valve clearances then sync

I'm putting my valve cover back on tonight after getting all my clearances in check, then it's on to a running sync.

I have read in almost every thread that it's useless to sync without getting the valves in spec, but I don't know if I've seen an explanation of why this is.

I'm not questioning the validity of this, I'd just like to know in order better understand the whole process.

So ... why?
Thanks!

 

Valve clearences effct the valve timing( mostly when the valves open and close) which will effect carb sync.

 

Exactly.

(OR you could just take Yamaha's word for it




AND if you take a close look at how YICS works, you'll understand why gettting a precise sync does require blocking the YICS (that swirl is coming from the other three carbs' intake tracts



(Or you could just take Yamaha's word for it.)

 

Actually, you can synch the engine (carbs) with the valves (or other items) out-of-spec, and get the engine "synched", which really means this:

ALL CYLINDERS ARE PRODUCING THE SAME POWER OUTPUT.

That IS the nature of "synching", to equalize to power output across all cylinders, so that one (or more) cylinders are not "fighting" against the others, nor is one cylinder carrying a disproprtionate load than others are........

However, the nature of the process also requires that all cylinders be "tuned down" to the lowest output cylinder........else, how do you ever "equalize" the output across all cylinders?

And THAT'S the rub, and the answer to the why questions....why do I need to adjust the valves first, why do I need to have the carbs cleaned first, etc.................because if you DON'T, then it's very likely that the "lowest output" cylinder is REALLY low on power, and you now have to "down-tune" all the rest of the cylinders to that lowest level.

Setting the valves to spec, making sure the carbs are functioning properly, no vac leaks, etc. are necessary to make sure that the "lowest output" cylinder is as high in output as is possible, so that all of cylinders (and thus the entire engine) can produce as much power (and as smoothly) as possible.

Note that all of the above also neglects the need to adjust valves to spec to eliminate possible wear problems due to out of adjustment valves, and that's just one more great reason to do it!

 

This is basic engine stuff. If your valves are too tight on any engine what happens?

The valves do not seal when they are supposed to, and that screws up the vacuum signal from that cylinder or cylinders. So if the vacuum is not right how could you ever sync carbs to the engine. It's IMPOSSIBLE
Besides the only time a valve cools down is when it's on the valve seat in the head. Less contact the valve will overheat and burn.
So the right valve lash will do two things , help the valves cool down so they last and create the proper vacuum signal for the intake system to work properly.
Hope that helps

 

Wow. Thanks guys!
very informative. case closed.