Plug fouling issue.

**Rower** · 07-09-2019, 12:42 AM

G’Day everyone.

My my first post here so apologies if this has been covered before or is in the wrong area.

I race a 2 stroke 25 hp Mercury ME 25 MH ( re badged Tohatsu). I have been using Maxima Castor 927 at 33:1 for the last 4 years with no issues. 2 years on current motor.
During the last two competitions, the motor has dropped down to one cylinder on start up. This clears up after 10 seconds or so. There is an oily residue on my plugs on inspecting them that has not been apparent previously. Normally plugs are dry and slightly brown.

I intend to to try going to a ratio of 50:1 and see if this makes a difference.
Willing to look at different oils.

Is there anything else I should be looking for as cause for this change?

**Merc 2.5** · 07-09-2019, 04:00 PM

I may b way off ,carb mota? but lots premixed 2 strokes seem do this after a decent idle, mainly after initial start up , not so bad after a gud run tho I would try lean out idle jets , depending on rpm u turnin ,a 50.1 mix could hurt it , have u did all the neccessary checks. Comp, fire ?

**Motv18** · 07-09-2019, 10:46 PM

Could have separated, a lot of stations here like to dump alcohol back in the tank after they pay to have no-alcohol delivered.

Possible weak spark, the oil has a higher aki and weak spark might just burn off the gas,

related to that would be compression,

on the odd chance you wer getting butyl ether oxidized fuel and they finally dropped it, you should read rich by up to 2-3 sizes.

As merc said try spark and compression first

**Rower** · 07-10-2019, 01:16 AM

Hi Merc/Motv18

Yes - carby motor. I’ve checked compressions and they have remained constant. Ignition seems to be ok on visual spark inspection but don’t have any means of testing actual output at the moment. Performance/top speed remains the same. Running between 5800 and 5900 dependant on the prop used/ tilt settings. Had previously been running 50:1 semi synthetic valvoline. Changed to the higher ratio castor 4 years ago and noteable improvement - no fouling plugs and cleaner carby.

Ill see see what I can find out about the fuel we are using. Jets are as standard - can’t change part numbers.

Motv18 - what is aki?

cheers guys.