Piston burn pattern?

[RWN50]

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

http://i59.tinypic.com/2d9zled.jpg

[Fast Fred]

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

[RWN50]

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]

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

[champ20B]

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

[RWN50]

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

http://i62.tinypic.com/2z7qxwx.jpg
http://i58.tinypic.com/16m982.jpg

[Fast Fred]

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

[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

[Revengable]

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]

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.

[RWN50]

Revengable - No stacks but have installed them in the last day, mechanical pump and the cowl isnt vented more than stock

Champ20B - Its premix and i often run a cap of metho every few tanks to dissolve the water. We do have a problem with water ingress slightly as we use it alot in the surf.

Here is the plug that came out of the stock head when the picture was taken, done about 15 hours. i did cut one open and it had a carbon ring very black at the bottom and about 0.8mm wide
http://i61.tinypic.com/rv9fli.jpg
http://i57.tinypic.com/200wbi0.jpg
http://i61.tinypic.com/i4pfm8.jpg

Here is a pic of the plug that came from the center firing head, about 1.5hrs on it, looks a bit wet though as i washed the motor out after last run (in the salt) so its very wet from idling
http://i59.tinypic.com/aauqsi.jpg
http://i58.tinypic.com/2pqulid.jpg

[Revengable]

This one will suck water if all the pan openings are not sealed.....you can feel it in the buttdyno....your pistons look like they've been steam cleaned.59716:

[Revengable]

59717
This one will suck water if all the pan openings are not sealed.....you can feel it in the buttdyno....your pistons look like they've been steam cleaned.59716:

[Powerabout]

maybe a combustion chamber moved over toward the inlet side?

[ice_spy]

I'm no expert but here's my suggestions.
30 psi extra compression, +98oct might be causing pre ignition. Have you changed the timing? Maybe 91 ron would be better, can you hear pinging up top, maybe the crank has twisted and timing is slightly out?

I would be running a little more oil than 50:1 if you are revving beyond factory limit.

Possible water leak into pistons from blown head gasket? maybe caused from a higher compression.
Is the little amount of added metho causing a hotter burn? Maybe best to run a water fuel separator if space available.

[Powerabout]

How can 91 prevent pre ignition if 98 cant?

[Krazy Karl]

I am not going to reveal my methods for fear of starting unruly discussion but a long time boat racer showed me how a spark plug reading can reveal timing settings. The timing on these last plugs show a variance from cylinder to cylinder and overall the timing is out of wack. I am not going to say my method is fool proof but it was pretty much in the ball park on my Yamato. I agree that there is something definitely wrong on the first set of plugs. It looks like water intrusion to me too. I am not too familiar with Tohatsu's, whether timing can be set for each individual cylinder or not. If not I would be real concerned with the crank being twisted which can happen on a Tohatsu. Has it been welded or not? I don't want to scare you but there are some issues that need to be investigated.
kk

[Revengable]

This little jewel was a dog when we got it. Three threads too much timing. After timing per Sid Bass it came alive. This semi-hemi head was made by Outboarder. 70 hp carbs on M50D2 59718

[ice_spy]

That's a mean looking tohatsu !
Powerboat, sorry I meant 91 lower octane might be better suited.
I think it looks more like water but. What's the silicon(?) around the head ? Was it used with an old head gasket?

[RWN50]

Didnt get a chance to pull the head off this weekend but will hopefully do it before the end of the week and post photos.

As far as timing goes its slightly less than factory 20 degree.

motor did 130 hours with stock limiter on and was stock, i then rebuilt it and did some work and welded the crank. there is no vibrating comeing though the motor being out of balance of firing wrong.

Revengable, what rpm are you pulling from those motors, what jets and mixture are you running and what do you set your timing advance to?

[Krazy Karl]

I don't know Tohatsu's but 20 degrees? I know modern engines don't need as much lead as older ones but that sounds awful low. Merc 55H's run 40 per the factory but will take more depending on setup.
kk

[Revengable]

The Dmod(stock) is jetted one step leaner than stock in #1 ,#2.... #3 is the same jet size but that's 2 steps leaner than stock... 6500 rpm calculated....100 octane mixed 24:1 with real dino oil... if you time them up they won't pull.

[Roflhat]

I'm going to try more oil in mine, the CES runs best at 32:1 apparently.

[Fast Fred]

loopers, the higher in rpm you spin them the less timing it will tolerate. smoked set after set of pistons on the ces tryin to get her to pull hard on the low end. that high rpms timin needs to be low or she just burns the piston at the exhaust port window. the more timin it has the harder she pulls on the low end but she fights it's self at high end.

[Fast Fred]

cross flows, use about twice the timin