Topic: Ball Bearing Carb Bench Sync (PD Carbs)

[brewsky]

Did a search and didn't find this subject discussed, so thought I'd post this.

Till recently, I've been using the "watch for the first light", or "drill bit" methods to bench sync, but they left me wondering how close they really were afterwards. The drill bits seem to move around a little bit, and the light method left me wondering if my eyes were really at the same angle for all carbs.

So here is my curent method:

1. Find 4-¼ inch ball bearings (old steering stem bearings work perfect)

2. Loosen the adjustment lock nuts on carbs 1, 3, & 4, and turn screws to roughly equalize the slides at rest.

3. Place carbs on bench engine side down

4. Place one ball bearing in the intake throat of carb #2

5. Begin opening the throttle by turning the idle adjustment screw slowly

6. Watch for the instant the ball bearing falls thru the slide and immediately stop turning the adjustment screw

7. Place a ball bearing in carb #1 and slowly turn the slide adjustment screw until the ball bearing just falls through. Tighten the lock nut.*

8. Repeat for carbs 3 & 4

9. All 4 carbs should now be in bench sync.

10. Test by closing the slides slightly, and placing a ball bearing in all of the carbs

11. Now open the throttle slowly with the idle adjustment screw and watch for the first ball bearing to drop. If one drops, and others remain, re-adjust till they all fall at the same time.

*Keeping the lock nut partially torqued while adjusting the screw will lessen the chance of the clearance changing when the nut is tightened.

Don't really know if this is any better than the other methods or not, but at least it "feels" better

Now to test the results with a borrowed set of mercury sticks!

Will post the results.

[brewsky]

Adjustment screws:

[aperry]

That's a pretty cool approach.  I'm interested to know how close you've landed once you fire it up with the vacuum gauges. 

I'm currently running with bench synced carbs (drill bit method).  My mercury carb gauges (borrowed) give me fits and every time I try to fine tune the carbs I somehow end up making them worse.  I've read through tons of approaches that people have authored here.  Anyway, according to the gauges I'm pretty close right now and the bike feels great.  Good enough for me.

Subscribed.

[70CB750]

I like it.

[TwoTired]

Mechanical sync does not equal vacuum sync.  ...unless all four cylinders have the exact same efficiency, meaning all the cam lobes have perfect profile, tappet clearance perfect, valve seal is perfect, piston seal perfect, etc.
I remember my statistics instructor explaining that only the angels deal in perfection, us humans can only get close.

The ball bearing/drill bit methods are nearly equal in effectiveness.  But, it is not recommended for carb models where ALL four positions have an adjuster.  These methods ignore the necessity for ensuring that all the carb slides can reach the floor of travel, so that the idle knob has full control of slide opening position.  The PD carbs circumvent this, by not providing an adjuster on #2 carb position.

Individual creativity rating- 10
Universal application rating- 2

Cheers,

[lucky]

 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.

[aperry]

There's a lot of things that we do that are not reflected in the manual!

On my carbs (657a), I'm pretty sure the filter side of the slides is much more open than the engine side of the slides, when bottomed out.  The slide is a "crack" open on the engine side, and something like an eighth inch on the filter side.

I agree with Brewski about the drill bit method feeling a little "sloppy" due to the bit not always being centered and perfectly perpendicular to the slide.  Round ball bearings seem like a logical solution.

Aaron

[lucky]

There's a lot of things that we do that are not reflected in the manual!

On my carbs (657a), I'm pretty sure the filter side of the slides is much more open than the engine side of the slides, when bottomed out.  The slide is a "crack" open on the engine side, and something like an eighth inch on the filter side.

I agree with Brewski about the drill bit method feeling a little "sloppy" due to the bit not always being centered and perfectly perpendicular to the slide.  Round ball bearings seem like a logical solution.

Aaron

You need to go take the slide of any carb out and REALLY look at it.
The air filter side of the slide has a cutaway in it and the engine side DOES NOT.

QUOTE: " I'm pretty sure."  That says it all.

If you had really looked at it, you would know for sure.

Let the slides bottom out. Then make adjustments.
Usually the problem is getting the idle lower.

[aperry]

I think you misunderstood me. 

"Pretty sure" means, I know one side has a cutaway and I think it's the filter side, but it was months ago and I couldn't remember for sure.  More importantly, at least with my carbs, the drill bit method worked great and the reason is because you do it on the side with the cutaway where 1/8" seems to be very close to where you need to be in the adjustment range for a reasonable idle (leaves only a crack on the engine side).  This method has been documented all over this forum, including the FAQ.

I would imagine the ball bearing method would work even better because in theory it would solve some issues inherent to the drill bit method.  I don't know if 1/4" ball bearings are too big.  Since 1/8" has worked well for me, I'd probably look for that size.  But to each his own. 

[Bailgang]

The ball bearing/drill bit methods are nearly equal in effectiveness.  But, it is not recommended for carb models where ALL four positions have an adjuster.  These methods ignore the necessity for ensuring that all the carb slides can reach the floor of travel, so that the idle knob has full control of slide opening position. 
Individual creativity rating- 10
Universal application rating- 2

Cheers,

If you start by making sure all the slides reach the floor to begin with, I don't see a problem in fact that's the way I start a bench sync on my 550's 022a carbs. Once I'm satisfied that all the slides reach the floor I'll pic a carb, usually #1 or #4, lock it's syn screw down and then use a small drill bit and crack the idle speed screw until that bit can go in then gently back it off until I can feel the slide just starting to drag on the bit. At that point I'll leave the idle speed screw alone and adjust the slides of the other 3 carbs using the sync screws and adjusting the slides to the same amount of drag on the bit as I did the first carb. I agree that a vac sync is still needed but it's close enough to fire up.

