Topic: Ball Bearing Carb Bench Sync (PD Carbs)

[Gordon]

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.

Changing the slide height of one carb actually affects the vacuum of all cylinders.  It's a function of the interplay between the cylinders and carbs and not an issue of which type of vacuum gauge you're using.

This is why it's almost impossible to synchronize four carbs with only one gauge, and nearly as difficult to convince someome of this fact who has never synchronized four carbs before. 

[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.

Changing the slide height of one carb actually affects the vacuum of all cylinders.  It's a function of the interplay between the cylinders and carbs and not an issue of which type of vacuum gauge you're using.

This is why it's almost impossible to synchronize four carbs with only one gauge, and nearly as difficult to convince someome of this fact who has never synchronized four carbs before.

Thanks Gordon and Phil.  Great info.  Sounds like I can stop blaming the gauges! 

[Gordon]

Sorry.  After rereading my post it sounds like I was directing that last part toward you, which wasn't my intention.  There have been many questions and suggestions in the past about using a single or double gauge for synching a sohc4, and it's always difficult to explain this concept to someone who's never experienced it hands-on before.

[aperry]

Sorry.  After rereading my post it sounds like I was directing that last part toward you, which wasn't my intention.  There have been many questions and suggestions in the past about using a single or double gauge for synching a sohc4, and it's always difficult to explain this concept to someone who's never experienced it hands-on before.

No worries, I completely understood what you meant.  And thanks again. 

Brewsky, sorry for hijacking the thread. 

Aaron

[750resurrection]

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.

 I'm on this side of it all. I think they freaked because ball bearings is a superior, faster, more accurate method.

 Good job to the OP ( original poster ).

 

[TwoTired]

Cylinders suck.
They suck harder when a slide is near closed and when the cylinder sucks more often (higher idle speed).

When you change the contribution to idle speed on one cylinder, it changes the vacuum reading on all others BECAUSE of the speed/pulse frequency change.  That's why you designate a master carb and adjust all others to its current reading regardless of what it is at the time of adjustment.


edit: Ok, I'm late to the party and could have just said "me too".  But I had this typed up while others posted, and it just looks too good to throw away. 

Cheers,

[750resurrection]

 Good to know TT - repetition is helpful to me because it verifies info. I made a carb sync so hopefully I'll be doing that soon.
Only had two handy vacuum gauges so glad I didn't go that route now.

 I'm also the type that has to know the how and the why of it. Must know exactly why.

[Inkscars]

I tried to bench sync my pd carbs 3 or 4 times. I rode it. For 4 seasons...... I bought a set of vacuum gauges and wonder why I even wasted my time with that crap. After riding it and saying, yea it's fast, for years I discovered it was just dumb luck. I think I am going to actually record a vacuum sync tutorial just to show how naive I was.
After 3 or so years on the forum telling people it was good enough, I want to now go back in time and slap my 26-27 year old self and tell her to do it right. Nothing like a fresh vacuum sync and a snap to WOT and it actually tears your hands off the bars.

[750resurrection]

 That's a motivator for me Inkscars.

 I just got in from doing the cam chain tensioner - static TDCC +15deg method and when I loosened the lock bolt the tensioner snapped in quite audibly. 

 So I guess next is a valve/rocker clearance check then I'll do carb sync. (after I'm sure #2 carb has a working needle and good enough accel diaphragm. ( I knew both were skiddish but the needle worked fine before I pulled em again).

 Anyway, I can hardly wait till my heap really zips.

[78whiteorbs]

nice manometer- I used two stroke oil in my so I could see it better- plus just look at how pretty it is   

manometer

[750resurrection]

 Hey wait it says Yamaha on top...

 ( you did that too ) tsk tsk ! OO lol ( it looks good kinda jelly I just did sharpie marks)

 Ok, I'll go take a quick pic. BRB

[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.

As a follow up to this theory, I closed all 4 slides by completely backing off the idle adjuster and trying to ensure each slide was individually bottomed out with the individual adjusters (carbs 1,3, &4).

