Topic: 1972 CB500 Carb Setting Questions

[jmelche2]

1.) I need to know the proper method to bench sync the carburetors.

2.) With the choke in the open position, cylinder 1 is fully open while 2, 3 and four each closed slightly more than the previous.  In other words, four is closed slightly more than three, three mose than 2.  I'm not sure how they got this way but assume they should all be adjusted to full open. 

Thanks, Jim

[Deltarider]

Assuming you mean the choke-flaps (they're not for syncing of course) I guess it is normal after having seen the same on two sets of CB500 carbs: my own and somebody else's. See pic. Or is yours the other way around?

[jmelche2]

Your picture demonstrates the progressive closing of the choke plates I was referring to.  There is an adjustment for this but I wanted to check with others before I mess with it. 

I also want to bench sync before I reinstall so waiting on advice as to how to do this.  I read that #2 is non-adjustable but I see an adjustment for each cylinder.  Are the adjustment screws the four vertical screws with the lock nut?   

[Deltarider]

Your picture demonstrates the progressive closing of the choke plates I was referring to.  There is an adjustment for this but I wanted to check with others before I mess with it.

I wouldn't mess with them. Maybe, maybe it has to do with the asymmetric position of the 4 throats towards the plenum. Maybe.

I also want to bench sync before I reinstall so waiting on advice as to how to do this.  I read that #2 is non-adjustable but I see an adjustment for each cylinder.  Are the adjustment screws the four vertical screws with the lock nut?

What makes you think you have to sync? Mine didn't need it in tens of thousands of kms.
If you must, start by consulting the correct manual for the 500. The old style Kei-hins like on yours are all 4 adjustable, in other words they don't have a mothercarb. There was a pic posted recently. Let me see if I can find it. Ah, here they are, the smaller are for adjustment but again: sure you have to sync? Honda made it so it doesn't need adjustment, not unless something else has changed. I had my own way of benchsyncing, but somebody posted a method with ball bearings and I thought it was convincing.

[Sprocket75]

I used the 1/8" drill bit method. I also tried the light method suggested by TwoTired. I used a super bright LED and a piece of black construction paper. I think the drill bit method was easiest. Either way, after taking my time and carefully bench syncing them, very little adjustment was needed once I mounted them back on the bike. The vacuum gauges confirmed that I was VERY accurate. A few minor tweaks with the carb tool, and she runs silky smooth now. I started with #2...set it, locked it down...then #3...then #4...then #1. I don't think it really makes a difference though. One thing to note though, give yourself plenty of room for the idle adjustment screw. I didn't understand this when I first read it, but after watching it on the bench, I began to see what they were trying to tell me. I have been thinking about posting a video of the process in detail. Seems like it might be helpful, but then again the info is on this forum numerous times. Sometimes it helps to watch a process though rather than read it.

[jmelche2]

One thing to note though, give yourself plenty of room for the idle adjustment screw. I didn't understand this when I first read it

Okay, I don't understand it either.  Can you please explain?  Thanks, Jim

[Scott S]

 In the picture of the choke butterfly's that Deltarider posted, there are three screws between the carb bodies/throats. By adjusting those screws, you can raise or lower the choke butterfly's and make them even.

 In the second pic he posted, those small screws with lock-nuts on them, connected with a band of metal, are your synch screws.

 Mark the current position of your idle adjustment screw. Just use a Sharpy and make a dot or dash or something on the knob. Now, turn in the knob say, half a turn. You should see the slides of the carbs start to rise. Do this until you get the LOWEST of the four slides high enough to slip the smooth end of a 1/8" drill bit under. Use it like a feeler gauge; just a tiny bit of drag. Be sure to count the turns of the idle screw that it took you to get  there.

 Once the highest slide is set, use those screws/locknuts to adjust the other three slides to match, using the drill bit. Once they're even, lower the slides using the idle knob, going back however many turns you went in. This should get you close enough to crank the bike without having the idle race to 4 or 5K.

 Be sure to set the idle mixture screws to the factory settings, usually 1.5 turns out, but check ffor your particular model.
 If you cleaned these carbs, make sure you removed and cleaned the emulsion tubes. If you used an aftermarket jet kit, keep and re-use the factory Keihin pilot jets (heck, use all the factory jets, unless you're upping the mains for some reason). If you cleaned the carbs and think they're clean....go ahead and clean them one more time before installing. Trust me.

[Deltarider]

In the picture of the choke butterfly's that Deltarider posted, there are three screws between the carb bodies/throats. By adjusting those screws, you can raise or lower the choke butterfly's and make them even.

Well, if you must... but please, read what I posted before. Yours are not an exception. In fact yours show the same phenomenon as found on others including mine.

[lucky]

Syncing the carbs means the throttle slides,not the choke butterflies.
Leave the choke plates alone.

When you bench sync the throttle slides you are just trying to get all 4 of them to open or close at the same time. Thats it.

You can use nothing, a drill bit, a piece of anything, but you can also just pull the throttle and put you finger on the slide to feel the slide start to move as soon as you start to pull the throttle.

When you use a vacuum gauge it gets the slides so that the vacuum is the same based on different inconsistancies and .007 thousands of an inch can make a difference.

You may notice that when you vacuum sync the carbs that 2 of them are close and the other two are off. That is caused by linkages between carbs having slop in them.
Air leaks etc.,.

[lucky]

1.) I need to know the proper method to bench sync the carburetors.

2.) With the choke in the open position, cylinder 1 is fully open while 2, 3 and four each closed slightly more than the previous.  In other words, four is closed slightly more than three, three mose than 2.  I'm not sure how they got this way but assume they should all be adjusted to full open. 

Thanks, Jim

Buy a workshop manual and read it.

Pretend it is an I pad or phone. LOL..lol

[Sprocket75]

Will this help?

[Deltarider]

I used to do it from the other side with a small allen key. Now, the ball bearing method appeals most, I must say.

[jmelche2]

Wow, what a great source of information!  Thanks guys for your help. 

[Sprocket75]

Well??? Did you sync them??

[jmelche2]

Yes.  Bench sync carbs, set needle jets to third position and idle mixture screws to one turn.  Took the bike for a quick two mile ride and it is running great.  Thanks again for all the advice!

Jim