vacum hose to petcock

Hi all... quick question... i was starting the bike with the tank vacum tube off. the bike seemed to idle faster, i than attached the vacum hose from the third carb to petcock and the bike would idle down.

What causes this? it seems that the bike is easier to start when the vacum hose isn't attached to the petcock. (took the petcock apart and it is clean and in working condition)

Another qustion:
when i took the carbs apart and put them back together i took the enrichment screws out. i know the manuel says do not play with these as they are set by the factory. What are they supposed to be set at?

Thanks all

 

It idles faster because of the vacuum leaking to atmosphere, not because of anything petcock related, if i'm understanding your question properly.

if you mean the mixture screws, i believe the factory 'default' (at least for the hitachis on my bike) is 3 turns out from bottom.

hope that helps

 

The bike will idle higher because you have the vacuum open to the atmosphere. However, without the hose hooked up to the petcock fuel won't (or at least shouldn't flow to the carbs) Unless you have it set to 'Pri'.

 

Do you know what the physics behind that is? Why would it run faster and than run slower when plugged or attached to the petcock?

Just curious thats all.

thanks

 

Unless you plug the line the engine is now letting air in through the vacuum tube making the engine run lean. Running lean will damage your engine.
Having the tube hooked to the petcock is essentially plugging the tube (it pulls a diaphram in the petcock but does not let air in the tube).

Lean refers to the air/fuel mixture having too much air.