Change gear problem

[s970022]

I am using Shimano 2-spd crank and 9-spd cassette for my bike. When I change the front gear from H to L, accassionaly the chain drop in the gap of 2 gears. Because the gap of the 2 gears is not big enough to fit in the chain, the chain is just hanging by the L gear but not get into it. I have tried to release the L screw a bit to make the derailer move a little bit more inward when changing gear. However when I put the chain to the smaller gear of the rear, the chain will rub the outer side of front derailer. Is there anything I can fix the problem?
The other problem is when I push once the shifter (road bike shifter) very hard, the chain will jump 2 gears on the rear. Can I limit the deepness of the shifter to avoid the jumping happen?

[cyclerUK]

With the 2 speed chainset it should be a matter of getting the correct adjustments on the H & L screws. Check that there is only a small clearance between derailleur cage and the top of the teeth on the big ring.<br />
With the problem of the chain catching the derailleur make sure it is parrallel to the rings.<br />
See:- http://www.parktool.com/repair/readhowto.asp?id=75
With Shimano road rear shifters they are designed to move up to 3 gears with one hard push!<br />
You will have to learn to be easier on the push as there is no way of limiting them.

[DaveM]

Depending on your shifter, your front shifter may have a "trim adjustment" meaning that you can move the fr derail a little to stop the chain rubbing when you're in the small cog in the back.
Also, check your chain for "stretch". I've foudn this happens more on an old chain.

[s970022]

I just did a quick check and find the issue. When the chain is in the small cog in the rear, the chain will drop in the gap when I change the front deraileur from big to small chainring. But when the chain is in the middle or large cog, the chain drop properly into the small chainring. I think the problem is when it is in the small cog, actually the chain a little bit lean outward which drag the chain into the gap when I change.

[DaveM]

Ideally, the chain should never do this regardless. But, it is generally a better idea to avoid the small to small and big to big gear combinations anyway. In those combos, you end up in a mid range gear that can be achieved with other combinations and the chain is running from the extreme inside to the extreme outside which puts more stress on it.
"It hurts when I raise my arm like this - don't raise your arm"<br />
I'm not a big fan of this type of "cure". But at least if you can't fix the problem, you generally should avoid that gear combination anyway.