Topic: How important is vacuum sync?

[Kevnz]

Well, Gents. Thank you for your opinions. That really clears things up . Not. By my count back we seem to be pretty much equally divided between imperative, yeah nah, and waste of time and effort. Even between mechanics back in the day there seems no consensus. That's not quite accurate, I think all agree that vac sync can get the carbs perfect, just that whether that last tiny bit is worth the time , effort and expense. I have 2 bikes, but one will (hopefully ) soon be sold and it's running well enough. The other one has not yet been started, so is an unknown quantity. The carbs were mint when I dismantled them, so maybe they haven't been dicked with. This particular bike will be my keeper, so I would like it to be as good as possible; we'll see how it goes and if necessary, invest in a set of guages.
Thanks again.

[ofreen]

Not that it matters much, but I am in the 'syncing is useful' camp.  As others have pointed out, it doesn't make any real  difference at higher throttle openings, but it helps with these rattly old engines at idle.  I still have the  PCCC tool I bought back in the 80's or maybe the 70's.  In spite of the fact that the deadly mercury in it has killed me 5 or 6 times, I am glad I've had it, even though I use it infrequently.

[scottly]

Greg, do you remember the guy that revved the motor and snapped the throttle closed while tuning with mercury sticks? He looked at the gauge to find all the mercury gone, having been sucked into the motor and vaporized out the exhaust. The term "mad as a hatter" came from the use of mercury when making hats...

[Trevor from Warragul]

Speaking of syncing carburetors, this job is an absolute nightmare on a Honda CBX!  The CBX is so sensitive that when the carburetors are out of sync, the primary chain behind the clutch will start to slap, and this will make the clutch basket knock.  The Prolink CBX cured this somewhat with a tensioner on the primary drive and a redesigned clutch basket (my CBX has a Prolink basket).  I ended up buying 2 carburetor adjusting screwdrivers & cutting one right down (actually, I forgot that I have a 3rd one that I've also been meaning to modify).  This way, I can adjust 2 carburetors at the same time.  I also smashed the plastic handles & welded on little metal T-bars.  Why?  Because, after a while, I realized the weight of the plastic handle was enough to throw off the adjustment!  Because of this anal retentive attitude, my CBX is one of the quietest twin shocks at idle I've ever seen...

[dave500]

im with ofreen aswell,proper sync makes the transition off idle smoother,for guys who putter around town bar hopping it makes for a nicer ride all over,ive synced a coupla guys older twins of other makes and they remarked how much better it felt,the guage didnt show much difference at the start but straight away the idle becomes nicer,thats all after the ignition was squared away perfectly,ya cant half do things,a half baked ignition tune and bench sync just aint as good full stop!!once synced they will stay put until someone #$%*s with it.

[Deltarider]

If I have managed to bench sync within 1,5 cm Hg and the choice is between that result and spend I don't know how much time to try to equalise another cm Hg, the choice is easily made. I did all methods, but I choose to save my bike an idling time that can easily extend to over 30 minutes annoying the neighbours no end. That is and has always been my point because idling is the rpm worst as far as engine wear.

[PeWe]

All carbs affect each other too. I adjusted one to see that the carb beside changed. So it can take a while to get all equal. One can be wrong due to the other .......

Important to slowly increase throttle and see all gauges move in parallel up to 3000rpm, not only equal at idle.

[Stev-o]

All this talk about sync has got me to thinking maybe I should break out my Honda factory gauges and check my carbs!   

[maxheadflow]

I thnk you might want to fix the gauges first..

FWIW, Don't dismiss the ability for using vacuum gauges as a diagnostic tool.  One of the reasons why they used to use vacuum gauges on cars.  If the the carb sync it different from idle to say 4000 and won't adjust out, there could be something wrong with motor, pipes, carbs.  I've seen it more than once where it helped to diagnose a weak cylinder.   

If you own the bike and ride it, yeah sure, you can kind of figure out if the carbs need syncing. If the last time you synced the carbs, there weren't any adjustments, next service you can skip it.  Bike comes in for a tuneup / service, you don't know the condition of the bike. 

[ofreen]

The term "mad as a hatter" came from the use of mercury when making hats...

No question mercury is toxic, but people these days act like it is on par with plutonium.  A few years ago, someone dropped a mercury thermometer in one of the grade schools here.  They closed the whole school, something that has been repeated all around the country.  Seems a bit of an over reaction to me considering how we used to play with mercury in chemistry class when I was in school.  All that is needed is some common sense when handling it, just as with acetone, MEK, lead, gasoline, used motor oil, charcoal, beer, the list goes on.  Now they are going after Round-Up, apparently because some people take baths in it. 

