OS-50 running cold at less than 1 turn!!

[comeflywithme]

Hi,

I was wondering if anyone could help me with this problem.

I have recently changed back from using 30% nitro to 20% and have had some problems ever since. I'm running a zimmerman pipe and about 1900rpm HS.

As normal I simply set up the engine until the backplate is around 60deg C (can be touched for up to 5secs). Following this I was however shocked to find that I was running at a needle setting of only 3/4 of a turn out from closed!. I also found that the engine would die occasionally if I do fast climbouts and bog very badly on continuous flips and tic tocs. - I got to do lots of autos over the past month!!

Richening the engine to around 1 and a quater will give loads of smoke, reduces bogging and elliminates flameouts. However the down side is that the engine is barely 40deg C on the back plate at that temp. I have also started using a carb smart unit and even when set to 90deg C (head) it will try to go back to less than 1 turn on the mixture needle which brings with it risk of the flame outs described above.

Could it be that my low mixture setting is wrong? I have noticed that the engine screams its n%£s off when I start the engine, oscillating in rpm and only settles into a decent idle speed after I've taken off or run the engine up.

I have taken the engine appart and found no unusual signs of wear and have changed glow pugs which has made no difference

Looking forward to any help I can get on this

Thanks

[DavidH]

Nitro content does really not have much affect on needle settings. But difference in oil content and type of oil can make a big difference in needle settings. Even when using the same nitro content.
For example, I have used 30% nitro and 22% low viscosity oil fuel. I then used the same fuel 30% nitro and 14% low viscosity oil. I had to lean the main needle nearly a half turn to get the motor to run the same on the lesser precentage of oil compared to the more precentage. The only difference between the two fuels was the precentage of oil. With the more oil content the needle needed to be more open ( richer) than it did with the lesser oil content.

David