TBS screw travel

Hi all. Did my 4th TBS today and ran into a small snag. The adjustment screw for cylinder [EDIT:] #2 is currently all the way in/reached the end of its travel. The vacuum pressure was something like 245 mm Hg, so I left it at that and synced the rest of the cylinders to #3 (using a new Morgan Carbtune: it is so much easier to use than my old mercury-filled manometer). During the next TBS, can I simply lightly seat all the screws and back them out 1 or 2 turns to "reset" the adjustment travel available? Will it throw the pressure out of whack so much that I'll end up near the end of the screw's travel again?

Thanks in advance.

Huh?

There are about a "jillion" answers in Google: tbs site:fjrforum.com

Basically...get them even. If you "have" to back them off to get travel....

otrfjr said:

The adjustment screw for cylinder #3 is currently all the way in/reached the end of its travel.

Click to expand...

I thought #3 was supposed to be left alone and 1, 2 and 4 were to be adjusted to be the same as #3.

It sounds like the adjustment screws that are never supposed to be touched....LOL.....on the throttle body linkage have gotten out of whack somehow. The air screws used for the normal TBS have a pretty limited range as they only control "bypass air" around the throttle blades. The throttle blade position may need to be synced using the adjustments on the linkage. In short, you would want to set all the idle bypass air screws to the same setting (either bottomed lightly or out 1/4 turn or out 1/2 turn....whatever blows your skirt up) and then adjust to the same vacuum levels using the linkage adjustments....that would be the screw arrangements on the connection of the throttle shafts between each throttle body. That is the simple story. Much more complex ones are available.

Or......

You may just want to forget the absolute vaccum level, adjust #3 to 1/2 turn and try syncing the other throttle bodies to it as required. If the RPM gets too high or the vaccum is too low adjust the main idle speed knob to bring all cylinders back down (or up as required) and keep syncing with the air screws.

Joe2Lmaker said:

otrfjr said:

The adjustment screw for cylinder #3 is currently all the way in/reached the end of its travel.

Click to expand...

I thought #3 was supposed to be left alone and 1, 2 and 4 were to be adjusted to be the same as #3.

Click to expand...

+1.. That is my understanding too!! I never mess with the #3 setting.

WW

Thanks Jestal. I'll try option #2.

jestal said:

It sounds like the adjustment screws that are never supposed to be touched....LOL.....on the throttle body linkage have gotten out of whack somehow. The air screws used for the normal TBS have a pretty limited range as they only control "bypass air" around the throttle blades. The throttle blade position may need to be synced using the adjustments on the linkage. In short, you would want to set all the idle bypass air screws to the same setting (either bottomed lightly or out 1/4 turn or out 1/2 turn....whatever blows your skirt up) and then adjust to the same vacuum levels using the linkage adjustments....that would be the screw arrangements on the connection of the throttle shafts between each throttle body. That is the simple story. Much more complex ones are available.

Or......

You may just want to forget the absolute vaccum level, adjust #3 to 1/2 turn and try syncing the other throttle bodies to it as required. If the RPM gets too high or the vaccum is too low adjust the main idle speed knob to bring all cylinders back down (or up as required) and keep syncing with the air screws.

Click to expand...

Joe2Lmaker said:

otrfjr said:

The adjustment screw for cylinder #3 is currently all the way in/reached the end of its travel.

Click to expand...

I thought #3 was supposed to be left alone and 1, 2 and 4 were to be adjusted to be the same as #3.

Click to expand...

#3 is supposed to be set to 250mm Hg (9.8 in. Hg) at 1100 rpm idle.

then the others are supposed to be balanced with that.

when done, reset idle speed to 1100 and make sure vacuum is still at 250mm.

Fred W said:

Joe2Lmaker said:

otrfjr said:

The adjustment screw for cylinder #3 is currently all the way in/reached the end of its travel.

Click to expand...

I thought #3 was supposed to be left alone and 1, 2 and 4 were to be adjusted to be the same as #3.

Click to expand...

#3 is supposed to be set to 250mm Hg (9.8 in. Hg) at 1100 rpm idle.

then the others are supposed to be balanced with that.

when done, reset idle speed to 1100 and make sure vacuum is still at 250mm.

Click to expand...

At sea level. Have yet to find a cave in Minnesota deep enough to satisfy Yammis demand for 250hg, so I have settled for even balance on all four, rather than some ambiguous figure in the manual, and somehow, Frank is still my pal. And, as jestal hinted at, don't [SIZE=24pt]EVER[/SIZE] touch the 3 synch screws on the throttle shaft, or bad juju be gettin' yu mon!!!!!!

More Synch Info Than You Can Ever Read

#3 is supposed to be set to 250mm Hg (9.8 in. Hg) at 1100 rpm idle.then the others are supposed to be balanced with that.

when done, reset idle speed to 1100 and make sure vacuum is still at 250mm.

Click to expand...

