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VM carb set up

Wallowgreen

Wallowgreen

Forum Mentor
Past Site Supporter
I've just ordered o-rings from our friend at cycleorings, gaskets, boots and the rest of the stuff to do a complete tear down and rebuild of the VM carbs on my '79 GS850GN. The only part that concerns me a little about doing all this is the set up afterward. I've read all the resources I can find both here and other places and have a question about how difficult / tedious it is to sync the carbs.

Do you experienced people here think it necessary / really advisable to use a manometer or have you been able to set up rebuilt carbs without? Adding another $80 ish to the cost of the parts almost doubles the price of the rebuild. Can a manometer be found at a tool rental place?

Thanks in advance again.
 
Carb synching is easy once you've done it the first time. It's a must if you want to get these bikes to run spot on plus it's a regular service check (3000 miles / 6-monthly in my book).

The gauges are well worth the investment and once you know how to use them you can charge your mates a few $ / ? and soon get your money back.
 
I've never seen anywhere that you can rent a manometer.

You can get the synch close (sometimes) with the bench synch, but you really need to synch them with a manometer. I think there are other members in your area? Maybe you could borrow one or pay them to do it.
 
Alright, so assuming no one comes forward locally to either let me borrow a manometer or help me do the job, any recommendations on what type to get and where from?
 
Wallowgreen said:
Alright, so assuming no one comes forward locally to either let me borrow a manometer or help me do the job, any recommendations on what type to get and where from?
Click to expand...

Get a Morgan Carbtune. Period. Worth every penny spent.
 
Wallowgreen said:
I've read all the resources I can find both here and other places and have a question about how difficult / tedious it is to sync the carbs.
Click to expand...

I think most people would agree that actually synchronizing the carbs is a heck of a lot easier than trying to explain the process. Reading up on the procedure will be more tedious than actually doing it.

Do you experienced people here think it necessary / really advisable to use a manometer or have you been able to set up rebuilt carbs without?
Thanks in advance again.
Click to expand...

There's really no way to avoid it. The sync will have a huge impact on how the bike runs.
 
Thanks renobruce.

Been looking on their web site to order one and read about their other product called colortune. Anyone got any experience using that? Is it worth having to help with better/easier mixture set up?

If so I'll get the two as a package deal they offer.
 
Carbtune has received mixed reviews, I'd pass.
Regarding sync'ing, if you are industrious there are tutorials on how to make a sync tool using water or oil - info available on the web if you search. Personally, I'd just spend the money and get the proper tool but wanted to let you know that there are other ways.:)

EDIT, Carbtune has received excellent feedback, it's been Colortune that had been mixed. Sorry for the confusion.
 
Last edited:
I swear by a Colourtune - others won't. I've had mine nearly 30 years and again, once you've used it and made it work you'll wonder what you did without it and how easy it is to use.
 
BassCliff, I've already read those reports as part of my wising up on the process. Actually I use the information available from your website quite a lot so thanks for taking the trouble.

Nessism did you mean carbtune or colortune?
 
Nessism said:
Carbtune has received mixed reviews, I'd pass.
Click to expand...

Really? I've never seen anything but good said about the Carbtune. I swear by it. I always had a slight vibration from my 1150 that I couldn't get rid of....until I bought the Carbtune. The 1150's carbs are super-sensitive, and my old mercury sticks would not dial them in well enough. I don't see how any other synch tool could be more accurate or user friendly.

As far as the Colortune, I have one of those, too, with plugs for both my bikes. For me it seems to work well on the CV type carbs, but not as well on the VM's. They are good for getting your pilot settings close, but I think reading the plugs is still the only way to get everything spot on.
 
This is most probably a stupid question but aren't VM carbs mechanical? If they are, how is it that if they're bench sync'd correctly, would they need to be vacuum sync'd with a manometer since all the slides would be moving at the same rate?

Thanks for your indulgence.

Don
 
don_gibb6512 said:
This is most probably a stupid question but aren't VM carbs mechanical? If they are, how is it that if they're bench sync'd correctly, would they need to be vacuum sync'd with a manometer since all the slides would be moving at the same rate?

Thanks for your indulgence.

Don
Click to expand...

Bench synchs are never spot on. Plus any variation from cylinder to cylinder (valve clearances, compression, etc.) will change the demand of each carb.
 
Thanks for all the help and suggestions chaps. Ordered a Morgan carbtune and colortune as a package today. Plan to do the tear down and rebuild over the Christmas break so I'll let you know how it goes with the new gear.
 
renobruce said:
Really? I've never seen anything but good said about the Carbtune. I swear by it. I always had a slight vibration from my 1150 that I couldn't get rid of....until I bought the Carbtune. The 1150's carbs are super-sensitive, and my old mercury sticks would not dial them in well enough. I don't see how any other synch tool could be more accurate or user friendly.

As far as the Colortune, I have one of those, too, with plugs for both my bikes. For me it seems to work well on the CV type carbs, but not as well on the VM's. They are good for getting your pilot settings close, but I think reading the plugs is still the only way to get everything spot on.
Click to expand...

Oops, ment to say Colortune has received mixed results.:oops: Carbtune feedback has been steller.:D
 
don_gibb6512 said:
This is most probably a stupid question but aren't VM carbs mechanical? If they are, how is it that if they're bench sync'd correctly, would they need to be vacuum sync'd with a manometer since all the slides would be moving at the same rate?
Click to expand...
Actually, if you look at the CV carbs, the part that actually causes the vacuum is mechanical, too. :-k

The vacuum-operated slides do nothing to cause any restriction (therefore, vacuum) at idle and low throttle openings. It is the mechanical butterfly-type throttle blades that are adjusted during a sync, whether it's a bench sync or a vacuum sync.

With either set of carbs, the bench sync only gets the throttles rather close, the vacuum sync is what really sets them correctly. :D

By the way, congrats on your new toys. Feel free to ask for help on how to use them when you get them.

.
 
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