trying to put it together from random places...

[@geoffballe8766]

Excellent

[@Elitefrr]

amazing work. thanks!

[@FranciscoGalicia]

Awesome two videos. Thanks. So to sync it is only that? What about the air screw ? I have a Kawasaki 1978 KZ650. Thanks. Great video

[@Common-motor]

Hey Francisco, that will be it for synching! You will still want to go through and tune your idle air mixture screws and run the bike. Once synced is a good time to run the bike to check the running condition and performance. If you made any changes from stock if everything else is tuned appropriately its a good time to check your jetting.

[@FranciscoGalicia]

@@Common-motor thanks so much

[@jhoodied4861]

Syncing it with a manometer is better or worse than with these gauges?

[@JMVENTURES1523]

I really need your opinion on this. The manual for my 78 750 Four K says the idle is 850-950. I could never get the idle down that low and all my carbs are sync but not at the “green” area on the gauge. What am I missing here

[@beausbargarage6213]

Where do I get these brass tubes for the vacuums lines ? Mine is a 78. I don’t see any vacuum connections anywhere

[@daveco1270]

Interesting technique using one gauge with that four way splitter. Is that piece sold separately? I've been using a CarbTune Pro on my CB750.

[@preez77]

Interesting is the right word. You’re far better off with carbtune.

[@Common-motor]

If that’s the only piece you’re needing you can message our support and we can get you just the splitter!

[@salmanz8]

Stay with carbtune. Great video, but why overcomplicate a pretty straight forward sync process with all that extra plumbing and one guage. If you can afford all that setup, you can afford three extra guages instead. Lol Just my opinion

[@salmanz8]

Plus with the rpm changes in between, etc etc Too many variables to have discrepancies. Use a carbtune or similar all 4 at the same time setup, and i have been doing this a while.

[@mikegermain7033]

Excellent video I'm close to doing carb sync where does one aquire the single gauge set up?

[@Common-motor]

Link in the description!

[@jaredelmore1]

Can you do a vacuum sync on a two carb cb 450 twin Honda 1970.?

[@rickrodrigues2219]

So what was finally the vacuum reading of this bike at normal idle & was it stable/steady?

[@seanmckinnon6649]

Thanks informative

[@tjj6583]

Thanks for the video. Question, my 78 cb550k3 pd46c carbs rebuild idles good but when I rev up the engine the rpm stay high or is slow to return to idle. This carb butterflies are always open. They only close if I pull the choke. No vacuum leaks. Stock jets size, 2.5 screw out and second needle position. I believe this is factory setup. Any ideas? If the mixture screw is below 2 turns it wont start. Spark it good. At this time the carbs are only bench synced.

[@Common-motor]

Sounds like you need to vacuum sync. Hanging idle is one of the symptoms you will notice without it.

[@robbenalfans5501]

I have sync my carbs they function good in begin rpm 1200, the gas stop 5000 rpm, dont understand why

[@reioXyhi]

I cant see the point to not use 4 separete vacuum meters with adjusting "zero-screws" More eays to use too. Tell me where I am wrong if I am👍

[@Peter-nu6ix]

No two {inexpensive} vacuum gauges will give the same progressive and total readings. Sure it can be done as you describe, with a separate gauge off each carb. This method is obviously used by many and does, in most cases, give a reasonably satisfactory setting and tune of the carburetors. However, the single vacuum gauge will give the same vacuum readouts for each of the carbs and, therefore, be more accurate. The cost of adding four gauges to a kit for sale, instead of one, will also increase the total cost of the kit, whether purchased as a kit, or made up from individual components by the DIY carb tuner. Personally, for the sake of accuracy, I would use the single vacuum gauge and five or six valve gang of "Aquarium Air Flow Distributors with Controller Valves", using one of the valves for the vacuum release, instead of findling with a plastic cap to remove and replace {and lose}.

