Help me understand my 300 XS

[Motv18]

The .44 gap is a hot rod trick to get a hotter spark. More gap more resistance more voltage. I’ve never seen a American bulletin since merc says they are 87 up to e10% safe the .32 gap is fine for that. People recommend with most places only having hard to burn at stock compression 91 ethanol free that the gap and hotter spark to burn it. What you eventually run into is coil voltage recovery as they aren’t designed to deliver that much spark at max rpm. But only later in the coils life. The main issue is prop. Even a 300 will need to down pitch when 1500lbs is added to the boat.

[swaddict]

The .44 gap is a hot rod trick to get a hotter spark. More gap more resistance more voltage. I’ve never seen a American bulletin since merc says they are 87 up to e10% safe the .32 gap is fine for that. People recommend with most places only having hard to burn at stock compression 91 ethanol free that the gap and hotter spark to burn it. What you eventually run into is coil voltage recovery as they aren’t designed to deliver that much spark at max rpm. But only later in the coils life. The main issue is prop. Even a 300 will need to down pitch when 1500lbs is added to the boat.

that makes sense. I'm trying to get a Rev 4 17p to test

[swaddict]

got an answer about the .044 spark plug gap from Don at BBC forums. There was no Mercury service bulletin for the new gap, it was taught in the Mercury Technical Training Classes

[swaddict]

Update, solved the Smartcraft problem. Replaced the trim sender and gauge works perfectly. I also rebuilt the fuel pump and the boat planed very well. I will update when I get the new prop to test.

[Kcraft]

got an answer about the .044 spark plug gap from Don at BBC forums. There was no Mercury service bulletin for the new gap, it was taught in the Mercury Technical Training Classes

…bulletin or not, the little secret is out...

[XstreamVking]

I bumped the gap about a year ago on my optis....They run better at idle.

[Tango]

I have four Opti motors... two were set at .032 and the plugs were wet, corroded and fouled with carbon & oil. The other two sets of plugs were at .042-.044" gap and they were MUCH cleaner. This was done on a boat that has extended trolling and idling for offshore fishing.

[rocketman6965]

^^^^^this^^^^^

[Tango]

But wait... There's more!

This is on my 2004 250XS Alodine block... You know, the ones with the good heads and programming that required 91+ octane. Yeah, right on the sticker it says .040" gap.

So let's move on to the 2010 250XS and check it out... .042" gap.

Looking at these, I'd never go with .032"