Carb synch issue

[racerboy]

Happy new yr everyone,
I have an 07, carbs all clean, nice and tight, the only problem, carbs 1,2,3 synch beautifully, #4 is off. no matter what I do, it will not line up with the rest. I even swapped out the vac. lines between 3 and 4 just to see if #3 displays what 4 showed. it did.
Air mix is good, no leaks, in fact, it revs as it should, no stumbling or rev trickling down slowly. New plugs, good fuel, Im using the alpha moto dials, the needles are lined up on Zero in the white. The only thing I have not done is a test ride and plug read. thats next. Any thoughts?

 

[desert_max]

Sometimes there’s a little slop in the linkage. Are you blipping the throttle between adjustments to ensure that it settles back down?

 

[Fire-medic]

I know that you said, "no leaks," but I'd be checking the rubber donuts for leaks, clamp tightness, and the O-ring on the VBoost to cyl head connection, spraying starting fluid on the joint, for that cyl.



If you don't find anything there, I think I'd be back-into the carbs. Check if the CV diaphragm is positioned properly, that it has no holes, and that the jet block in the carb has its round rubber plugs, and that the pilot jet is clear and screwed-in. I once got a bike that had the rubber plug properly-installed, but the pilot jet was unscrewed, and rattling around inside the jet block.

 

[maleko89]

I know that you said, "no leaks," but I'd be checking the rubber donuts for leaks, clamp tightness, and the O-ring on the VBoost to cyl head connection, spraying starting fluid on the joint, for that cyl.

View attachment 81958

If you don't find anything there, I think I'd be back-into the carbs. Check if the CV diaphragm is positioned properly, that it has no holes, and that the jet block in the carb has its round rubber plugs, and that the pilot jet is clear and screwed-in. I once got a bike that had the rubber plug properly-installed, but the pilot jet was unscrewed, and rattling around inside the jet block.

Check that the emulsion tube is tightly secure and Choke plungers are fully in. The choke linkages can be hokey too.

 

[Stephan]

If the air and fuel system checks mentioned above do not reveal a fault, then what actually happens when you synch the carbs is that you are ensuring that the brass discs in the carb intakes are all in the same position on their throttle shafts. It may be useful to remove the airbox and have a look at the brass discs to see if #4 is visually different - although the difference could be very small you may be able to see it. You could also inspect the screws, springs and stopper plates (the screws bear on the stopper plates) on the throttle shafts to see if anything appears wrong/different. For example if your #4 stopper plate is bent then you may have run out of adjustment. You should also be able to see the extent to which the springs are compressed. Is #4 compressed more or less than the others? If so why? If all appears normal you could try backing off all the screws and starting from scratch.

 

[Parminio]

Happy new yr everyone,
I have an 07, carbs all clean, nice and tight, the only problem, carbs 1,2,3 synch beautifully, #4 is off. no matter what I do, it will not line up with the rest. I even swapped out the vac. lines between 3 and 4 just to see if #3 displays what 4 showed. it did.
Air mix is good, no leaks, in fact, it revs as it should, no stumbling or rev trickling down slowly. New plugs, good fuel, Im using the alpha moto dials, the needles are lined up on Zero in the white. The only thing I have not done is a test ride and plug read. thats next. Any thoughts?

Don't get offended, but are you sure you're doing it right?

There is one screw on the left "drivers side" for carbs 1 & 2. There are two screws on the right "passengers" side for 3 and 4.

Increase your idle thumb screw to get the idle up to at or just above 1,000 rpm. Make sure your choke is completely off.

You set the 1 & 2 screw first to get them to be the same.

Then you set the REAR ONLY screw on the right side so that 3 & 4 match. Don't even touch the front screw at all until you get that done.

Then you adjust the front screw to tune 3 & 4 to be the same as 1 & 2.

I've seen people start messing with that front screw first and get it into a position where they are never able to get #3 into sync.

 

[02GF74]

 

[sdt354]

I've been messed up from a stripped sync screw before. Twice I'm ashamed to say. The second time not as long to figure it out. Turning the sync screw and nothing happened. It's easy to miss. Make sure the screw moves the linkage.

 

[racerboy]

no offense at all, Ive done this in the past on my last Vmax (92) never had problems. But. alas, I will heed your steps and try that. thxs

 

[racerboy]

Well, Saw this old thread and finally!! solved the issue. the jet block? the gasket under it? totally dissolved, did not notice any debris in the bowl nor any indications of deteriorated material, my thoughts there, just melded with the fuel, out the exhaust. Oh, carbs one and two. Chkd the others, replaced them to be safe.

 

[02GF74]

The gasket should not dissolve, is it possible they were not fitted?

You did the correct thing in replacing the others whilst the carbs were off (removing and refitting the is a right PITA).

 

[maleko89]

Agree. I’ve seen some bad ones and worst was like brittle.

 

[Fire-medic]

The all-in-one carb kits give all sorts of problems. Poorly-fitting brass, incorrect sized orifices, gaskets which swell-up when in-contact w/gasoline, you name it. Maybe a former owner did the re-build and as 02GF74 mentioned, they forgot to install the jet block gasket. How tight were the jet block phillips screws (yes JIS screws)? If the gasket was there, but 'dissolved,' I'd think that the screws would have been loose upon your disassembly. If the screws were tight/snug, then the former person 'in-there' made a bone-headed error and he forgot to install the gasket.