As far as I know pretty much any coil can have some windings removed to make them "hotter".

Go a step at a time. Start with a full layer of wraps if you need a notable improvement. You may end up going further.

I ended up removing about 2.5 full layers of wraps to get my Slick Chick coils to a balanced state. This ended up with way less power than the hot pop bumper coils I got from PBR. I thought I was going to break something the PBR hot coils were so strong. I was very pleased with the results I got taking the wraps off the original coils for this game. Now to try it on my Outer Space where the pops are the only aspect to my game that aren't performing adequately.

My opinion.
1, Rebuild with new coil sleeve, plunger and yolks. Buff ring till it shines.
2. High Tap
3. 1 and 2 isn't good enough (rare), add a bridge rectifier.

I re-built my Williams Klondike pop bumpers and set the machine to high tap,I wouldn't want them any faster, incredible dribbling at times.

Can we assume this is a game manufactured before March 1972?

If so, I would second the steps suggested by Bonzo 71.

If it was made in March 1972 or later, you may just have a burned out leg on the bridge rectifier. I saw that once with a Williams Swinger as the pops and slings were lethargic when I knew they shouldn't be.

Lee