How do carbs go out of sync?

Hi all,

I just did an on-bike sync of my carbs for the first time this weekend. Three intakes were in the 18-20 range while #2 was up at maybe 32 or so. So I lowered that down and the biked started idling more smoothly. But I was wondering how #2 got so high, assuming they were synched before. What causes carbs to go out of sync?

Also, is bench synching more stable? Does it stay set properly as long as the carbs stay on the bike?

Thanks.

I've wondered this as well.

I can see if something were to loosen up, but under normal conditions, if everything stayed tight, there should be no problems.

The only thing i can think of is when you run the engine there is some type of wear that is going to occur ie:valve adjustment,piston ring wear,gaskets and rubber drying up(intake boots) after sitting over the winter.These all have an effect on engine vaccum which is what you are checking when you sync the carbs

Damned if I know. Good question. My guess is that vibration and the slides going up and down in each carb slowly loosens things up. I asked about using some type of sealent to set the nut in position last year or so, hoping that the works would stay put. I think someone mentioned nail polish or somesuch, I didn't bother trying. Although, the first time that I took the top caps off my carbs I saw some type of brownish sealant as a small blob on the nut/threaded bolt shaft. I'm slowly learning a few things, but some days I still need both hands to find my own ass.:woohoo:

OK, I guess engine wear or valve changes might have some effect.. maybe exhaust leaks or changes in backpressure as well?