[sdirwin]

I just sorted out the vacuum leak on my 2002 T-Bird with Keihen carbs. Bike now fires rights up, idles smoothly with good throttle response. Quite satisfied with myself, I set about the synch the carbs before Miller time. That’s when my new troubles began.

I’ve synched many carbs, and my usual experience is a few minutes, a few tweaks and all the needles are dead nuts. Not this time. The left carb synched up easily, but I’m having no luck getting the right carb to synch with the middle. It seems when I turn the screw to get the needles close, the idle climbs above 1,000 RPM. When I then back off the main idle adjuster wheel to bring the idle back down the 1,000 RPM, the synch is way off again. It’s very much like over-steering a boat…too much to port, then over-correct to starboard…pretty soon the entire crew is heaving over the rails. You get the picture. Now, I think I have the idle completely out of whack between the right carb screw and the main idle adjuster wheel.
Can someone help steer me back to on course? Should I set the right hand carb screw and idle adjuster at some happy medium to start? Should I turn the right hand carb screw all the way in to start? All the way out? Something in the middle?
Help!
Thanks-
Scott

 

[IrlMike]

I had a problem with my Tbird where the tacho was overeading by ~ 300 rpm. (Quality a bit underwhelming imo.) Result was I couldn't get a synch because the idle could not go down far enough, tho' it wasn't easy to tell. My experience was telling me that the idle was too low but I found it hard to believe the tacho error. Swapped for a trophy clock set off ebay & all was well -easy synch. Only other thing I can think of is just make sure pilot jets are clean, rubbers are good & clamped tight & float heights right.

 

[sdirwin]

Thanks. My tach is working fine. 1,000 RPM idle sounds like a 1,000 RPM idle. Just cleaned the carbs, so that's not it. Rubbers are a possibility. I carefully visually inspected all and made sure everything was tight.

I'm really hoping someone could tell me where I should start with the balance screws. Right now, I have the right screw turned all the way in. Should I start there? All the way out? Somewhere in the middle? Does it even matter where I start?

 

[cafetbird]

Are you following the procedure as it instructs in the service manual, Scott? I have followed that process several times and had good results.

 

[sdirwin]

I'm following the procedure in Haynes, which is the same procedure I've always used.
1. pull vacuum caps
2. put hoses from vacuum gauges on vacuum nubs
3. start bike and warm up to "normal" operating temp
4. set idle a tad higher than 1,000 RPMs
5. center carb is master - synch carb 1 and 3 to master via synchonization screws between carbs
6. blip throttle a few times to make sure carbs settle back down in synch
7. bring idle back down to 1,000 RPMs to make sure carbs settle back down in synch
8. smile
9. ride

I've never had a problem like this where right carb measures double the master. I'm turning the right synch screw so much that it begins to change the idle. Then I turn the idle up and its deja vue all over again.

 

[Sned]

Did you try to swap the hoses on your vacuum gauges from one to three and see if perhaps there wasn't a problem with the gauges causing an anomalous reading? If you have a four cylinder gauge did you try using the unused gauge in place of the one that you can't get balanced?

 

[tbs992000]

The carb that the cable hooks to is the base carb synch off of that one . make shore cable is adjusted and everthing is good first ,plugs,valves,air filter.Do not overheat bike keep fan on to prevent this . Dont get upset if it does sent work the first time walk away take a brake .

 

[Mag00]

First thing you should have done is to write down the settings of your idle adjustment screw and synch screws. What I mean is this: You have a benchmark, a base setting of all the adjustment screws before you start the synch. So, when you set the idle on the base carb (#2 carb) you should have written down how many turns you made to get it to the desired idle speed. Then when you adjusted the right carb(#3), you should have written down how many turns you had to make to get it to synch to the #2 carb. And so on. If you write everything down, you can return to the original settings that existed when you first started your synching and start all over again.

Once at the original settings, you can re-diagnose any problems you may think you have, make corrections, then attempt to re-synch the carbs. But, you didn't say you did that and you said you might have messed up the #3 carb synch, right?

So, stop where you're at and make sure you really did fix all your vacuum leaks. Get some gauges and do some tests. Then, fire it up and set your idle fuel mixture (pilot screws) to optimum settings. Then re-synch. Set idle speed to around 1000 rpm on base carb then synch the other carbs to it according to service manual directions. But write everything down this time. If you turn out the base carb idle screw 1/2 turn, write that down, etc.

Also remember that synching is not a science of exactness. You do not have to have perfectly matched readings between the carbs--just as close as possible where the engine runs smoothly, idle is stable, etc. Also, be prepared to go back and forth between synching #1 and #3 carbs repeatedly, as well as repeatedly adjusting the #2 carb (base carb) idle speed.

I hope this helps a little. I learned the hard way the first time I synched the carbs on my 2000 Yamaha Venture. Now I write everything down and I settle for the best I can get rather than making everything exactly the same.

 

[sdirwin]

OK. I'm starting from scratch. I pulled the carbs off so I could re-set everything on the bench. First, my pilot screws are still sealed from the factory, so they can't (and, most probably, don't need to be) adjusted. I set the main idle adjuster screw (the one with the plastic thumb wheel accessible in situ) so it is just touching the accelerator (and not advancing it). I figure this is the lowest idle setting for the middle/base carb. I noticed when the base carb is set as such, the butterfly is more closed than the other two carbs. So, I screwed in the carb adjuster screws on each of carb #1 and #3 as far in as they would go, which closed their respective butterflies as much as they would close. I figure this (all three butterflies closed to the maximum extent) would be the lowest base idle setting. I could then re-install the carb and start from there. If the bike doesn't start, I would increase the main idle adjuster by 1/4 turns until the bike started. Once it started, I could increase the idle on carbs #1 and #3 by backing off the idle adjuster screws that started screwed all the way in. I would do this with the vacuum guages on the bike so I could monitor/synchronize the relative idle among the 3 carbs.
Is this a sensible approach, or should I do something differently?
Thanks for your help, guys!
Scott

 

[Ballacraine]

That does seem like a very methodical approach, Scott.

At the risk of telling you how to suck eggs....

Whilst you still have the carbs off, obviously you have checked for cleanliness & wear damage?
Whip the float bowls off & check for any contamination, if you haven't already. Check your float height whilst you are there.

Check the air filtration as well.

I would then proceed as you wrote. It is important to start from a known point.

Vacuum gauges can be misleading. I would suggest considering a Twinmax. Do a google on it. It is basically a DP cell based unit.
It works off the differential in pressure about a diaphragm. It has variable sensitivity & can be tuned very accurately and easily.

Nige.

 

[Mag00]

You should be okay Scott with the way you are doing things. And you're right, don't touch your pilot screws unless you absolutely have to. And you shouldn't have to unless your carbs need to be cleaned and/or rebuilt. If you manage to get carbs bench-synched before reinstalling them on your motorcycle, that should ease your starting woes should you have any.