Piston burn pattern?

**RWN50** · 05-27-2015

Could anyone tell me what their thoughts are on the burn deposits on the crown of my pistons. i know its far from ideal but id like to know whats causing it.

50D2 tohatsu
30psi more than stock compression
reeds
exhaust
standard jetting 132 132 135
revving 1400rpm harder than OEM limiter
50:1 with 98ron

**Fast Fred** · 05-27-2015

looks like the 132's are lean, the 135 is better but still lean, 138's or 140's for all

**RWN50** · 05-27-2015

How much power will i be losing by richening it up? i have never heard of anyone running more than 135s on a mod tohatsu anywhere in the world.

**Fast Fred** · 05-27-2015

not a lot of color on the crowns, how do your plugs look, what made you pull the head

**champ20B** · 05-27-2015

If the plugs are real clean after an hour or so running, could be moisture (water) in fuel or from somewhere within.

**RWN50** · 05-27-2015

Fred, i removed the stock shaved head to put on a center firing head.

this is the only picture i have of the plug and that was about 15 minutes of 75-100% throttle. motor has since done about 1-1.5hrs on the new head and i will get a picture of the plugs today.

here also is a picture of the head with 1 odd hour on it (head is held upside down) the burn is all deposited on one side

**Fast Fred** · 05-27-2015

the plug looks a bit light, head looks ok, check thermo, make sure she gets to temp

**RWN50** · 05-27-2015

seal on the thermostat is average.

ill take a pic of plugs tonight and the head in a day or 2 when i take it off again to try another set of domes

**Revengable** · 05-28-2015

Originally Posted by RWN50

seal on the thermostat is average.

ill take a pic of plugs tonight and the head in a day or 2 when i take it off again to try another set of domes

Velocity stacks?
Electric fuel pump?
Is your cowling vented?

**champ20B** · 05-28-2015

Looking at that plug (mighty clean looking) and the patterns on the pistons (not the carbon patterns, but the clean metal patterns that line up with the ports) I would seriously check my oil reservoir, if so equipped. Condensation during hot and humid times of year will get water in these tanks over time. I saw a guy ruin a VRO Johnson because of this.