Topic: Carb sync frequency

[callbr549]

How often will the carbs on my 1972 CB750 need to be synced? I am considering buying the MotionPro Sync Pro gauges, but at close to US$100, I'm not sure I will use the gauge often enough to justify the expense. If its something that only needs to be done once a year or less, I'll probably take it to a mechanic who has a gauge. If its more often I would rather buy the gauge.

[Johnie]

At around $75 an hour you would be much further ahead to buy those gauges and do it yourself.  Plus, nice satisfaction to maintain your own bike.  Unless the sync gauge will be the only tool you own, I would spend that $$$ on the gauges rather than pay the dealer.  I like to check my sync annually.  Not a big deal once you do it. 

[HondaMan]

On a K1-K8 (and 'F'), it only needs to be done when the bike is new or if you do a port job. Disassembling the carbs for cleaning, so long as you don't disturb the nuts on the tops of the shafts, won't disturb the carb sync, either.

Generally, the carb sync thing is overrated and overdone, in my experience. Even back in the day, it was one of those things that customers would request (even demand), and we'd go to all the trouble of hooking up, getting the fan out, annoying the shop with the noise, only to discover that they were still well within specs. The balance doesn't wear that much.

In the days of the CB750K0, yes, it was an issue. The Four came with 4 cable-operated carbs, and the cables stretched forever. The result was uneven pullaway performance at stopsigns and the like, and vibration at highway speeds. When the GT-style linkage came out, we found that Honda's new advice was spot on: adjust when new, check at 1000 miles, then after rebuilds. Those of us who also hotrodded the engines added, "after port jobs" to the list, which Honda never would... 

[Soos]

Those of us who also hotrodded the engines added, "after port jobs" to the list, which Honda never would... 

REALLY?
I hadn't thought of that.
How far off would you see them with a port job?


Personally I probably do it more often than needed, but I really like how my bike idles and rides at low rpm with the carbs synched as close as I can get them.(then I re-check them 300- 1000 miles later, picky.)
But 1 time a year at minimum, depending on how much carb meddling. I have gone through 4 sets of carbs on my cb650. Finally ended up with a nice CV set of carbs.



l8r

[Duke McDukiedook]

I bought the motion pro synch at about $80. The fluid got sucked out the last time I synched my carbs in October when I was having idling problems. I am not very pleased with it at all, I would spend your money on something better like maybe a morgan tuner or one of those fancy $180 gauge sets. When the fluid got sucked out of the motion pro I just used an acctron vacuum gauge (single, about $24 at Sears) on each carb to adjust the readings. It got a little tedious switching between each carb to get it aroound 9psi vacuum, but it runs better now. Synching the carbs is one of the last things you do when giving the bike a tune-up as far as I am concerned. Not one of those things you want to have to do too often, I am sure my neighbors love it when I am running my bike with a fan on it at 10 in the evening 

[Deltarider]

Generally, the carb sync thing is overrated and overdone, in my experience.

+1

[bryanj]

500 handbook originally said every 3,000 mile or 6 months as did later reprint
GL 1,000 said every 7,500 mile.

Havent got a 750 handbook

BUT-----EVERYTHING else must be done first

[Soos]

BUT-----EVERYTHING else must be done first

+1

[Deltarider]

My experience is that I can ride for years and tenthousands of kilometers and still there's no need to synchronise. As a matter of fact all syncs I performed were not needed and were done out of curiosity and a desire to play.
Tip: when you have adjusted put a little Loctite on the adjusters.

[eldar]

Yeah, I hardly ever sync. If I notice some extra clutch noise, I might check it just in case but things are usually ok.

I have argued with people about syncing. Many seem to think the sync should be done before tuning the a/f mix but the manual says it is the last thing and that is how I do it.

[crazypj]

Those of us who also hotrodded the engines added, "after port jobs" to the list, which Honda never would... 

REALLY?
I hadn't thought of that.
How far off would you see them with a port job?


Personally I probably do it more often than needed, but I really like how my bike idles and rides at low rpm with the carbs synched as close as I can get them.(then I re-check them 300- 1000 miles later, picky.)
But 1 time a year at minimum, depending on how much carb meddling. I have gone through 4 sets of carbs on my cb650. Finally ended up with a nice CV set of carbs.



l8r

 The reason for doing it after porting is simple, you'll probably have the slides out to adjust needles plus,  the ports may not flow exactly equal.
I check when I think about it ( maybe once a year or so, sometimes 2~3 yrs if I haven done much mileage)
 Gauges don't wear out so even paying $100.00 or more is just an investment, unless you intend getting rid of bike(s) in a few years ( even then, the prices will have gone up so you can probably recover costs)
PJ
PJ

[markjenn]

I guess I'm somewhere between the "no need to ever do it unless you disassemble the carb banks" and the "do it every tune up" groups.

