What causes the tachometer RPMs to "surge" higher when changing gears
from 2 to 3 while depressing the gas pedal?

Doesn't happen all the time.

On 14 Apr 2007 09:59:30 -0700, "angusbn (AT) gmail (DOT) com" <angusbn (AT) gmail (DOT) com>
wrote:

the tach to jump every time I do it. It does this in my car, my truck
and my tractor. I think there is something wrong with the clutch pedal
on all 3 contraptions. It would do it on my motorcycle if I owned one.
But the motorcyle does not traditionally come with a throttle pedal.
Two of the three vehicles I own now don't have gas pedals either. The
do have throttle pedals but they are deisels so it is hard to have a
gas pedal if your vehicle does not use gas.

angusbn (AT) gmail (DOT) com wrote:
There is a damper on the throttle. It's a little assembly with a
diaphram and an orifice that bleeds down at a designed rate to prevent
the throttle from closing quickly. When you take your foot off the gas
it prevents the throttle from closing instantly to reduce emissions. If
the orifice is clogged it can become slow and cause what you describe.
(Sometimes it's designed such that it causes what you describe even when
working correctly.)

HTH.

JRE