[@stephenrichard487]

Can anyone help me find a place where I can buy the sync tool used to loosen the lock nuts and adjust the vacuum screws? thanks

[@musimir1883]

Hello! I have a Honda CBX 1986 650E RC13 50 horses, I cannot find any difference from mine to the CBX650E 1986 RC13 75 horse one.....can you help me? What do I need to upgrade to get to the 75 horse?

[@asborgeirssoneiriksson9053]

Hi there, If you're still interested: to upgrade the CBX650 to 75hp, you'll need to change to a bigger camshaft and change ignition timing.

[@musimir1883]

@@asborgeirssoneiriksson9053 Thank you! I'm in the process of a rebuilt....of a rebuilt. Rebuilt the engine once and after 300km it starte ticking/knok.....

[@jonzissis205]

Didnt get why it makes a real difference using the vacuum sync with one gage instead of 4 paralel. Each gage checks each carb at a time. So what's the difference?

[@preez77]

CMC claims there too much variation between the gages in the 4 gage setup. Many if not most people will disagree with that.

[@Common-motor]

We’ve had gauge clusters burn us in the past and find this way it’s always foolproof with the least variables is all! At the end of the day though if you get those carbs dialed in beautifully with the gauge setup you’re using then it’s a winner.

[@tomopope4019]

@@Common-motor i bought this inexpensive gauges, similar that you got. I checked their precision to each other with one easy method. I bought a cheap hospital injection without a needle, and connected it to each gauge. Then i checked every gauge by itself (I pulled the injection all the way from bottom to top so every time you vaccum the same ammount of a air ). All the gaugea showed almost same result. Another methode to check you gauges is with brake bleeder pump. What do you think about this?

[@preez77]

@@tomopope4019 what you did is a good way of checking the gauges. You could also use a 4 way splitter and a brake bleeder pump to calibrate all 4 gauges at same time. At the end you will find out they are pretty close to each other.

[@DADSGETNDOWN]

Didn't clear the guage when going from 4 back to 2.

[@ryanmg02]

I have a 86 Kawasaki Eliminator zl900 will this kit work? It only says Honda on the website?

[@Common-motor]

It’s going to come down to whether or not the vacuum sync ports are the same thread. Message our support at common-motor.com with what thread your zl900 uses and we can confirm for you

[@oakcreeklombard6311]

When you start a cold bike how long do you leave the choke on for?

[@imperialdelmejor8186]

Till the gas begins to response faster

[@davidbisnette7673]

How do you make one of those sync tools

[@Common-motor]

We sell the whole kit on our site ready to go!

[@Trendsfreak]

Why would you fiddle with one dial and make it so complicated, just buy yourself a carbtune synchronisation kit and you can monitor all four carbs at once very easily.

[@Common-motor]

We find this to be the easiest and most accurate method to teach and use but there are many ways to do it. The Morgan Carbtune is a great device and can do the job as well.

[@nicolascorredor449]

Poner subtitulos al español por favor gracias

[@wilfredprins9718]

Small question Which engine oil you recommend for a 1973 350F

[@supersportimpalass]

10w40 is stock recommended but can go with 20w50 if you ride in a hotter climate. I use Amsoil metric synthetic in my CB550 without any issues but some people fear using synthetic in older engines for whatever reason. A good deal of people use regular Shell Rotella diesel oil. Any motorcycle oil designed for a wet clutch will work. Just personal preference.

[@wilfredprins9718]

@@supersportimpalass im in the Netherlands, not that hot. Thanks for the reply

[@supersportimpalass]

@@wilfredprins9718 You're welcome. Motul has their 3000 4T 10W40 mineral oil which I believe is available to you. www.motul.com/nl/en/products/3000-4t-10w40--2

[@gerberfx]

PD carbs are a nightmare, the worst carbs from any CB Four

[@rabbit3502]

👍

[@benderbender1233]

🤘😎

[@glennmerriman8382]

I cannot see the need to zero the gauge each time you swap cylinders. Seems rather pointless.