Topic: Ball Bearing Carb Bench Sync (PD Carbs)

[DustyRags]

Copper wire's too dense- those seals are asbestos wrapped in a thin copper tube.

My brother's had great success with loops of rolled-up tinfoil in his Nighthawk, though

[Deltarider]

Brewski, your method works. Actually it's an old method. Here's some advice for all newbies that after reading all the above can't wait to start syncing: do not hurry.
Early 80s I bought a synchronisation set of 4 manometers together with a friend. He moved to one of the islands. In the last 20 years I've benchsynched my carbs only 2 or 3 times and I did well within 2cm HG. So it can be done. This summer the friend contacted me about the vac. set in his garage. He had become a Yamaha one-cilinder convert and he didn't need the set anymore. Neither do I, I replied but I'll come by to pick it up anyway to make somebody else happy. Here's why. A friend of mine, a mechanic (marine diesel) decided he wanted an old SOHC four and had chosen an old CB350Four, because from a mechanic's point of view that's the model he admired most. I've helped him adjust the camchain tensioner, lent him my coils to spot a faulty condenser (!) and helped him with the documentation. Last time I was around he had the rack of carbs on his bench.
I made him clear all maintenance can be done by just opening the float chambers. No need to remove the top lids, nor to separate the carbs. He was pleased to welcome the vac. set in his workshop. When I noticed the yellow loctite was still on the little adjusters of his carbs, I made him promise NOT to start syncing. "I guarantee you, they're allright, just don't touch the adjusters" and I told him about the synchronize-and-floattang-bending hysteria in this forum.
Ofcourse reading vacuum can be usefull to detect if something is wrong (valves or whatever). But, don't believe Honda SOHC Four carbs go out of sync by them self. They don't, with the exception of the first cableoperated carbs found on the first 750s. Honda learned well from these first 750 carbs and designed a very reliable shaft operated system. I know the manual mentions to check synchronisation every so and so many kms. If you detect differences there's something wrong in the engine, not with the carbs or the carb adjusters, unless somebody else, who had not been able to read my advice, has 'toyed' with them. That's what I wanted to say. Thank you very much (sigh).

 

[750resurrection]

Copper wire's too dense- those seals are asbestos wrapped in a thin copper tube.

My brother's had great success with loops of rolled-up tinfoil in his Nighthawk, though

 I'm sayin dude I ******* out and they cost $20 bucks for 4.

 The other place has another set on order, so it's going to be $40 when idiot is done.

 Frikk - shoulda used bubble gum wrappers, a better design than the Hondagineers have there.

 Speaking of that, it's been a long time - does the black mark on the oem copper ex rings go up or down ? (ask frikkin Honda why...)

 AND... do the flapovers around the ring (seam line circling one side of the rings) go in toward engine or out toward pipes ?

[brewsky]

Delta,

Thanks for your comments, and I also believe in the theory "if it's not broke, don't fix it".

I don't know how old the ball bearing method is, but I have seen it mentioned several times, but not discussed on the forum......at least that I could find.

I do think bench or vac sync it is called for if the carbs have been apart, or even the needle height changed, as part of the linkage has to be dis-assembled to do so.

The ball bearing method just seemed so much easier and more precise to me than my previous bench methods.

It doesn't really matter how precise the bench sync is if you are going to vac sync anyway. But, if you don't have a access to a sync outfit, I highly recommend it.

[phil71]

That is certainly the most precise way to do an imprecise thing..

[andrewk]

Ofcourse reading vacuum can be usefull to detect if something is wrong (valves or whatever). But, don't believe Honda SOHC Four carbs go out of sync by them self. They don't, with the exception of the first cableoperated carbs found on the first 750s.

That's not true at all.  The sync will change with engine wear- it's not something you "set and forget."  As volumetric efficiency in the engine changes (wear in the bores, wear on the valve seats, wear on the cam), so will the carb sync.

I can't tell you how many carb racks I've seen with the loctite still intact that were out of spec.

[brewsky]

That is certainly the most precise way to do an imprecise thing..

Thanks for the comments, but they just make no sense to me.
Care to explain why?

[Killer Canary]

I doubt that the trauma of prying the carbs off the bike in the first place is good for the sync.

[Bailgang]

Ofcourse reading vacuum can be usefull to detect if something is wrong (valves or whatever). But, don't believe Honda SOHC Four carbs go out of sync by them self. They don't, with the exception of the first cableoperated carbs found on the first 750s.