Lucky you need to re-read step #5, he's starting with opening the idle speed screw. Sure the idle would be sky high if he didn't back it off when all was said and done but that's the whole point, all he'd have to do is back off the idle speed screw. It's easy peasy.

[phil71]

Ilm with Twotired, putting much energy into more precise bench synch is a waste of your time. The drill bit and light test is close enough, and not a substitute for vac sync.

[Bailgang]

Ilm with Twotired, putting much energy into more precise bench synch is a waste of your time. The drill bit and light test is close enough, and not a substitute for vac sync.

Agreed that a vac sync is still a must but I don't understand why he'd be wasting anymore time using a ball bearing. The procedure is still the same, the only diff is using a ball bearing rather than a drill bit.

[brewsky]

Ilm with Twotired, putting much energy into more precise bench synch is a waste of your time. The drill bit and light test is close enough, and not a substitute for vac sync.

Actually, I've found it takes less time and hassle than the light or drill bit method, so even if it is equal in result to either, I prefer it.

I don't contend it is as good as a vacuum sync, but if you don't have a set of gauges, or sticks, it's certainly better than "don't worry about it" IMHO.

AND......... experiencing the thrill of watching all 4 drop at exactly the same time when the throttle is opened means it's not a waste of time for me!

[brewsky]

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.

It actually does  work, and I'd venture a guess there are many others who have thousands of miles using  similar methods also.

The problem I see with being content to have all 4 bottomed out perfectly, is that doesn't take into account the slop in the linkage that doesn't show up till you reverse the forces from closing to opening.

I will test that theory, just to convince myself, however.

[aperry]

Very curious to see your initial vacuum test results (if/when you hook it up).

[brewsky]

Very curious to see your initial vacuum test results (if/when you hook it up).

Will be working on it today.......

If I remember correctly (and that is certainly questionable), last time when I checked they were within 2 adjacent marks on the sticks, which would be within 2 cm.

I also have a home made version with oil instead of mercury I haven't had a chance to try yet.

[flybox1]

I also have a home made version with oil instead of mercury I haven't had a chance to try yet.

Baby seal or virgin olive? 

nice working coming up with another method....

[Bailgang]

Very curious to see your initial vacuum test results (if/when you hook it up).

My guess probably still going to be a mile off. I use the drill bit method on all 4 slides on mine and it is a mile off on initial start up but close enough to keep from sucking oil from my DIY manometer. I understand what TT is saying about how near impossible it would be to have all 4 cyls being exactly as efficient with each other so one can argue that getting a bench sync as precise as possible is a waste of time but for me it's not that big of a deal. I figure most people would spend more time picking a stubborn booger out of their nose than the time it takes me to get all 4 slides at the same height.

[78whiteorbs]

Very creative and I like the way you think Sir~!
The fact that it is ineffective or just as good as any other is a reality but I like the way you think. I bet you are the kinda guy that makes his own tools and prolly find
some neat tricks here and there in your "tooling" around . This is inspiring , think I am gonna go and try to make a mouse trap now !

"Necessity is the mother of all invention" 

[brewsky]

The mercury sticks showed a difference of just less than 1cm of HG before trying to adjust. I thought that was probably close enough, but tried to adjust them closer anyway. No luck getting them any closer with the mercury sticks. The readings dance around quite a bit (even with the restrictors in place), and any change in one carb also changed the readings on the others.

Hooked up the homemade oil sync outfit, and they showed a much greater difference (as expected). It was slower to react to changes and did not dance at all.

Before adjustment, they showed 9" difference between highest and lowest carb. After much fiddling back and forth, I finally got the max difference down to 6" on the oil tubes. Here also, changing one alters the readings on the others, and you seem to be just chasing your tail in the process.

The oil tubes are definitely more sensitive to adjustments and can be read easier due to the greater travel of the oil levels.

 

[brewsky]

Here's a pic of my DIY sync outfit......

It's 57" tall and about 7" wide, probably doesn't need to be quite that tall. Standard airline tubing from Wally World (2 25' packs) and 2 plastic T's, and a few staples.

[Bailgang]

Here also, changing one alters the readings on the others, and you seem to be just chasing your tail in the process.

+1

[brewsky]

I also have a home made version with oil instead of mercury I haven't had a chance to try yet.

Baby seal or virgin olive? 

nice working coming up with another method....

Thanks!...........10-30 Quaker State

[aperry]

Here also, changing one alters the readings on the others, and you seem to be just chasing your tail in the process.

+1

Yeah, big +1 for me.  I've been running with bench-sync'd carbs for 500 miles for this reason alone.  After a fair degree of frustration trying to sync the carbs the with mercury gauges, I finally gave up and did another bench sync as carefully as possible which resulted in the mercury levels being pretty close. 

Is this inherent to the mercury gauges, where adjusting one carb affects the others?  Would the dial gauges work better in this respect?  I started wondering if the common mercury reservoir shared by the four mercury gauges would somehow allow this to happen.

[phil71]

there's some force against the throttle shaft, and if you adjust too much, it'll definitely affect the position of the others. On the old bikes, I like the needle gauges better than colortune or mercury, but if you turn the adjusters in very small increments, you should see less movement on the others.. and it'll be less frustrating.