What's My TBS Move?

[Patent1]

Attempting a throttle body sync on a 2005 Gen I.  Turns out cylnders 1-3 are pretty close, but cylinder 4 is pulling much less vacuum, and its air adjustment screw is bottomed.  I see two alternatives: 

A.    Use cylinder 4 as my reference cylinder, and sync cylinders 1-3 off cylinder 4,  or

B.    Adjust cylinder 4's mechanical linkage adjustment screw to hopefully increase its vacuum, and sync the cylinders using cylinder 3 as my reference, as Mother Yamaha intended.

Leaning to Option B.  Do you folks agree?  Any other suggestions?

 

[RossKean]

Doesn't really matter.  When things get "off" so I can't sync or can't get idle adjusted properly (Gen II), I start by screwing in all four until lightly seated and then open each about 3/4 of a turn and I start from there.  I haven't done it but you might want to have a look at Fred W's thread on TBS.



It includes a link to a downloadable Dropbox file.

Good luck.

 

[Fred W]

So, if cylinder 4 has less (lower) vacuum, that means cylinder 4 is drawing more air (not less).  That means it can’t be a blocked air port on 4.  It could be the other three are getting plugged up, or maybe the throttle plates on the other three are cruddy.

I would try closing all 4 air screws completely to see where everything else is.  You could adjust the throttle plate linkages at idle to get them close, and then see what happens to vacuum as the throttles open. If they vary a lot as you open them then they may be dirty.
 

On my old ‘05 I took the throttle bodies off for cleaning at around 75k miles and they were pretty well crudded up.  Cruddy throttle plates will affect things at idle more since they are only cracked open, so any deposits represent a greater proportion of the air passage.  
 

Hope that is helpful.
 

 

[escapefjrtist]

So we have more information, how many (s)miles are on the '05?

From previous PNW Tech Days, we've run across a couple older FJRs where the idle adjustment and air screws end up at the (opposite) extremes of adjustment. You either end up with a low idle or can't get a good TBS. What's the idle speed? Can it be adjusted normally?

~G

 

[Patent1]

Thanks all of you.  I should have mentioned the bike has 51 K miles, and the throttle bodies are clean.  I just replaced the starter, which required removal of the throttle body assembly.   Cleaned the throttle bodies before re-assembling the bike.  The TBS sync was the last job before I planned to button her up.

  She idles at approx. 1500-1700 when warm (2-3 bars on temperature gauge.)   I have rotated the idle adjustment knob counterclockwise with no effect.   I'm afraid I may have shortened/tightened the throttle cables when reattaching them to the throttle body assembly.   Yet the throttle seems to have the normal play. 

At this point, I'm thinking I should just open her up again, and confirm the throttle cables have the correct play.  I'll worry about the TBS sync once the bike is idling at 1050 rpm.

 

[Fred W]

Before you do that, see what the idle is when you close all the air screws.  It should be very low at that point.  The air that passes through the air screw passages in the TB make up a significant percentage of total intake air at idle.  If you just cleaned up the throttle bodies, you just might need to close down the air screws some to get the idle speed down.

 

[Patent1]

Thanks Fred.  I'll try that and report back.  Don't hold your breath,  as we are going to Atlanta to visit my brother and his family.  No chance of playing with the bike until after we return.

Jim

 

[RossKean]

 If you just cleaned up the throttle bodies, you just might need to close down the air screws some to get the idle speed down.

That idle speed is way high!  That's why I do a "reality check" by starting out with everything a bit less than 3/4 turns out from lightly seated - especially if it has been a while or if I have done major maintenance.  Inability to balance suggests that something is amiss.

Since you just had everything apart and back together, have a really good look for leaks and/or a hose that didn't get hooked up.  Any difficulty getting the big couplers to the throttle bodies properly sealed?

 

[escapefjrtist]

That high idle is the clue something is wrong. Since you had the throttle-bodies out, start with the simple stuff and double-check your work.

~G