Needle Valve Setting For CMB .67

[ReidCuddy]

I have a CMB .67 Greenhead in my 1/8th Scale U-3 Chrysler Jeep.

I have the stock remote needle valve opened one turn for the servo arm. Currently I am running 40% nitro, as I do not race. I was wondering how many turns to open the hex head of the needle valve. More details below.

I have been breaking the engine in and have run about 3/4 of a gallon through it. It is still running slow but continuing to get faster each day I run it. I have the hex head opened up about 5 or 6 turns. At one point, I was at 4 turns and it was running very slow. I kept opening it up until about 6 turns and it is now running faster than it ever has. However, it still is only running around half throttle. When I increase to 3/4 or full throttle, it slows down to what seems to be about 20% throttle, even though the carb is wide open. If I decrease throttle to about 30% and increase back to 50%, staying at 50% throttle, it runs its best.

When I start it on the stand, I have very good response from the engine, matching the carb opening closely. I can idle it, mid-range, and give it top-end briefly and it responds well. It doesn't seem to reach those rpms once in the water. I realize there is a load from the prop but the engine actually bogs down if I go above 50% throttle in the water, whereas on land it will increase accordingly. What should I do to get more rpms on the water? I am running an octura 3-bladed prop

Thanks for your help guys.

 

[Ray Sametz]

What's the plug look like after you go full throttle and it bogs down????

 

[ReidCuddy]

Never really looked at the plug after that happened. I'm new to the sport but I just looked at it now. The bottom of the plug threads is dark and oily and the coil is white.

 

[richard jones]

I have a CMB .67 Greenhead in my 1/8th Scale U-3 Chrysler Jeep.

I have the stock remote needle valve opened one turn for the servo arm. Currently I am running 40% nitro, as I do not race. I was wondering how many turns to open the hex head of the needle valve. More details below.

I have been breaking the engine in and have run about 3/4 of a gallon through it. It is still running slow but continuing to get faster each day I run it. I have the hex head opened up about 5 or 6 turns. At one point, I was at 4 turns and it was running very slow. I kept opening it up until about 6 turns and it is now running faster than it ever has. However, it still is only running around half throttle. When I increase to 3/4 or full throttle, it slows down to what seems to be about 20% throttle, even though the carb is wide open. If I decrease throttle to about 30% and increase back to 50%, staying at 50% throttle, it runs its best.

When I start it on the stand, I have very good response from the engine, matching the carb opening closely. I can idle it, mid-range, and give it top-end briefly and it responds well. It doesn't seem to reach those rpms once in the water. I realize there is a load from the prop but the engine actually bogs down if I go above 50% throttle in the water, whereas on land it will increase accordingly. What should I do to get more rpms on the water? I am running an octura 3-bladed prop

Thanks for your help guys.

Try opening the needle another turn, sounds like when it is at full throttle the air to fuel ratio is not correct and when U go to full throttle it is bogging,

dick

 

[Terry Keeley]

Lean!

Open the needle, on the bench there should be a noticeable "bog" when you open the throttle.