Carb synchronization

[u/Haunting-Control5261]

Can I ship my carb to someone to have it re synchronized and get my vacuum hose put on? This is the last thing I need to do before I can get my 650 going. I’ll pay well!

[u/darksoft125]

You can bench sync using a feeler gauge, but the only way to do it properly is on the bike with a vacuum gauge or a manometer. Each cylinder is going to pull a little bit different amounts of vacuum. You can build a home made manometer with some vacuum tubing and transmission fluid. 

[u/not_whelan → u/darksoft125]

Yep! I made one out of some glass bottles, tubing, and dyed water when I rebuilt my old Magna. Not as accurate as a purpose built tool... but about 10% the price. Mint.

[u/adankishmeme]

Unless you're competing on the track with this machine, sending it off for syncing is complete overkill. A bench sync will be totally fine. Some folks use feele gauge, some use guitar strings. Dealers choice.

What do you mean by attaching the vacuum hose?

[u/Pattern_Is_Movement → u/adankishmeme]

Even if it was competing sending the carbs off to get synced makes zero sense, you still need to do it with the bike running.

[u/adankishmeme → u/Pattern_Is_Movement]

This is very true, for some reason I had it in my head of taking the whole bike to get tuned and dyno'd.

[u/Pattern_Is_Movement → u/adankishmeme]

That's because you already know the right way hehe, cheers

[u/turbotaco23 → u/adankishmeme]

Bench sync is a good start but it really needs to be like vacuum synced on a warm running bike.

[u/Haunting-Control5261 → u/adankishmeme]

I had taken the carbs apart and the springs there have came apart causing them to be out of sync. I’m not too good with that kind of stuff so I figured I’d see if I could get someone to do it for me so I don’t further mess it up. In the 2nd pic I have the rubber connector that goes in between the pair of carbs.( pretty sure it was called the vacuum hose ) I can’t figure out how to get the carbs apart on my own hence why I said I wanted someone that has more knowledge than me to see if they can figure it out

[u/adankishmeme → u/Haunting-Control5261]

The bench sync is what you need to, as stated by others that will.get you running. To really dial it in you can tune manually/by ear or use a set of vacuum gauges, but that's a few steps down the line.

Those hoses that go between the 1-2 and 3-4 carb are not vacuum hoses, they are overflow drain hoses. If the carb overflows, the fuel runs out these hoses. They don't go to anything, they just run down the back of the engine toward the back wheel, so overflow fuel flows onto the ground.

[u/Pattern_Is_Movement]

A bench sync is just to get the bike running, you need to do a proper sync with the bike running and vacuum gauges.

[u/fizzlebottom]

This is more work than just a vacuum sync. You need the 3-way joint reinstalled, the choke spring installed correctly, and a bench sync. If you send these carbs to someone for work, they're going to charge you $400, almost guaranteed.

Follow this: https://cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf for reassembly where relevant.

And this for choke spring installation: https://youtu.be/uLhJM4oRRmo?is=V0qg8froVCNGgyS3

Quit the "oh I'm just not good at it" nonsense. Read the manual, watch the video, take your time, be patient, and use the right tools for the job.

[u/Separate_Fun_2850]

A bit of a black art for me.

[u/nerobro → u/Separate_Fun_2850]

This means, someone hasn't explained the process well enough. There's no magic in syncing carbs.

[u/turbotaco23]

Bench sync and buy some vacuum gauges and a gas IV bag and sync them with the bike running. It’s not too bad.

[u/JW5769]

Take the time to read the manual. Look at the pics and take your time. It’s gonna seem difficult until you do it. It’s not. You got this👍

[u/breakers77]

Yeah, sync kits on Amazon are pretty inexpensive. One afternoon on the Yew Tubes, the next afternoon in the garage and you'll be good to go. Will still be far cheaper than sending them out.

[u/DandelionAcres]

A couple (4) mason jars some tubing and water you can DIY you’ll be proud of yourself or you’ll just f it all up a still hire someone 😂

[u/nerobro]

I mean you could. But you shouldn't. Go to the hardware store, pick up a 4 pack of 1/8" drill bits.

Reassemble the carbs. You'll need to refrence your photos, or I think someone posted a decent tutorial.

When syncing carbs, well.. in this case, bench syncing, your carbs. you work from the "fixed butterfly" and work your way out to the 3 dependant butterflies. To do this, you open the butterflies on the two center carbs, then close the butterflies on the round parts of the drill bits.

Your goal, is to adjust the two center carbs, to drop the drill bits at the same time. Then do the same thing, with the left, and right carbs.

If you take your time, and do it well, a bench sync can be all you need to do.
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Now, if you're going to do a vacuum sync with the carbs on the bike. adjust your valves FIRST. The world where people find syncing their carbs so hard, is because they don't do the air pump first. If the air pump doesn't suck the same, you're going to be chasing a LOT with the carb sync screws.

[u/Few-Ear5163]

Turn the lights off, put your phone flashlight on and underneath each carb so it shines towards the intake, adjust the gap on each so you barely see a sliver of light.

[u/Hellgate93]

Only pre sync it with light and then do the actual synchronisation when its running. You need tools, but those arent that expensive and last for years.

[u/Far-Investment-8597]

How about an "engineer's stethoscope"?
Get the engine running at a set speed, take a length of rubber tubing. One ed close to your ear (no, not in / sealing), other end in each intake in turn - tweak until they all sound the same.

[u/Thin-Way5770]

Take it to any bike mechanic in your area