That's not true at all.  The sync will change with engine wear- it's not something you "set and forget."  As volumetric efficiency in the engine changes (wear in the bores, wear on the valve seats, wear on the cam), so will the carb sync.

I can't tell you how many carb racks I've seen with the loctite still intact that were out of spec.

I think what he's trying to say is that it's not the carbs themselves that go out of sync all by themselves but engine wear as you stated that cause the carbs to go out of sync. I imagine if an engine were able to maintain it's volumetric efficiency without change then it's reasonable to think the carb sync wouldn't change either. However that's not going to happen because engine wear of some degree will occur which will in turn affect the sync.

[Deltarider]

I think what he's trying to say is that it's not the carbs themselves that go out of sync all by themselves but engine wear as you stated that cause the carbs to go out of sync. I imagine if an engine were able to maintain it's volumetric efficiency without change then it's reasonable to think the carb sync wouldn't change either. However that's not going to happen because engine wear of some degree will occur which will in turn affect the sync.

Yep, that's what I ment. As a racer once told me: you're powdering a rotten engine.
Reason I wrote my previous post: I've seen many bikes introduced here in an almost virginal state with very few miles indeed. I'd hate to see newbies start syncing because they read so much about it here. My bike had it's first synchronisation check at odometer 52000 KM. And that was only - no shame to confess it - because I just liked to play with a new set of manometers...
 

[750resurrection]

 So once again the manual and maintenance schedule is wrong... ? lol

 If you have any buzzy bars, a bad idle, sync your carbs. Most of us aren't lucky enough to find the no lemon juice at all 30+ year old Honda that hangs tight for half a 100k, or bought it brand new and have it for 52k miles run, then be a noob, too.

 Congratulations on your highly unusual super duper.

 If you happen across a low mile pristine bike, you still have the PO who knows what, then the never not a problem carbs, and the possibility of any amount of 30+ years gas crap in those carbs, drained, undrained, recently drained, stored with now dry rotted idle screw rubber gaskets that leak, on and on...

[Deltarider]

You don't get it. If you're carbs are untouched, you can find your nice idle by adressing all other maintenance items, like ignition, valve clearance, ignition, camchain tensioner, ignition. Oh, did I mention ignition? If you cannot find back that nice idle, there's something wrong in the engine. Using a vac. set then is a good way to spot where the trouble is.
Notice the difference in approach?

[750resurrection]

 No I certainly do get it, and did get it. Perhaps you don't get it. There are I or we if I'm not the only one that runs what they have - and thus, the vac is not the same across all the cylinders.
 No matter, no point anyway, if the engine gets addressed, then the carbs needs synced anyway.

 Not like you're going to reproduce exact factory vac on all 4, especially after any mileage, rebuild, valve adjust, etc. It just ain't happening.

 I'm sorry, like I said, you're very lucky, your perfect world engine is awesome.

[andrewk]

You don't get it. If you're carbs are untouched, you can find your nice idle by adressing all other maintenance items, like ignition, valve clearance, ignition, camchain tensioner, ignition. Oh, did I mention ignition? If you cannot find back that nice idle, there's something wrong in the engine. Using a vac. set then is a good way to spot where the trouble is.
Notice the difference in approach?

I agree that synchronization is the last step in the tuning process, but I don't know under what conditions you'd find a set of carbs that couldn't use some fine tuning.  Even "untouched" carbs will have wear in the linkage, and wear on the slide that make the sync drift.  You talk about it like it's some method of last resort- why wouldn't you want the engine to run its best?  Set all the other stuff first, and then check the sync- 90 percent of the time it's going to need adjustment, or adjustment will make the bike run better.

[phil71]

I know this has been covered about 6 times here, but whatever.... this is a beaten dead horse anyway. You wanted to know what i meant about being a precise way to do an imprecise thing: bench sync is just to get the linkage on straight till you get the carbs on and the bike running. The chances that the motor EVER had the same volumetric efficiency across 4 cylinders is about a zillion to one...then you put thousands of miles on it... and it strays even more. So, the reason you vacuum sync at all is to compensate for differences in voumetric efficiency. In other words, any extra time you spend making the physical sync measure up is time you'd have better spent doing a vacuum sync.

