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Ok, as some of you saw in thread about my gas mileage, one suggestion was to sync my carbs. I attempted to sync them at idle, but then at higher rpms they would be unbalanced. So I decided I would sync them at the RPM I was in most of the time. I chose 4000 rpm. Now, they are balanced at 4000 and is unbalanced at idle. Took the bike out for a test run, and the bike ran great on the highway and local roads. Rough at idle, but I expected that. So I guess my question is, at what rpm did you sync? If you did it at idle did anyone look at the balance at speed. Also, what would cause the imbalance? The boots don't look cracked and I have power throughout the range of rpms.
 

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Ok, as some of you saw in thread about my gas mileage, one suggestion was to sync my carbs. I attempted to sync them at idle, but then at higher rpms they would be unbalanced. So I decided I would sync them at the RPM I was in most of the time. I chose 4000 rpm. Now, they are balanced at 4000 and is unbalanced at idle. Took the bike out for a test run, and the bike ran great on the highway and local roads. Rough at idle, but I expected that. So I guess my question is, at what rpm did you sync? If you did it at idle did anyone look at the balance at speed. Also, what would cause the imbalance? The boots don't look cracked and I have power throughout the range of rpms.


What are you using as a synch tool?



As Shep noted, at or just a smidge above idle, and most definitely "Carbtune" in my garage.



Remember after each adjustment to crack open the throttle to say 2000 rpm or so, then let it settle for your reading.



Good luck,

Rick
 

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I use the very easy TwinMax electronic balancer and do the adjustments at idle (around 1200rpm)
 

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When I contacted John Morgan of Carbtune fame,



http://www.carbtune.co.uk/carbcust5.html



and asked him for the recommendation he said all Carb makers expect the carbs to be balanced at the engine's normal idle speed plus a maximum of 10% with Vacuum operated Carb balancers.The vacuum created at the inlets is so powerful that restrictors must be used.
 

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I'll admit that I am different ... I balance my carbs at 6K. That is closer to the RPM that I ride at the majority of the time. I never get numb hands and I don't have harmonic balance problems going down the road.



Maybe some of the carbs I have had in the past needed a better cleaning (before I owned a ultrasonic cleaner), but I enjoyed the ride more with the balance at the higher RPMs.



I use mercury sticks just because I grew up with them. The Carbtune units are just as good but why spend the money when the mercury sticks work just as well.
 

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I'll admit that I am different ... I balance my carbs at 6K. That is closer to the RPM that I ride at the majority of the time. I never get numb hands and I don't have harmonic balance problems going down the road.



Maybe some of the carbs I have had in the past needed a better cleaning (before I owned a ultrasonic cleaner), but I enjoyed the ride more with the balance at the higher RPMs.



I use mercury sticks just because I grew up with them. The Carbtune units are just as good but why spend the money when the mercury sticks work just as well.




I believe in Dave's method but for those who disagree I say if you have any method for balancing them that it is better than none. There has to be 2 or 3 schools of thinking like for every subject.
 

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Just my thoughts on this but if you sync at idle & you loose the sync at higher rpms would that not indicate a sticky main needle slide.I have had this in the past & polished the slides & the bore they ride in & problem went away.Just a thought.
 

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Just my thoughts on this but if you sync at idle & you loose the sync at higher rpms would that not indicate a sticky main needle slide.I have had this in the past & polished the slides & the bore they ride in & problem went away.Just a thought.


Yes you are correct.Also people who think they have synced for higher revs may not actually have done so.Most vacuum operated sync tools cannot operate at those revolutions/intake velocity and most,"Home Made" carb sync tools are inaccurate to start with.



The only real way to check if things are good at higher revs would be on a,"Dyno" and or take the bike to a competent motorcycle mechanic and get the balance checked.



Also,



http://www.carbtune.co.uk/inst.html
 

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I've seen a few people compare homemade ones to expensive ones, and they were reasonably close.



I haven't used this kind yet, but I will be balancing the carbs fairly soon and will be using this kind of device.
 

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I made a sync tool to dial in my old Kz750 4cyl . I spent more than one day dicking around trying to get it right.Finally I bought a set of vac gauges & within minutes had that thing running sweet,my home made contraption was somewhat close but not accurate.Best money I spent. However I now have aprox 20feet of clear tubing if anyone needs some
 

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I made a sync tool to dial in my old Kz750 4cyl . I spent more than one day dicking around trying to get it right.Finally I bought a set of vac gauges & within minutes had that thing running sweet,my home made contraption was somewhat close but not accurate.Best money I spent. However I now have aprox 20feet of clear tubing if anyone needs some


My Carbtune 2 was one of the best buys I've ever made.Getting the carbs dead on at the correct idle speed + max 10% gives both my bikes an incredible power-train of low down torque and smooth vibration free acceleration which allows for less gear changes especially up and down hills around here.

I like doing things ,"On-The-Cheap" but there are some things worth spending the money on and a good carb sync too is one of them which also pays you back in maintaining fuel economy
 

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I think my Carbtune has almost paid for itself in the beer I get in return for lending it out.




Never had to synchronize/recalibrate it either...bonus feature.
 

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I think my Carbtune has almost paid for itself in the beer I get in return for lending it out.




Never had to synchronize/recalibrate it either...bonus feature.


And if you don't know already it's fully serviceable for cleaning




John(Sean) Morgan has made one of the best engineered pieces of kit ever and is a credit to the automotive industry.
 
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