If you just care whether the engine runs Okay, you generally can do it once and pretty much forget about it in normal maintenance.  But if you really care about a smooth idle and taming the buzziness that often plagues inline-four bikes, doing it now and then (whenever the engine seems to be running a little less smoothly than it did or perhaps every 10K miles or so) is a good idea.  And I think anytime you take the carb bank off, whether you disassemble or not - you probably need to at least check it - we're talking about minute differences in carb mechanics here and most carb banks need to be tugged and pulled quite a bit to get them in/out of the bike.

I gave up on mercury manometers a long time ago - hard to store, really nasty for the environment when you eventually get rid of the things, and many units start to have problems where the mercury tends to get air pockets in the tubes.  I've got a Morgan Carbtune now and that thing is wonderful.  But I'm a tool junkie and believe life is too short to put up with doing maintenance with crappy tools.  I suppose you could do all the other tuneup stuff and just take it into the shop for the carb balance, but what a hassle, and they['ll probably charge you their minimum shop setup time which could be an hour or more.  And my experience is that this is a finicky type of procedure where being careful really pays and most of the monkeys at shops are just going to thrown the thing on the balancer, see that it's not too bad, and call it good to go - $100 wasted for nothing.  That's probably enough to get a Morgan that will last you the rest of your life.  There's being frugal and there's being cheap.

http://www.carbtune.com/

- Mark

[OldSchool_IsCool]

I'm thinking of permanently mounting mine to the handlebars.  Chicks Dig Gauges!

[HondaMan]

I'm thinking of permanently mounting mine to the handlebars.  Chicks Dig Gauges!

+2! 

[Johnie]

I agree with MarkJenn...the Morgan is what I bought in 1999 and they are fantastic.

[ev0lve]

I bought the motion pro synch at about $80. The fluid got sucked out the last time I synched my carbs in October when I was having idling problems. I am not very pleased with it at all, I would spend your money on something better like maybe a morgan tuner or one of those fancy $180 gauge sets. When the fluid got sucked out of the motion pro I just used an acctron vacuum gauge (single, about $24 at Sears) on each carb to adjust the readings. It got a little tedious switching between each carb to get it aroound 9psi vacuum, but it runs better now. Synching the carbs is one of the last things you do when giving the bike a tune-up as far as I am concerned. Not one of those things you want to have to do too often, I am sure my neighbors love it when I am running my bike with a fan on it at 10 in the evening 

Second the overall crappiness of the Motion Pro. Set it up with all the tubes in the collector attached to #1 for adjustment. Start the bike. Goodbye fluid.

Kind of glad I'm not the only one.

http://forums.sohc4.net/index.php?topic=38242.msg419387#msg419387


Very disappointed. They will send a refill kit gratis though. Haven't bothered to try again just yet. Poking around on the board it seems the Morgan is the best of the lot.

[crazypj]

I've never used them or seen them but from the pictures it looks that if the fluid got sucked out you probably had an air leak in the filler plugs.
PJ

[ev0lve]

Filler plugs are the restrictors in the end of the tubes? If we're talking about the adjustment screws pictured then I'd just be perturbed with Motion Pro; the instructions are to turn them all the way out then adjust with all four tubes hooked to the manifold and the manifold hooked to carb 1. Shoulda been easy.

I cut the restrictors out and redid them but talking to the guys at Motion Pro they suggested using a hemostat when hooking them up and starting the bike. I'll try again when I get the front end together but I really wish I'd got the Morgan from reading postings.

Heck, if it fails the second time I try maybe I should just give the set to the OP and let him have a go 

[Soos]

They will send a refill kit gratis though.

thats always good to know!


l8r

[HondanutRider]

I've been thinking about getting a tool for syncing my CB350F, but wonder if it would be worth the effort and cost. 

My 350 bike has low mileage but sat a long time.  I had a lot of carb cleaning to do, but didn't take the rack apart.  It seems to run pretty good now, but there is a low-speed chain rattle from within.  I've checked the cam chain tension but some people claim the noise is common.  I was theorizing that maybe the "rattle" might be caused by chain (cam and primary) slap due to the carbs not being in perfect synchronization.  Any thoughts on this?

