Author Topic: Carb sync (Read 51116 times)

Pinhead · « **Reply #150 on:** June 12, 2006, 10:16:03 PM »

I'd say if they're not equal after setting the throttle slides, it'd be an air bleed screw somewhere, not exactly sure of what type of carbs those are. On my 650, the idle adjustment is just a throttle stop. On some others, you actually adjust each carb's idle with an idle mixture screw. If those are different, the carbs will need to be synched. (That word does look kind of weird now that I look at it).

TwoTired · « **Reply #151 on:** June 12, 2006, 10:46:31 PM »

In a perfect engine, each of the pistons will displace EXACTLY the same amount of air.
In a perfect engine, each and every piston ring leaks EXACTLY the same all the others. (zero)
In a perfect engine, each of the head chambers have EXACTLY the same amount of volume.
In a perfect engine, each of the valves open EXACTLY the same height.
In a perfect engine, each of the valves leaks EXACTLY the same amount as all the others. (zero)
In a perfect engine, each of the cam lobes have EXACTLY the same profile.

In a perfect engine, each of the cylinders draw EXACTLY the same amount of air. (See above)
In a perfect engine, each of the carb slides will be open EXACTLY the same amount for all cylinders to fire with the same strength.

A perfect engine is practically impossible. But, even firing pulses from each cylinder can be approximated by feeding each cylinder with a similar charge of fuel/air mix. And, this is acheived when the vacuum present on each intake runner presents the same conditions to identical carburetors.

It's called synching the carburetors. However, the goal is to get all the cylinders to fire evenly.
Now you know why a compression check is good to have done. (cylinder volumetric efficiency check)
Now you know why tappet adjustment and all the tuneup items need be addressed before synching carbs.

Now I'll stop typing,

Cheers,

Bob Wessner · « **Reply #152 on:** June 13, 2006, 02:21:47 AM »

Quote

I checked all mine visually everywhere from closed to WOT and they all seem to be in the exact same position.

Dave,

They may "appear" to you as being equal or even, visually, but believe me, it takes v-e-r-y little difference to make them out of sync. I doubt that most people could visually detect it unless they were way out. Next time you have the bike warmed up and running, see just how little throttle movement will affect the engine sound. On mine it almost seems like all I have to do is think about it.

I have the 4 into 1 set-up also. They are prone to changing, so it is wise to check them periodically. Which is also why Honda ditched this arrangement on subsequent models.

eurban · « **Reply #153 on:** June 13, 2006, 04:16:49 AM »

Continuing on the path that TT started . . . .If you bench synch your carbs very carefully so that the slides are open the exact same amount at a given throttle setting and then you find (using guages) that the actual vacuum being pulled by each cylinder is the same, does this indicate good things about your engine? If the vacuum is a good bit off, does this indicate bad things?

jdpas29 · « **Reply #154 on:** June 13, 2006, 05:47:09 AM »

synching the carbs on my 78 750K made a load of difference in power/response and the way the throttle would come down after goosing it instead of hanging up and being slow to return to idle.

i bench synched them first leaving them on the bike and then set them using a set of 4 vacuum gauges. the whole procedure took about 4 or 5 hours. not bad for 6 beers and 2 cigarettes...

DaveInTexas · « **Reply #155 on:** June 13, 2006, 07:06:53 AM »

Is everyone using the vac gauge method?

Is the homemade method a waste of time? (mason jars, tubing and such)

TwoTired · « **Reply #156 on:** June 13, 2006, 12:01:32 PM »

Quote from: eurban on June 13, 2006, 04:16:49 AM

Continuing on the path that TT started . . . .If you bench synch your carbs very carefully so that the slides are open the exact same amount at a given throttle setting and then you find (using guages) that the actual vacuum being pulled by each cylinder is the same, does this indicate good things about your engine?

I would think so. Or, you were clairvoyantly lucky to err with unequal bench synch on the carbs to exactly match the inequality of the cylinders.

(It could happen

)

Quote from: eurban on June 13, 2006, 04:16:49 AM

If the vacuum is a good bit off, does this indicate bad things?

It can... Think about what happens in the intake runner with a leaky intake valve during compression or firing stroke, or one of the cam lobes rounding off, or a holed piston. These are considered bad things, unless you're the mechanic being paid for repair work.

I didn't mention it before. But, the carb slides wear as they move in the carb channel. This eventually wears out and allows leakage. A whole carb bank would likely wear evenly. A carb bank assembled from different service length sources could have different leakage characteristic across the bank. This would be less than ideal on the perfect engine.

Cheers,

Heirborn · « **Reply #157 on:** June 13, 2006, 04:49:29 PM »

Another vote for carb sync. Makes a huge differnece. Pro Motion sells a basic meter for around $65. Money well spent.

DaveInTexas · « **Reply #158 on:** June 18, 2006, 09:08:12 PM »

Various methods available, wondering what the majority of the crowd does.

TwoTired · « **Reply #159 on:** June 18, 2006, 09:11:27 PM »

I've used a 4 vacuum guage dial set since 1975.