[brewsky]

I know this has been covered about 6 times here, but whatever.... this is a beaten dead horse anyway. You wanted to know what i meant about being a precise way to do an imprecise thing: bench sync is just to get the linkage on straight till you get the carbs on and the bike running. The chances that the motor EVER had the same volumetric efficiency across 4 cylinders is about a zillion to one...then you put thousands of miles on it... and it strays even more. So, the reason you vacuum sync at all is to compensate for differences in voumetric efficiency. In other words, any extra time you spend making the physical sync measure up is time you'd have better spent doing a vacuum sync.

Thanks for explaining what your statement. We have basic agreement on the theory, just a different take on the application.

The title is about how to do a "bench sync" and some are trying to make it into something different. I've found the ball bearing method is the best, most precise and easiest way to do that. Many people don't have access to vacuum gauges or sticks, and if not, I believe a precise bench sync is very beneficial. I also believe that if you do a precise bench sync, you will lessen the chance of needing to do adjustments during a vacuum sync.

The purpose of a "bench sync" is to get the carbs as close to the "as designed" state as possible. If you start a vacuum sync there, there should be less adjustment necessary than if starting from some random slide settings.

And you MAY find there are no further adjustments necessary to have the vacuum readings within factory tolerance.

To me, if you are going to do a vacuum sync anyway, you don't NEED to be precise with a bench sync, but it just makes further adjustments easier.

Another benefit of starting a vacuum sync from a well bench sync'd state, is that if you do have any significant difference in levels, you will know it is more likely the result of potential engine issues, rather than sloppy slide position settings.

[lrutt]

You are completely off course on this whole thing. WOW.

This method of ball bearing, drill bits, or anything else is not going to work.
The idle will be sky high.
.007 will actually make a difference. 1/4(.250 thousandths) Insane!

The slides all need to be down all the way. And the opening that is left is correct.
These carbs are not like the earlier carbs.

Nowhere in the manual does it mention sticking ANYTHING under the slides!
Matter of fact there should be free play in the throttle cable and the slides should all be bottomed out. When they are bottomed out you well see a crack of opening.

You can always raise the slide later.
WHEN YOU SYNC the carbs IT IS RAISING OR LOWERING THE SLIDE!!!
Keep the idle as low as possible. Start with #2 carb.

wow, so for the last 40 + years I've been working on multi carb bikes, using 1/16" drill bits instead of ball bearings I've been doing this all wrong. Amazing. And even more so that it has worked so effectively, to the point that I rarely have to re-adjust when I put the gauges on.

I feel so inadequate now. Guess I need to go out and redo all my bikes

[Killer Canary]

Ball bearing synch is the only method I can use on the 350 twin; no vacuum ports and 2 into 1 exhaust.

[750resurrection]

 I've never done a ball bearing bench sync, but that's what I will try next time, because the drill bit method is difficult, aligning the bit straight, making certain it's flat against the air inlet tube, and then having it centered.
 
 I had a hard time and was checking and rechecking and going over and over it. ( I can see where some practiced skill would make this easier).

 With a ball bearing sync gravity would do all that aligning for me.

 My bike is so hacked together the home made vacuum sync helped a great deal.

 I will say Delta does have a point because a good condition bike may respond much better initially than mine. Brewsky gave a great explanation his last post, and I do believe they are both correct that bench sync is very likely to bring the bike within the 2mg spec. (if it's in decent shape)
 However, I believe home made manometer syncing after the bench sync is actually the way to go, as it's sensitivity is refined, and I believe the results will speak that truth even on a good condition engine.

[brewsky]

You are completely off course on this whole thing. WOW.

This method of ball bearing, drill bits, or anything else is not going to work.
The idle will be sky high.
.007 will actually make a difference. 1/4(.250 thousandths) Insane!

The slides all need to be down all the way. And the opening that is left is correct.
These carbs are not like the earlier carbs.

Nowhere in the manual does it mention sticking ANYTHING under the slides!
Matter of fact there should be free play in the throttle cable and the slides should all be bottomed out. When they are bottomed out you well see a crack of opening.

You can always raise the slide later.
WHEN YOU SYNC the carbs IT IS RAISING OR LOWERING THE SLIDE!!!
Keep the idle as low as possible. Start with #2 carb.

wow, so for the last 40 + years I've been working on multi carb bikes, using 1/16" drill bits instead of ball bearings I've been doing this all wrong. Amazing. And even more so that it has worked so effectively, to the point that I rarely have to re-adjust when I put the gauges on.