I would highly recommend that the idle be adjusted as the TBs are adjusted so that idle always remains at your target speed (1,100 rpm). It helps you get an accurate TBS when all the TBs are adjusted at the same engine speed, and it reduces the tendency of the TBS screw to either bottom or top out. It isn't uncommon for people to complain that after a TBS they can't get the idle screw to travel far enough to set idle speed where it should be, adjusting idle during the TBS will help prevent this too. IMO, YMMV.

radman said:

And, as jestal hinted at, don't [SIZE=24pt]EVER[/SIZE] touch the 3 synch screws on the throttle shaft, or bad juju be gettin' yu mon!!!!!!

Click to expand...

Nah. It's not rocket science here.

The key here is that the shaft screws would only be adjusted very slightly if there is vacuum mis-balance at a partly open throttle. Then you'd want to go back and recheck the idle sync. Here' what I've done:

1) Set idle to 1100

2) Adjust #3 air screw using a single vacuum dial gauge to 9.8" (now don't touch this screw again)

3) using TwinMax, balance #3 to #4 with #4's airscrew.

4) open the throttle enough to raise the rpm to ~3000-4000 and watch that the vacuum remains balanced. If not, this is where you would adjust the connector between #3 and #4. You want the throttle plates only open a crack because that is when the manifold vacuum is the highest and any variation in the plates position will be most evident.

5) Reset idle to 1100 if necessary.

6) Readjust the airscrew for #4 for balance at idle if the linkage was touched.

Then repeat steps 3 - 6 comparing #3 with #2, and then #3 with #1.

Final step is to reset idle and recheck #3 for 9.8". It should still be and you should be done.

I was being, ummmmm, sarcastic......... Read the link.

radman said:

I was being, ummmmm, sarcastic......... Read the link.

Click to expand...

Not only is FredW from New Hampshire he is also an engineering type. We are immune to subtlety, mirth and romance. Please be explicit, direct and include footnotes and a bibliography with your posts. :lol:

ionbeam said:

radman said:

I was being, ummmmm, sarcastic......... Read the link.

Click to expand...

Not only is FredW from New Hampshire he is also an engineering type. We are immune to subtlety, mirth and romance. Please be explicit, direct and include footnotes and a bibliography with your posts. :lol:

Click to expand...

damn... you're onto me.

(I think he snuck that link in after the fact, cause I sure the heck didn't see it before.)

My 20 yr old Manometer, with glass tubes glued on a Hot Wheels track in a piece of PVC has no MM markings. I feel so ashamed.

Fred W said:

ionbeam said:

radman said:

I was being, ummmmm, sarcastic......... Read the link.

Click to expand...

Not only is FredW from New Hampshire he is also an engineering type. We are immune to subtlety, mirth and romance. Please be explicit, direct and include footnotes and a bibliography with your posts. :lol:

Click to expand...

damn... you're onto me.

(I think he snuck that link in after the fact, cause I sure the heck didn't see it before.)

Click to expand...

Naw, I wouldn't do that.........

Powerman said:

My 20 yr old Manometer, with glass tubes glued on a Hot Wheels track in a piece of PVC has no MM markings. I feel so ashamed.

Click to expand...

Neither does my twinmax. It still does the deed.

When I was experimenting with various TB syncing techniques I noticed that the fully closed position on each TB air screw is not the same for all TB's. The closed rotary orientation (slot) of the air screws differs a bit. Three were almost identical when fully closed but one (#4) was quite a bit different. Coincidentally or not that one "different" air screw is the one which always needs the most adjustment during each sync. #1 & 2 never require any significant adjustment.

It would seem that all would be almost identical since the screw threads are identical. Maybe the tip of the #4 screw has an imperfection which doesn't mesh perfectly with the TB. Maybe there's an imperfection inside the TB where the tip of the air screw comes to rest.

I'd remove the #4 screw and inspect the needle valve tip but I'm not sure I could reassemble it with no ill effects.

No biggie buddy; just back all of the screws the same amount, say, 1/2 turn, then readjust your idle with the idle screw, which is nothing more than a 'master' air screw (take a close look and you'll see what I mean). When you do that, do leave #3 alone and adjust the others around it, so it's faster. Worst that can happen if you 'mess' with #3 is you either have a too high an idle or too low; easily remedied, since it's a 'closed' system (master/idle screw feeds all 4 TBs). And if you're really careless trying to lower your idle more than you can (could have happened to me, but didn't), you could back out the idle screw all the way, and possibly lose the spring, so DON'T do it. This 'master' screw is not really needed since you can adjust the air screws with it all the way out (mine is like this now), but makes adjusting your idle a snap when individual screws are within adjusting range, rather than having to mess with the individual air screws every time (kudos to Yamaha).

By the way, vacuum depends on your altitude, do don't try to adjust it; just make sure all 4 TBs are as close as possible to each other.

I also left #3 a bit too deep, and my idle can't be lowered more than 1,250, and I want it at 1,200 rpm, so have to go in there and back them out a bit too, which will do at the time I perform another TB synch after break in. By the way, reason I set the individual air screws as deep as possible is my bike restarts to idle speed immediately when hot, rather than restarting around 800, then slowly climbing to proper idle speed (like stock settings). No biggie at all, but the tinkerer in me wanted to make it better, so I experimented. Oh, and I marked all my screws before messing with them, but don't plan to put them back to stock, especially the 'unauthorized' ones, which were far from perfect. Hope this helps, and if you need more help, send me a PM.

JC