It is difficult to tell exactly where each reaches the bottom without turning too far since they are spring loaded and there is no abrupt end to feel. If you turn too far, the linkage arm simply begins to turn the wrong way instead of remaining at a stop.

After adjusting them equally closed as best I could, they still dropped the bearings at different times when checked.

[brewsky]

nice manometer- I used two stroke oil in my so I could see it better- plus just look at how pretty it is   

manometer

78,
Do you have a vid of them balanced?

Would by good to see just how close they can be adjusted with the DIY oil tubes?

Or anyone else on how close you can get with any method?

[andrewk]

I can get them damn close with my needle gauge set- maybe 1/2-3/4" Hg between highest and lowest.  Make sure you go in order, number 2 is the master carb. Set 1 to be the same as 2, then 3 to be the same as 1&2, then adjust 4.  It usually takes me a couple of passes around to get them dialed in perfect- keeping the locknut partially torqued helps the reading stay steady when you tighten down the locknut fully.

The closer you get them adjusted, the better it's going to run.

[750resurrection]

nice manometer- I used two stroke oil in my so I could see it better- plus just look at how pretty it is   

manometer

78,
Do you have a vid of them balanced?

Would by good to see just how close they can be adjusted with the DIY oil tubes?

Or anyone else on how close you can get with any method?

My Throttle Sync


Ehh crap nevermind that's actually a saber cycle one.

[phil71]

Brewsky , your method is going to yield one out of whack rack

[brewsky]

Brewsky , your method is going to yield one out of whack rack

How do you figure that?

The max difference was about 1 cm (less than 1/2") of HG after the bench sync., and that was before I tried to get them closer. That was with a Motion Pro mercury stick set.

I don't have the specs for a 550, but the 750 service manual says 1.6" HG is target.

[DustyRags]

What I'd love to see (and notice I'm not the idiot who's going to pull the carbs off his/her bike just to check this!) would be a video that has a) a proper bench sync done with all the marbles dropping at the same time (or a drill bit I guess, but that's much less dramatic on video), then shows the mercury/oil/gauge levels before the vacuum sync, then again after, and then shows the drop sequence on the marbles again. Is the vacuum method more accurate (meaning all the marbles would fall at *exactly* the right moment) or is it more specific (meaning each gauge has the same vacuum pressure, regardless of slide position).

[750resurrection]

Well dusty, say one cylinder has more compression or better valve seating etc. - It moves a bit more air in or less.

 Right there is a reason the slides should NOT all be exactly equal - and very slight differences would change the "vacuum" to equalize the hard suckers or weak ones...

 "The Pile" is going to appreciate me changing the perfectamundo bench sync.

 

 

[aperry]

I was about to ask what people would consider a "very good" pressure range resulting from a vacuum sync, and then whether people should really expect to get them any better that Brewsky's sub-1cm bench sync.  Then I watched the video posted by 750r.  From what I can tell it starts with a range above 1cm, but then the video skips to the final result of the tuning which seems to be very close, well under .5cm. 

I'll take another stab at this in the spring.  Removing the tank and installing longer fuel lines (or alternate tank) is such a PITA. 

Aaron

[DustyRags]

Sure, it's gonna be different, but how different?

Curiosity hasn't killed this cat yet, but it's strictly a matter of laziness that keeps it that way.

[brewsky]

nice manometer- I used two stroke oil in my so I could see it better- plus just look at how pretty it is   

manometer

78,
Do you have a vid of them balanced?

Would by good to see just how close they can be adjusted with the DIY oil tubes?

Or anyone else on how close you can get with any method?

My Throttle Sync


Ehh crap nevermind that's actually a saber cycle one.

That's pretty close for a mercury outfit.

That manometer is the same as the Motion Pro I used.

Note that the lines are 2cm apart (about 0.8"), so you can easily see differences smaller than 1/2" HG.

On most dial guages, you are hard pressed to read TO 1/2" HG
.......but that is plenty "good enough" to meet the tolerance of 1.6" HG stated in the Honda manual.

The DIY oil manometers magnify the readings even further than the dial gauge or mercury versions, and therefore could allow much closer matching of the carbs.

The value of that is debateable, however, since the spec doesn't call for any closer tolerance than the dial guages read anyway.

