I have a Kona Fire Mountain mountain bike. I use it for commuting. Roughly 10,000 km on it.
3 rings in the front, 8 gears in the rear. The gears in the back are newish. The middle ring in the front is newer. The small and big rings are original.
Entry level shimano derailleurs. Front is original, I replaced the rear 2 years ago when it broke in half.
Brand new chain.
When the chain is on any of the small (outer) rear gears and I pedal the chain skips over the rear like crazy. If I pedal slowly with no force it operates okay, but as soon as I apply a force required to accelerate, the chain skips over the rear gears. The teeth look okay. The problem only began when I replaced the old chain with the new chain (same chain, shimano HG50, 6-7-8 speed). I used the same number of links etc.
I have been tuning my own using resources like sheldon brown and parktool with success for over 2 years, but I'm by no means proficient in bicycle maintenance. I do believe my cable slack, and hi-low settings and everything are fine. I tune my bike by flipping it upside down and putting it on the ground with the seat and handlebar ends acting as a tri-pod.
Can the springs in the rear derailleur be weak and allowing slack when the chain's on the small gears to skip?
Do you have any other ideas I can try?
Do you suggest simply taking it to a bike shop?