Tuning a V-6 Merc suggestions

[Jay Smith]

I cut HUNDREDS of heads and on most healthy 2.5 with stock porting most at 34 CC's with a 1 MM head gasket at sea level will yield 140 -145 lbs cranking, I find that to be a safe compression using pump gas premium. Pryo's as a tuning tool are fine but can sometimes steer you wrong. Remember at 10,000 RPM's a Mercury piston speed is near 120 times a second and IF the user feels they can "catch" a lean condition before the piston failure occurs is living a pipe dream. Even the quickest digital EGT's when they resgiture a spike your motor blew up 10,000 cycles ago if it hasn't already locked up , I find a "tuned ear" can s reduce some of the carnage by listening to the engine carefully. EGT gauges also coke up and become insulated and give a false reading. Also I get a kick out of those that tell me their "seeing" 1400 + degrees on a EGT gauge, well folks most forged pistons would be a melted pile of GOO at 1400 so that is proof that gauge reading is a bunch of HOOIE..

This is a suggestion I have shared on ALL forums, I've passed this info along for 15 years and its NEVER failed me yet about the "jetting" subject:

When tuning I start with a known RICH condition, I make a hard pass with a set of new plugs installed and if safety allows kill the motor clean at top rpm. Remove the #5 plug and roll to BDC ( bottom dead center ) with a dark towel over the power head and my head to block all sun light I inset a bendo lite in the plug hole, look of the intake wash side of the piston and observe the intake wash wetness, if the piston crown is wet half way across the piston its very rich, if its the size of a quarter ( coin ) its very safe, if its the size of a nickel is just about correct if any less than that your running a bit lean you need more fuel and if its dry your lucky that pass didn't get a piston , remember ALWAYS start rich and work down never the other way you might not get a chance to richen BEFORE the piston burns..

Always makes me feel good when I read in print one of MY suggestions I've reported on for years to be successful and folks are passing the info on year after year ....

Good luck,
Jay