The main problem with the most DIY oil versions, is that you need to have the carbs fairly close to begin with, or the oil will be sucked out of the tube before you can make any adjustments. AND, any slight adjustment of the screw makes a mugh larger movement on the tubes.

If you do a precise bench sync by any method, and then make ANY adjustments during a vac sync, the balls wil not drop simultaneously, but that's ok, since there, you are syncing air flow rather than mechanical throttle position as previously stated.

It just so happened that my bench sync ended up being within the tolerance, so any further adjustment wasn't necessary, but I tried to go a step further anyway, with limited success. The closer you get to "perfect balance", the harder it is to adjust one without screwing up another.

I would still like to see a vid of perfectly balanced oil tubes if there is one out there!

[750resurrection]

Yes, supersensitive on my home made. Very good explanation, and no I did not get even tubes of oil - when I finally got #1 to behave and not drop ( the effective region of turn on the slide screws was about 1/4 to less than 1/2 a turn, or that particular oil tube would sky up, or drop and bubble it all).

 So yeah, with home made it was a hassle in the sense I hard to start and kill it 100 times till I got them dialed in close enough.

 I only had it running for maybe 60 seconds once while I took a pic - the oil tubes were 1" to 2" apart I'd say and not even.
 My 750 is not rebuilt nor are new parts in use ( plugs, caps, wires, dyno ign - yes) that would affect this system other than those.
 I hacked the carb together even made some o rings with some spin sanding.... so I definitely think someone could do better - slide #4 screw and tab part are twisted on top...
 

 Let me just say though I took a run late last night when I was finally done and it is a huge world of difference - my handlebars do not buzz, the mirrors are not shaking unbelievably - and I could chug it in 2nd gear coming in not touching the throttle and she just tugged and tugged and kept going - no stalling, no couching and crappy jerky throttle... it was smooth and very enjoyable...

 Here's another twist I cannot explain - I synced it once yesterday after valve lash check, then came back after car errands - when starting I heard a tick in head - thought maybe I didn't tighten down a rocker set net... so with the carb tuning on it, I redid the valve lash check... then back to a few HOURS of screwing with the carbometer...

 Finally finished up late after 10pm, and get stuff put away a bit and I see #1 spark plug wire resting on the coils where I put it when redoing the valve re-check.   

 Well, I had it stable a few different times, not sure how with a gas washed non firing cylinder - not sure how I didn't notice other than runs were only a few seconds at 1500 or below... LOL
 
 Guess I had better take another stab at it with all plug wires on...  - in any case it ran fuhhhreaking great ! I mean night and day difference.

 Okay shaggy dog spew over.

[DustyRags]

That's actually very encouraging. Mine started arcing out of a cap, which of course I noticed right after I got it all dialed in as well. So now I have new caps in hand and need to go put them on and do it all again.

[750resurrection]

 Hmm... I'm waiting a bit and opted for 4Q Rotella T 15w40 - saw the Jaso MA on the back as this site tutored.
 So I go to the local non big box shop guy I've known for years for oil filter and have him take a listen to the ticking I heard that scared me....
 
 He points to the top of the exhaust flange #1 says leak there - "That's the tick?!  "
 " Yep "

 Sure enough there's dark oily carbon on top of the flange vanes. I put a smoker in front of those and had my hand all around there past two days trying to "detect" a leak... 
 I guess we forgot visual inspection...

 On the upside after all the extra work, it's not the top end or a valve or rocker going wacko... 

 HAHA ! FREAK ! So I kinda hammered it a little today - shifting at 6 or 7 k is not my strong point....

 So I'm putting off resync in favor of oil and filter change it's only like 6 years old oil in there, full of gas wash and who knows what else. Authentic 20w50 Honda Spectre though so we know it held up...
( that was a pure noob idiot brag comment I have no freakin idea believe it )

 Ok, so with exhaust leaks at engine exit (large on #1, smaller on #2) I'm off on my "carb tune" and my " sync" I do believe once the leaks are fixed.
 
 Yeah freaking forget it for now seals are on order... I might wrap in there with some hammered copper house wire... LOL