[70CB750]

The term "mad as a hatter" came from the use of mercury when making hats...

No question mercury is toxic, but people these days act like it is on par with plutonium.  A few years ago, someone dropped a mercury thermometer in one of the grade schools here.  They closed the whole school, something that has been repeated all around the country.  Seems a bit of an over reaction to me considering how we used to play with mercury in chemistry class when I was in school.  All that is needed is some common sense when handling it, just as with acetone, MEK, lead, gasoline, used motor oil, charcoal, beer, the list goes on.  Now they are going after Round-Up, apparently because some people take baths in it. 

LoL, they think mercury kills on sight or touch - same as asbestos.  I dont care to remember how many mercury termometers I broke as a kid. 

[craz1]

Yes you have to be careful with the mercury. As a commercial HVAC tech we replaced hundreds of old Honeywell stats that had the mercury bulbs. I built a set of mercury gages in the 70's when you could buy mercury easily. I decided to get rid it them due to the safety issue. However after trying all of the other gages out there, Morgan tune, Motion Pro, nothing could compare with the mercury gages. So I had the idea of reusing the mercury from all the stats I removed. Took a while to get enough for a new set of gages.

[PeWe]

Smooth take offs/roll offs from idle to 3000-4000 rpm makes the ride to a joy.
I hunted the correct jetting for my K6 with TMR flatslides. I adjusted  fuel jets up and down to solve the uneven engine between 2000-3000rpm something.

I gave up, synched the carbs and solved it. Last time was with another cam.

[BenelliSEI]

I will bet that everyone who bench syncs and thinks it is good would be very impressed on how much better it is after I spent a half hour with my gauges. Until you use the gauges you have no idea how little of an adjustment can cause changes in the vacuum. Also, changing one can affect the others. Dan

That’s the bottom line. Total agreement..

[Whaleman]

I will bet that everyone who bench syncs and thinks it is good would be very impressed on how much better it is after I spent a half hour with my gauges. Until you use the gauges you have no idea how little of an adjustment can cause changes in the vacuum. Also, changing one can affect the others. Dan


That’s the bottom line. Total agreement..

WOW Thank You, Dan

[dave500]

some guys have toyed with using one guage and swapping as they go to set sync,it aint gonna happen they gotta be visable each in real time as touching one can alter another,its a bit of an art but anyone with mechanical aptitude will do it ok,some guys cant even get the tank of without some bother?

[PeWe]

It is also a good thing to verify the function after engine, ignition job with tank off.

But you need an extra tank with petcock to hang in the ceiling or stand with fuel hose to bike. It was not cheap but well invested money. Used it much more than I thought when ordering it.

I hang the Morgan Carbtune around petcock.

[dave500]

i got an old weed wacker tank on a tripod,guage unit sits on it aswell,too easy.

[Whaleman]

I built a temp tank out of pipe fittings. Dan  EDIT: Does anyone know why my pictures post off 90 degrees but when you click on the they show correct?

[StockRider]

I built a temp tank out of pipe fittings. Dan  EDIT: Does anyone know why my pictures post off 90 degrees but when you click on the they show correct?

Dan, I'll PM you about your picture question. It is outside of the thread topic and may reveal some things that don't need to be seen by all.

[BenelliSEI]

My original remote fuelank was a $0.99 turkey baster. With the bulb removed. It was a bit small, very happy with my remote Motion Pro bottle.

[70CB750]

I usually use tank I take from a tiller, works well

[mrbreeze]

The term "mad as a hatter" came from the use of mercury when making hats...

No question mercury is toxic, but people these days act like it is on par with plutonium.  A few years ago, someone dropped a mercury thermometer in one of the grade schools here.  They closed the whole school, something that has been repeated all around the country.  Seems a bit of an over reaction to me considering how we used to play with mercury in chemistry class when I was in school.  All that is needed is some common sense when handling it, just as with acetone, MEK, lead, gasoline, used motor oil, charcoal, beer, the list goes on.  Now they are going after Round-Up, apparently because some people take baths in it. 

I recall playing with Mercury back in grade school in the 60's. One kid was showing us how shiny it made a dull old nickel. I don't recall breaking open thermometers to get more but I remember it was years after that when I learned it was hazardous. It's a wonder kids from the 60's are alive today. We routinely did all kinds of things that are forbidden today.

[maxheadflow]

Here is pic of my fuel tank for syncing carbs. It was made back when they used to sell fork oil in steel cans.