The other other thing I've researched is how to build a simple manometer or pressure diff gauge from a long loop of clear hose filled with fluid, such as transmission fluid.  Each end of the loop is connected to a carb vacuum lead and the looped hose with fluid would show the relative vacuum difference between the two systems.  (This arrangement is what airhead beemers apparently homebrewed for their carb syncing.)  As long as the difference in vacuum isn't too great, the fluid would stay in the loop rather than getting sucked into the engine.  Only problem is, we have four, not two carbs to synchronize.  So, I was thinking...why not join two loops of hose together with a manifold arrangement at the bottom of the loop where the fluid would reside, and then all four ends would balance their vacuum difference with fluid heights.  Any thoughts...or shall I be the guinea pig.

[WHALEMAN]

I look forward to my springtime sync. Dan

[billybobobrain]

Generally, the carb sync thing is overrated and overdone, in my experience.

+1

If you think the carbs need to be adjusted, adjust the valves. They tend to go out of adjustment on a regular bases like every 20k 30k miles. same effect on idle as carbs which should never go out of sync unless you mess with them.

[Duke McDukiedook]

Yeah Iggy, the motion pro sucked all right... sucked mah fluid right out the manometers! 

[ev0lve]

Hrrrrm,

Let's see. 2 reports of Motion Pro suckage. Everyone loves the Morgan. They're the same price just about (after shipping). Morgan wins

55.00 GBP                      =   83.2258 USD
United Kingdom Pounds       United States Dollars
1 GBP = 1.51320 USD       1 USD = 0.660853 GBP

http://www.ekmpowershop1.com/ekmps/shops/carbtune/carbtune-pro-4-column-22-p.asp

[Duke McDukiedook]

Anyone want to trade a motion pro sans fluid for a morgan tune?

[MJL]

The other other thing I've researched is how to build a simple manometer or pressure diff gauge from a long loop of clear hose filled with fluid, such as transmission fluid.  Each end of the loop is connected to a carb vacuum lead and the looped hose with fluid would show the relative vacuum difference between the two systems.  (This arrangement is what airhead beemers apparently homebrewed for their carb syncing.)  As long as the difference in vacuum isn't too great, the fluid would stay in the loop rather than getting sucked into the engine.  Only problem is, we have four, not two carbs to synchronize.  So, I was thinking...why not join two loops of hose together with a manifold arrangement at the bottom of the loop where the fluid would reside, and then all four ends would balance their vacuum difference with fluid heights.  Any thoughts...or shall I be the guinea pig.

There was a 5 or 6 page thread on this a while back, well worth the read.

[eldar]

My mercury tool sorta did that but nothing got sucked out. I have been thinking about getting vacuum gauges and using those. Probably no cheaper but should work just as good.

[ev0lve]

I was reading that vacuum gauges (especially the cheapo ebay types) were pretty tweaky/bounce. Not having used any is that true generally?

[eldar]

Hard to say. I suppose some are but after dealing with a mercury gauge, I doubt they are any worse.

[markjenn]

The other other thing I've researched is how to build a simple manometer or pressure diff gauge from a long loop of clear hose filled with fluid, such as transmission fluid.  Each end of the loop is connected to a carb vacuum lead and the looped hose with fluid would show the relative vacuum difference between the two systems.

The loop may provide some damping, but ultimately it's the height of the fluid column over the reservoir of fluid that you need to measure and the reason mercury is used is because it is a heavy liquid resulting in shorter heights.  Build a manometer with transmission fluid and the height of the tubes has to be much longer, typically 6' or so. It will certainly work fine and if you have a cheap source of tubing and lumber and don't mind a bulky Rube Goldberg contraption in your shop, go for it.  For me, it's just not worth the hassle when there is a relatively inexpensive and welll-made solution available.

- Mark

[feliz]

I made one of the home made manometers, it cost less than $5.00 and workslike a charm. I actually prefer it over my Morgantune for my twin cylinder bikes, I find the fluid doesn't jump around and I hang it off the ceiling of my garage making it real easy to see. Storage is easy I just coil up the empty tubing.

[HondanutRider]

The other other thing I've researched is how to build a simple manometer or pressure diff gauge from a long loop of clear hose filled with fluid, such as transmission fluid.  Each end of the loop is connected to a carb vacuum lead and the looped hose with fluid would show the relative vacuum difference between the two systems.

