Need advice for fuel mixture richness

[Julien4788]

Hi,

 

I am wondering if someone is used to dealing with carbs here. I have replaced my ros 125 head so now it runs richer but looks too rich to me. any second thoughts would be appreciated. It has a wg8 carb the spark plug pic is after a 1h30 flight

 

[Julien4788]

i didn't really idle the engine much before landing maybe 20 seconds max . It seened to run fine but i want to make sure it's okay to run it like that or if it could cause damage.

 

Since it doesn't have top end adjustement i am unsure how to go about it

 

Edited December 12, 2020 by Julien4788

[admin (Simon W)]

@Pete S is the man for that

SW

 

[Julien4788]

I will also note it was -1 celcius and that mi fuel mixture is 2.5%

[Julien4788]

[Pete S]

Going on the colour of the plug electode, the mixture is spot on. You do seem to have a small build up of carbon around the bottom of the plug, what oil are you using?

[Julien4788]

1 hour ago, Pete S said:

Going on the colour of the plug electode, the mixture is spot on. You do seem to have a small build up of carbon around the bottom of the plug, what oil are you using?

Hi! thanks for your input i appreciate it. I am using Redline two stroke racing oil. I only have 500ml left. I will use motul 710 after that.

[Pete S]

I suspect that the cold temperature is keeping the head cooler than normal hence the oily deposits on the bottom of the plug.  You mentioned that you had replaced the head, what was the reason?  If the engine is starting easily and accelerating to full power without hesitating when warmed up, the low jet is almost certainly set correctly, and as you say the high jet is fixed so carb would seem to be ok. With a few exceptions fuel/carb problems (filter dirty, diaphrams worn out, primer valves failing) usually cause a weak mixture which can cause engine damage. A rich mixture won't damage the engine but can cause issues over time (carbon build-up fouling the plug and excessive deposits on the piston and head). 

It will be interesting to see if changing the oil reduces the oily deposits, after cleaning or replacing the plug.

As an aside, to get the most accurate plug colour indication the engine should be at normal running temperature, run at full power for a minute or two and killed from full power.

[Julien4788]

one of the previous owner had cracked the head probably from  putting bad or low octane gas i was told. So it was spewing out gas but didn't leave any deposits the color of the plug was perfect (like the electrode now but all of the spark plug but i didn't run the engine during summer yet)  It has lots of compression now and at -1c it started  after around 5 pulls. I wouldn't be surprised if the new oil causes less deposit since the burning temperature of motul 710 is 30°c lower. For now it will probably be even richer we got real winter temps coming our way (-10c this week and after Christmas it's supposed to go down to -20/-25 )