I was wondering if there is a different way of doing a Carb Synch without using a Vacuum Guage.

A old experienced rider told me that what he does to synch the carbies is when he takes the carbies off for a clean he uses feeler guage to accuratly measure the gap between the butterfly's and the bottom of the carb intake. He justs adjust eash carbie so that they are all the same gap.

Is he on drugs or does this sound like a sound theory?

 

He may be on drugs and it does sound like a theory
But I've never heard of it before. It's dosen't really matter what each carb is set too initially. It's the amount of vacuum each port pulls. The factors for that go beyond just the linkage setting. Tthe only way to equalize them is to have the bike running and hook up gauges.
The gauges aren't that expensive, (Less then $100) and it only takes an hour or so to do on these bikes. I could do it on my last two bikes in less then 15 minutes including warm up time!
For gauges I bought the Morgan Carb Tune II set and this is the third bike I've used them on. No mercury to worry about, and they work great! Google Morgan Carb Tune for a dealer near you. I bought them from www.casporttouring.com in California.

 

Why is mercury free better?

 

There is a certain amount of flutter in mercury guages. Especially the cheap ones. Also some guages are poorly designed and if you give them a big enough rev while connected it is possible to suck mercury into the engine. The Carbtune is an excellent setup. The only reason I am considering this option is that I have to pull the carbies off to get rid of some crap that is in there anyway.

Actually something I remembered back to a Car I had with a twin throat carby. It said to tune the carby you put a screwdriver underneth the butterfly and then put a screwdriver with the same diameter down the other and adjust like that.

 

My ex-SC21 had so worn butterflies that gauges did not show any sensible value.
So there was no other possibility than tune those by hand.
Mechanic did an excellent job --> idling + performance got much better.

 

We set the eight individual butterflies on Hilborn injections like that. All done on the bench. A .002" feeler gauge.

I've driven bikes to well over 100,000 miles without ever doing a carb sync. The theory being, if they've never been messed with, the linkage doesn't move, therefore no change. At least not enough to care about. A complete carb dis-assembly is the only time I've done it.

Many things that are performance issues will effect the vaccuum reading and that's what you're matching with a set of gauges, not the butterfly's position nor that carburetor's flow capacity.

I've seen attempts to sync carbs to solve a performance issue that was actually a plugged idle jet. The vaccuum was different because the hole for that carb wasn't firing, effecting the vaccuum reading on the next intake stroke because nothing had been burned in that hole, which has an effect on the vaccuum. After moving that butterfly to try to match the air flow and the performance was still bad, although the vaccuum was matched, the carbs were dismantled, the jets cleaned out, and then the sync needed to be redone to put the carb back where it belonged... where it was before to mess with it.

Example: If a bike is running OK, then put up for some time, then on re-start has performance issues, don't assume that the carbs went out of sync sitting in the garage.

 

When I've taken my carbs off for cleaning, it looked like all the throttle plates were closed at idle. Doesn't the air/fuel mixture at idle come through air bleeds? I use the old Carb Stix with mercury for syncing. Some states already ban the use of mercury syncronizers and several more are banning them on in July.

 

A sync work with feeler gauges, or just compare the width of light stream under the throttle blades, will get you vey close to optimal sync. The main reason to use a meter is that you can do the sync with carbs in place and get optimal sync (at about 1000 rpm...). If there is any faulty intake rubbers, leaking intake valves etc, that can not be synced out with a meter or any other method anyway. I use a Morgan Carb Tune II myself, and is happy with it, but know that this or any other gauge is not really needed.

 

Why is mercury free better?

Mercury is a fairly poisonous substance. I was told that one teaspoon full, if vaporized in my house, is enough to do in my entire family, but won't swear that's true. There were a great many articles about the birth defects mercury caused in Japan some years back - it was absorbed by fish which were then eaten by pregannt women. It will also damage the neurological system in children and adults in fairly small quantities. Nasty stuff. I'd go with carb synchronisers that use the metal rods.