Bodi · « **Reply #160 on:** June 18, 2006, 09:21:54 PM »

Personal opinion follows...
If you have nothing and want to do a carb balance but don't want to blow a fortune, the mercury sticks work great. I would want to be really cautious with them if there are kids around; mercury is an unpleasant nerve poison and liquid metal is irresistable to younguns.
Water methods work, barely, and the equipment gets huge.
Anything that compares only 2 carbs is a waste of effort. Do it once with a set of 4 indicators and you'll notice that any adjustment will affect the other 3 readings. How do you manage that with something that only shows 2 cylinders???
The gauges are ideal if you do a lot of bikes, i would have them if I was a shop mechanic. You can see them from way far away and a real vacuum gauge can be useful for other things too.
For a well equipped home shop looking at working on a few bikes, the Morgan is best. It's durable, accurate, and takes up very little toolbox space.

dafrpa · « **Reply #161 on:** June 19, 2006, 12:13:07 AM »

Got the Morgan based on the reviews here, otherwise I wouldn't have believed the hype. I was not disappointed. It's not huge money for a quality tool that works great!! I was astounded at how fast it arrived, around 4-5 business days from Belfast, Ireland to Ottawa, Canada?! Insane!! No worries about mercury, no bulky water guages...did I mention it works?

Bob Wessner · « **Reply #162 on:** June 19, 2006, 02:01:56 AM »

Not much more to add other than ditto when it comes to the Morgan Carbtune. Everything packs into a neat little pouch for storage as well.

Terry in Australia · « **Reply #163 on:** June 19, 2006, 03:31:13 AM »

Well of course having owned several "classic" Euro-trash bikes (BMW R69S, R100RS cables are magnificent stainless steel items, but my Ducati 900 SS had cables probably made from a fat Sicilian chicks pubic hairs) I always carried a piece of wire for roadside carb synching, and it's still doing duty for "bench synching" my CB750 carbs, (can be done on the bike, but easier on the bench)

My Morgan Carb-Tune that I bought back in 1999 is a wonderful tool, it's much easier to use than individual gauges, and beautifully made. I used to have to run fans to cool the engine when synching my carbs with my old 4 gauge set, but the morgans are so good it takes very little time to get them spot on. Cheers, Terry.

puppytrax · « **Reply #164 on:** June 19, 2006, 03:47:02 AM »

wow...$96USD + S&H...for the Morgan...

Is there a US distributor???

Jonesy · « **Reply #165 on:** June 19, 2006, 05:05:14 AM »

I already did a poll on this once...

http://www.sohc4.us/forums/index.php?topic=959.0

But, it might be good to do again, now that we have more "new faces" on the board.

Terry in Australia · « **Reply #166 on:** June 19, 2006, 05:18:35 AM »

Quote from: puppytrax on June 19, 2006, 03:47:02 AM

wow...$96USD + S&H...for the Morgan...

Is there a US distributor???

Here you go mate, bid on this:

http://cgi.ebay.com/ebaymotors/Morgan-Carbtune-II-Carburettor-Synchronizer-Never-Used_W0QQitemZ4652789618QQihZ002QQcategoryZ43989QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Cheers, Terry.

ken74-550K0 · « **Reply #167 on:** June 19, 2006, 11:06:05 AM »

I use a 4 gauge set purchased from JC Whitney for about $35 (on sale).

http://www.jcwhitney.com/autoparts/Product/tf-Browse/s-10101/Pr-p_Product.CATENTRY_ID:2004169/showCustom-0/p-2004169/N-111+10211+600014252/c-10111

If I were a professional shop mechanic this tool would not cut it, for for home use it's pretty good.

The initial gauge needle calibration is a little touchy (at least that's the way it was on my set) however, after adjusting the dampers it worked pretty good.

tazzmann · « **Reply #168 on:** June 19, 2006, 02:15:35 PM »

I use this one. Awesome set and very accurate...

http://z1enterprises.com/detail.aspx?ID=1695

Tim2005 · « **Reply #169 on:** June 19, 2006, 03:15:06 PM »

Quote from: dafrpa on June 19, 2006, 12:13:07 AM

Got the Morgan based on the reviews here, otherwise I wouldn't have believed the hype. I was not disappointed. It's not huge money for a quality tool that works great!! I was astounded at how fast it arrived, around 4-5 business days from Belfast, Ireland to Ottawa, Canada?! Insane!! No worries about mercury, no bulky water guages...did I mention it works?

This had me baffled for a minute, my Morgan Carbtune is mercury based. Looks like they've changed the design at some point - I've had mine for 15-20 years and it still works great: highly recommended.

heffay · « **Reply #170 on:** June 19, 2006, 03:33:39 PM »

almost 6 days left on that ebay carbtuneII and already at 70 bucks including shipping... i'm guessing it goes for more than you could order one from morgan $:-\$

Ibsen · « **Reply #171 on:** June 19, 2006, 03:37:37 PM »

Morgan Carbtuner

puppytrax · « **Reply #172 on:** June 19, 2006, 04:00:15 PM »

Quote from: heffay on June 19, 2006, 03:33:39 PM

almost 6 days left on that ebay carbtuneII and already at 70 bucks including shipping... i'm guessing it goes for more than you could order one from morgan $:-\$

My thought as well...and while that JC Whitney set is tempting, it's still only 4 cheap gauges...not even a rack to mount them on...

I'm a long way from synching yet...but the Morgan looks like the best bet... $:-\$

DaveInTexas · « **Reply #173 on:** June 19, 2006, 06:28:17 PM »

Anyone have an old Morgan they want to selll?
PM me.

heffay · « **Reply #174 on:** June 19, 2006, 06:55:11 PM »

Anyone have an old Morgan they want to selll?
PM...ME

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What is the best method you have found to synch carbs on a 750?

Author Topic: Carb sync (Read 51116 times)

dafrpa

tazzmann

Ibsen