Dudes...my fuel servo hadn't been touched in 25 years. I had a burp on run up (with 12 inch flames coming out my exhaust), I had fluctuating fuel pressure in climbs, fuels smells when leaning...and was flying 140kts at 25/2500.  So, I replaced it. No burp. No fluctuations. No more smell. AND HOLY SHIT, I make 153 KTAS now at 25.5/2450. I can't believe what a difference it makes when the engine in getting the right amount of fuel in a consistent way.