The return on yours seems slower than it should be. The other video is of a spare stock set of 98 600f3 that I have. The return on them is on the money.

Yours, while they are slower, they are consistent. #4 might be a little slower but I can't tell.

This area is pretty easy to troubleshoot. Assuming the diaphragm are good and the springs are the correct ones, there really isn't that much left.

One thing to double check. Are you positive that the needles are seating in the correct passages? On the f3's its possible to send them down the wrong hole

 

The videos I've seen of carbs with vacuum issues have all centered on the diaphragms leaking due to tears or being pinched when assembled (made obvious by the instant closing of the slides). Mine are definitely slower than the F3's in the video, but they clearly are not leaking. I don't know enough to know if they can be too slow (I guess that would be obvious in throttle response under load.... which I'd love to be able to test! The one thing I was wondering is if their age had stiffened the rubber (definitely the case with the carb boots), slowing their response. Not sure what to do if that's the case as they're only available used and would be of similar vintage (as far as I know).

With respect to the needles, there is only one place they can go. In fact, I can view the ends of the needles when they're seated by removing the main jet. They fit perfectly, are perfectly clean/straight, and do not bind at all when operated by hand... to my untrained eye, perfect. Post resurrection, I'm not sure the engine has ever been at an RPM level or load to even give them a chance to operate yet. The few times the throttle did respond, they'd just shudder a bit.

 

Hi , are your carbs on or off the bike?

 

On at the moment, but I've gotten pretty fast at removing and replacing them.

 

I'm sure you have , any thoughts about trying them on the bench ,using the Auxiliary tank to run fuel into the carbs and see how much they leak, there is also a test that you can do to test the height of the floats without taking the bowls off, its usind a length of clear tube , attaching it to the bowl drain outlet ,holding the clear tube to the side of the bowl where you would have taken your measurement, and see how high the petrol comes up the clear pipe ( holding it fixed to the side of the carb), there should be a video somewhere to show you better than I can explain it

 

Thanks for the video. I had read able that technique, but never tried it for lack of insight as to what I'd do with the info (I don't know what a good vs bad float bowl fuel level is.) In hindsight, it may have revealed if it was too low. I know they were filling to some extend because I'd drain them before removing the float bowl, and there seemed to be significant fuel in each.

I did ponder bench testing, but couldn't think of any tests that I thought might reveal anything useful. The only 'on the bench' thing I've done was to connect a small shop-vac to the intake manifold side of a carb, slowly open the throttle, and see what the vacuum slide did (it lifted about 1/2 way). That told me they worked although I had no frame of reference of the vacuum level created by the engine vs. shop-vac. I didn't know if 1/2 way open was good or bad.

The leak test is a good idea which I may perform if my inquiries for local mechanics comes to naught.

 

Hi , I was thinking if you could place the carbs in a bowl (to collect any overflow) in an upright position as they would sit on the bike, connect the auxiliary tank turn fuel on , just to see if they leak, with only gravity feed the floats should be able to seat the float needles , if the petrol still runs through then the float needles are not closing, therefore letting fuel past,

 

Hi,
I posted in a local riders forums asking for suggestions for bike mechanics and a guy ftom a local shop suggested I call him so I did. After explaining the things I've done, he said he thought there may still be clogged passages or have coated surfaces, and that they really need to be ultrasonically cleaned. So I think I'm going to get a cleaner and try that. He also suggested what you did... test float bowl fuel level with clear tubing. I'll probably try the leak test as you've described as well after they're back together.
And if all that doesn't improve things, I'll just bring it to them to fix.

 

Yes the Ultrasonic cleaning is good, lost count of the times I've had carbs on and off because I've left minute particles in there

 

It certainly won't hurt anything. Plus your carbs will come out smelling fresh. :-)
I have one and it does help to get all the tiny holes and passageways clear.