I feel so inadequate now. Guess I need to go out and redo all my bikes

I used drill bits, touchy-feely, see the light, and probably some more techniques I've forgotten over the last 40+ years also, and my bikes ran well, idled well, and picked up off throttle well without any vac sync at all.

Not to say they wouldn't have been a little smoother with the vac, I just didn't have one to use and didn't feel the need to buy one.

I just happened to hear about this method on this forum, decided to try it, liked it, and decided to share it since I hadn't seen it discussed in detail before.

However, if you really still feel inadequate, and if it will lighten your re-do load, I will be happy to take the Hustler off your hands!!



 

[Deltarider]

 

I will say Delta does have a point because a good condition bike may respond much better initially than mine. Brewsky gave a great explanation his last post, and I do believe they are both correct that bench sync is very likely to bring the bike within the 2mg spec. (if it's in decent shape)
 However, I believe home made manometer syncing after the bench sync is actually the way to go, as it's sensitivity is refined, and I believe the results will speak that truth even on a good condition engine.

I specifically adressed newbies and expressed my concern for the bikes that are almost still in a virginal state. Can't believe how little miles some have done. Yes, I've been lucky I still have the bike I bought april 1979 and I realise that makes it easy for me to speak. But... somehow I have this feeling that a lot of you synchronizers are adressing the 'effort' the PO has done. That's my point and you'll be a PO too. The same goes for this floattangbending. There's this echoing, which is a serious internet disease. I frequent the German and French SOHC site. I can't remember I've ever read about adjusting floats there. Makes you think.

[aperry]

Just want to comment that it seems like a large percentage of projects on this forum are cafe or other non-stock builds in which it's extremely common to replace the stock airbox.  Pods and velocity stacks require re-jetting and changing the needle clip position.  On my 750 this requires that you remove the slide adjuster lock nut.  I would imagine many other CB's are the same way.  Anyway, often this is out of necessity because you've made the decision to remove the eyesore, I mean, the airbox.  (and may live to regret it)

[750resurrection]

 Delta, okay. Let's say whatever - lol - whatever that means.

 If anyone has done a bench sync then found no adjustment needed on a manometer sync, please speak up, maybe add engine condition or whatever you may have done there.
 
 Inkscars is not a noob and a long time member like you, but she just recently threw out your attitude on the matter, and came in kicking herself for her three years of being stubborn and not syncing.
 Doesn't matter was the jist, a real good tuned bike, etc.
 She changed her mind.
 Inspired me, very glad she did.

 So although float tang bending might be overblown, a lot of members here go for as close to perfection as possible it appears, and it looks to me many bring back wrecks with that method - so okay, might be some misunderstanding with that aspect, float tangs could be important with mixing and matching new and used carb parts and mailing the floats around etc. ( which is why you said pristine low miles concerning syncing... okay)
 
 I've also seen a few engines in my life that were not lemons at all. They just ran forever without work. Saw one go over 300k and passed emission inspection, it must have had good engine metal and sweet tolerances by chance, it never missed a beat, even with no engine rebuild work.

 So yeah exceptions, I've seen them in car engines, certainly some occur in bikes as well, especially with the production numbers of these, increasing chances for that.

 Okay enough of my blabbing.  I'm a true believer 100% in carb syncing these 4 cyl hondas, and I say use a home made liquid tube job which is highly sensitive - you get that puppy good, you've got a very nice tune.

[brewsky]

 If anyone has done a bench sync then found no adjustment needed on a manometer sync, please speak up, maybe add engine condition or whatever you may have done there.
 
 

Just did, as indicated earlier in this thread.
23,000 miles
stock engine
stock 4/4 pipes (end baffles cut out by PO)
UNI foam filter in orig airbox (top removed)
valves adjusted, points cleaned and re-set, cam chain adjusted, timing set with timing light

The bench sync resulted in 0.8" HG max difference on a Motion Pro mercury manometer. That is 1/2 the allowable tolerance stated for the 750's of 1.6" HG

It may just be luck and a one time event. Just have to wait till next time to see if it is repeatable.

However, just as you say, when you use a DIY oil manometer, the differences are greatly magnified, and there was a 9" difference (oil level) when I hooked my own DIY unit up. I was only able to get that down to 6" with my patience level. I'll probably try to get closer next time.

Of course, which type manometer you have dictates how close you can adjust.

[750resurrection]

 Okay my fault sorry I missed that earlier in the thread, your post is instructive, thanks.