Topic: synchronizing carbs question

[digiacomo racing]

today i was synchronizing my rebuilt carbs on my 78 550k and carb 1, 2, and 3 were all the same, the gauge read 20. the #4
read 40, and when i adjusted the slider adjuster screw counter clock wise to make the  sync gauge read 20 the RPM shot up to about 4K. i checked the manifold boot by spraying it with WD-40 on it to see if the RPM goes up, nothing happend. any suggestions. 

[bender01]

I think if they all read the same 20. You turn down the idle back to 1200 or so and your done.

[digiacomo racing]

the idle screw is backed all the way off

[bender01]

 Did you bench sync them?  With the idle screw the way it is lower the 4th slide to match the others. They should be barely open. The idle screw then will open them to correct idle. Does the #2 carb have a slide adjustment? If not thats the slide height to shoot for.

[digiacomo racing]

i did bench sync them and every carb does have a slide adjuster. do you think that opening all the sliders  with the idle screw will lower the RPM from 4k to 1200 ?

[digiacomo racing]

 Ok, here is what i did, i suspect that there might be a pice of dirt in one of the air holes. so i took the  carbs off took the   the #4 carb apart and i am going to spray it with brake clean re check the float and try it again. any more advice would be nice.

[mattcb350f]

As you dial in the settings to even up the cylinders the engine starts to run better and thus, usually the rpm increases. If it gets near 2500 then it tends to shoot up on its own as the timing advancer kicks in.

Could be something wrong with the carbs, but that's what it sounds like to me. Have a look at the carbs while there out and give it another go. 

 Matt.

[TwoTired]

Do your carbs say PD on their sides?  Or, are they earlier models?

[digiacomo racing]

actually there off a 76 CB550. i bought them on eBay because i allready had the rebuild kits. i will look for the pd  tomorrow.

[TwoTired]

In the US. the PD carbs were introduced on the 77-78 K3 models.  These carbs do not have a slide height adjustment on #2.
This is why your information stating 78 Cb550 confused me.

The earlier carbs have a slide height adjustment on each carb.

Using drill bits for bench sync keeps the slides from closing fully.  If all the individual adjusters are skewed equally, you can achieve carb sync and even vacuum sync later.  But, the slide travel can be limited by skewed adjusters and not let the slides close down to where the need to be at warm idle, even with the main idle knob back out completely.

You should look inside the carb throats with a flashlight and see if the slides will fully close with the idle knob backed out and the throttle cables disconnected.  If not, then you get to do the re-synch over again.

This is one reason why I don't care for the drill bit method, btw.  I adjust each one until light won't pass at each carb slide (off the bike), then vacuum sync with the running bike.

Cheers,