The loop may provide some damping, but ultimately it's the height of the fluid column over the reservoir of fluid that you need to measure and the reason mercury is used is because it is a heavy liquid resulting in shorter heights.  Build a manometer with transmission fluid and the height of the tubes has to be much longer, typically 6' or so. It will certainly work fine and if you have a cheap source of tubing and lumber and don't mind a bulky Rube Goldberg contraption in your shop, go for it.  For me, it's just not worth the hassle when there is a relatively inexpensive and welll-made solution available.

- Mark

I don't believe the column(s) of fluid would be that high.  What I'm thinking is a column height that would be based on the relative difference in pressure between carburetor vacuums.  That difference of vacuum shouldn't be very significant, and in fact is being tuned/synced to zero.  If, as in a regular manometer, the pressure was relative to atmosphere (open end for positive) or pure vacuum of liquid (closed end for negative), then yes, the column heights would be very unwieldy, especially with a fluid much lighter than mercury.

BTW the spec for carburetor vacuum on the CB350F is listed by Honda to be 16-24 cm of mercury which would work out to be about 7-11 feet of water.  Having never seen carburetor syncing, I would have to theorize that the difference in pressure between two running carbs should be no more than 4-6 cm of mercury, which in a loop of water column should be 2-3 feet. Transmission fluid is a little lighter than water, but not much, so these dimensions for water would still be close for that fluid.  That's still pretty long column (3 feet) that would have to be accommodated, and then even more to allow for bounce or the pulse fluctuations of a breathing engine - however, not entirely unreasonable for a home-brew.  Can someone comment on how much pressure differences they have seen in actual syncing?

[crazypj]

If you blip on the throttle it will easily go to 40~50 cm/Hg when its closed suddenly.
Possible to suck all the mercury out of  gauges (very bad idea , not nice stuff to be breathing after it gets through engine)
Its why I prefer my Honda dial type gauges, you can also do a few test that are not really possible with 'wet' gauges
 I was pretty sure there shouldn't be bleed holes/adjuster screws on the Motion-Pro set up, your supposed to be drawing against a closed container. (but I've never seen/used them except in pictures)
 Morgan works well although I've only ever used them once so can't comment on longevity
Cheap dial gauges work OK but wear out real quick in a shop environment, we averaged about 4~6 months per set. (your mileage may vary  )
 You fit a pilot jet into the tubes to restrict 'bounce' on needles or use thin wall rubber tube as it flexes with vacuum pulses, or, you can ge aquarium clamps to restrict tubes (the clamps that go onto aerators)
Friend in work was in navy, working on carriers when they still used some piston engined planes, he said they dropped 3"~4" pipe into the ocean and would draw 28 ft of water, blew a few engines if pilot/mechanic  'blipped' throttles too quick
PJ

[OldSchool_IsCool]

The trouble with vacuum differential is that the carbs are not under vacuum at the same time.  Vacuum only occurs when the intake valve opens.  That's why the liquid within the tube needs to be tall and/or highly viscus and/or damped pretty heavily.  That's also why the needles of a vacuum gauge like to jump around so much when not dampened.

[markjenn]

All I can say is that I've tried three methods - water manometer, mercury manometer, and morgan - and while all three will work fine, the morgan is just so much easier.  And when the job is done, it slips into its 3"x5"x12" case and gets tucked neatly into my toolbox.

- Mark

[ev0lve]

If you blip on the throttle it will easily go to 40~50 cm/Hg when its closed suddenly.
Possible to suck all the mercury out of  gauges (very bad idea , not nice stuff to be breathing after it gets through engine)
Its why I prefer my Honda dial type gauges, you can also do a few test that are not really possible with 'wet' gauges
 I was pretty sure there shouldn't be bleed holes/adjuster screws on the Motion-Pro set up, your supposed to be drawing against a closed container. (but I've never seen/used them except in pictures)
 Morgan works well although I've only ever used them once so can't comment on longevity
Cheap dial gauges work OK but wear out real quick in a shop environment, we averaged about 4~6 months per set. (your mileage may vary  )
 You fit a pilot jet into the tubes to restrict 'bounce' on needles or use thin wall rubber tube as it flexes with vacuum pulses, or, you can ge aquarium clamps to restrict tubes (the clamps that go onto aerators)
Friend in work was in navy, working on carriers when they still used some piston engined planes, he said they dropped 3"~4" pipe into the ocean and would draw 28 ft of water, blew a few engines if pilot/mechanic  'blipped' throttles too quick
PJ

Hmmm, that's probably why the Sync Pro doesn't work so well. Mine sucked out the fluid on start but I was in the gas a bit while turning it over. Learning is expensive.

Ordered up the Morgan yesterday. $14 cheaper than the Sync Pro (even shipped from UK) and no fluid.