Why does TBS help with engine vibs?

[RadioHowie]

Just remember... a TBS doesn't do anything. And enjoy your new bike.

Whoa, there, Fred....don't be gettin' all smug on us now. A TBS is STILL voodoo for vibes at 4k-5k. Auron didn't do a TBS...

He did a "RDCUATBS" according to his post:

We found the throttle bodies to be quite a bit out of sync, my Dad was amazed to find only 1/10th of a turn on the linkages leveled them out.

A TBS and a RDCUATBS are two entirely different maintenance/adjustment animals.

Take credit for perfecting a throttle plate sync (you deserve it), but don't pretend a lowly, bog-standard air-screw adjustment is gonna perform miracles getting rid of cruise-RPM vibes.

 

[Auron]

Oh for sure, technically the TBS only smoothed out the idle, but yes the throttle plate sync is what rocks my world.

This has to be the reason there is such a variation in FJR smoothness. My dad reckons he could get it even closer next time.

 

[Fred W]

A sidenote to this discussion is the effect of the flow orifices on the column heights. I use the four column mercury balancer with flow orifices in each hose. Each column, hose, and orifice is supposedly identical. Yet, when I tee them all together and connect to one of the TB ports the column heights aren't equal -- there is variation between columns, not a lot but it's there and it's repeatable.

Theoretically, the orifice diameter should not effect the average column height, only the amount of "pulsing" up and down that occurs, since the mercury blocks any actual vacuum air flow. Why you observe a difference should not be caused by the orifices. You may have some tiny vacuum leaks somewhere else in the system.

I guess I have been guilty of the "Well MY bike doesn't do that so it must not really happen" syndrome. It is fairly common, not just here but on every forum I have ever seen. Dad's '07 has always been silky smooth at every speed above idle. Once I installed the PC-V it got smooth everywhere. Therefore I ASSUMED...

Some people also say they do not feel the lean surge that occurs in (almost) every fuel injected motorcycle (and many late model carby ones too) at a steady cruise. That doesn't mean that the surge isn't there, or that it can't be improved on, just that they can't feel it.

This vibration thing is the same kind of thing. Based on my own experience, I find it very hard to believe that there is any FJR that could run for years and years without ever needing to have the throttle bodies adjusted, or that if you did adjust them this way that the vibration wouldn't be reduced. OTOH, the need to balance them is based solely on the amount of vibration you feel. So, if the rider can't feel the vibration then I guess it wouldn't need to be adjusted.

A TBS and a RDCUATBS are two entirely different maintenance/adjustment animals.

Take credit for perfecting a throttle plate sync (you deserve it), but don't pretend a lowly, bog-standard air-screw adjustment is gonna perform miracles getting rid of cruise-RPM vibes.

Meh... just semantics.

They are both procedures for adjusting the throttle body's vacuum balance with the same end goals of reducing engine vibration. The RDCUA is the same basic Unauthorized Adjustment procedure that has been bantered about ad infinitum since the FJR was first released. The original "UA" version just had you watching the vacuum as you cranked the throttle open and then trying to adjust out that misbalance. The only thing I have added is a way to do it at a steady state, without all the revving, by first closing down all 4 air screws and then doing it at (near) idle. I've said many times that adjusting just the air screws is a waste of time (and money if you are paying for it). But there are some people that feel any TBS is a waste of time and not at all necessary. Just read some of the posts above.

I'm not looking to take credit for anything. In fact, the whole concept of doing the RDCUA TBS (with the air screws closed) was the outcome of a conversation here on the forum with another New England member (whose name I forget now and who has long since moved on) from up in Old Town, Maine. It was all his idea. I just did the testing and documenting (and then a whole bunch of successful using) of the procedure.

 

[Auron]

It's all in the eye of the beholder. A rider that puts hundreds of thousands of miles on his motorcycles probably carries a mentality that ignores excessive vibration alltogether. Some dudes are just hardcore. A wuss like myself (that's only done 60,000 since 2002) wasn't willing to put up with any excessive vibration at all.

What I'd like to know is, what makes the FJR's engine unique in that it responds so well to this procedure? Makes me wonder if I should have done it to my other bikes.

 

[Fred W]

It's not (unique). Check some other inline 4 cylinder bike forums.

The only thing that is actually unique about it is that Yamaha says not to adjust the throttle plate linkage.

 

[John d]

It's not (unique). Check some other inline 4 cylinder bike forums.

The only thing that is actually unique about it is that Yamaha says not to adjust the throttle plate linkage.

 

[John d]

+1

My last bike a Kawasaki C10 1000. The unauthorized sync was the factory standard method.

It's not (unique). Check some other inline 4 cylinder bike forums.

The only thing that is actually unique about it is that Yamaha says not to adjust the throttle plate linkage.

 

[Fred W]

+1

My last bike a Kawasaki C10 1000. The unauthorized sync was the factory standard method.

True. I had an '01 (Smurf Blue) but that was also a CV carby bike. So no air bypass screws to fool us with.

But... that bike also suffered from the dreaded lean surge, only rectified by using larger pilot jets.

Same reason, though ... they were trying to pass EPA emissions. Even back then.