Synchronized carbs = vibrations

[GrimReaper]

 Well i finally decided to sync the carbs this morning with $5.61 homemade manometer.The carbs were way off.I set the idles at 1000 rpm and now she purrs like a dream.Took her for a spin and i notice the well known vibration around 4500 rpm .The vibe weren't there before.This is not a problem for since i ride around 4000-4200 rpm.
 But the question is still there-Why she started to vibrate.

[Rob Valdez 79 R65]

The throttle cable adjusters on the carb bodies may need to be adjusted.  It sounds like one cylinder is working harder than the other.

[GrimReaper]

 Rob, i adjust them too.The vibe is not bad at all.I just can feel it with my feet.

[Mike V]

When you guys figure out the fix for that hi rpm (4900-5100) vibration please post it. I am in search of some experimentation in the days to come with some ideas.  I'm thinking it may not be a fuel delivery issue (carbs). Maybe so. I would expect these bikes to have some normal vibration with the lack of a large heavy inertia dampner of a flywheel. Maybe I should have had the rods and pistons balanced? Timing maybe?

I'll be retorquing heads, adjusting vavles, setting timing and hooking up the Twin Max in the days to come. I've noticed the vibration to be there with different throttle positions.

[Barry]

The vibe weren't there before.

So what your saying is the vibration only appeared after you balanced the carbs ?

If that's the case check out Duane Ausherman's article on carb balancing where he discusses why vacuum balancing may not be perfect.
 
These vibrations are occurring close to peak torque revs and may be caused by one cylinder producing more power (torque) than the other regardless of vac readings. This may also explain why some say they disappear on a thoroughly run in engine.  

Just a theory.

If you can do it safely I would try adjusting one side slightly while riding through the vibration part of the rev range.


http://w6rec.com/duane/bmw/tuning.htm

[nhmaf]

You may also try to "balance" your carb balancing between getting it right @idle and getting it right at@ 4000 RPM (need a fan to keep engine cool while running @4K sitting in the garage).   There is some bit of vibration in these bikes that I think is impossible to remove, but I do know that on this bike, and on my KAwasaki, that I get smoother highway-speed operation if I balance the carbs at idle, and again @ freeway cruising speeds.   If the balance at idle isn't perfect but close and the high speed balance is good, overall I think the engine runs smoother at the speeds you are most likely to notice vibration at.   This is DEFINITELY the case with my Kawi Concours - which is know to be BUZZY in the 4000-4500 RPM range, where it spends alot of its time (@ 72 MPH).

[GrimReaper]

 The bike sounds great at idle and high RPM and a vibe was only there around 4500.I don't mind it or maybe i was too sensitive after 100+ mile ride

[Mike V]

This vibration bothers me - just too harsh and the biggest problem I have is that it is at that most frequent operating range. The plugs look perfect, the balance is very close, timing is dead on and valves are at 0.004" & 0.008".  My metering rods are at the 3rd setting and I'm seriously thinking of raising them a notch just to see how it affects the higher range operation. My feeling is the mid range flat spot and vibration may be a result of a lean setting. I realize a notch will change the mixture a lot, but I'm suspicious since the published Bing static settings for the mixture screws are 0.5 turns ccw and I'm at nearly 1.25 turns ccw just to get it to run. I'm open for opinions and suggestions.