Sport .20 setup issues

[Jarcaines]

I have a “Lee Craft” (Arno Britts) sport .20 with a CMB Beta EVO that I’ve been fighting for a while now. I’ve gotten the ride to settle down a little bit, but now I’m fighting my motor. I thought it was the needle, but I’m not so sure after a day of testing.

Currently it will run about 2 laps looking perfect and then fall off with out fail, every time after 2-3 laps. Any idea what could be causing that? Pipe is 7 1/4 from the back of the head. Motor has a KRE carb. Any ideas?

 

[Grimracer]

Likely the motor is taking on water...

Grim

 

[Jarcaines]

Good though Grim.

We were thinking maybe it’s getting to hot, since if dogs down after 2-3 laps and building some heat. Ran a round without the cowling and it stayed on for about 6 laps before I brought it in. Going to drill a few more holes in the cowl then play around a bit more with the pipe and needle. Unfortunately the next time I have to test will be at the Nats.

 

[Tommy Levescy]

Good though Grim.

We were thinking maybe it’s getting to hot, since if dogs down after 2-3 laps and building some heat. Ran a round without the cowling and it stayed on for about 6 laps before I brought it in. Going to drill a few more holes in the cowl then play around a bit more with the pipe and needle. Unfortunately the next time I have to test will be at the Nats.

Wrap your pipe and open the cowl up some more

 

[Jarcaines]

Yes, wrapping the pipe! Great idea.

 

[shoboat]

Jar,

You don’t have enough heat in the motor. Wrapping the pipe should
help and the Pipe works Very Well @ 8.5” center of plug to the weld
on the pipe. What prop, pipe, and fuel ️ % are you running?
A piece of foam up by the carburetor should stop any water from
bouncing into the carburetor. The CMB nitro pipe works very well
a touch longer than most think. With a little longer pipe length you
should have a more consistent heat racing set up for the LA Nats.

Just A Few Ideas,

Mark Sholund

 

[FloridaScaleBoater]

Likely the motor is taking on water...

Grim

Or the hull is taking on water

 

[Wasted wages]

Do you have a drain hole in the bottom of the motor compartment?
Cut up and put a piece of sponge under the motor near the carb ...

 

[Samuel Hagan JR]

Does it blow the plug when it dies? Have you tried changing fuel? We had a similar issue with ours and it was the fuel. Have you tried it with the stock carb back on it?

 

[ALLAN YUEN]

Any pictures? Will look around then find problem solve

 

[Jarcaines]

Does it blow the plug when it dies? Have you tried changing fuel? We had a similar issue with ours and it was the fuel. Have you tried it with the stock carb back on it?

It doesn’t die, it just falls off.

 

[Jarcaines]

Jar,

You don’t have enough heat in the motor. Wrapping the pipe should
help and the Pipe works Very Well @ 8.5” center of plug to the weld
on the pipe. What prop, pipe, and fuel % are you running?
A piece of foam up by the carburetor should stop any water from
bouncing into the carburetor. The CMB nitro pipe works very well
a touch longer than most think. With a little longer pipe length you
should have a more consistent heat racing set up for the LA Nats.

Just A Few Ideas,

Mark Sholund

Mark,
I am measuring my pipe length from the back of the head at the exhaust port (don’t like the extreme angle measuring from the plug) that’s where I got the 7 1/4. I’m using the CMB Nitro pipe and 60% nitro.

Unfortunately the boat is packed in the trailer now and I can’t double check the prop we settled on. I’ll keep all this ready when I get down to LA, thanks a ton for the help!

 

[Jarcaines]

Any pictures? Will look around then find problem solve

Unfortunately she’s all packed up for the Nats. I’ll get back to you in a week or so though. Unless it’s magically better!

 

[Wasted wages]

Fresh fuel ? High nitro fuel loves to suck moisture out of the air...

 

[Bradley Maglinger]

What is your deck clearance? Restricting water any?

 

[Grimracer]

also.. make sure the exhaust is out of the boat FULLY!

 

[Wesleys Custom Graphics]

I am having similar issues but I'm running the cmb carb with the idle needle cut off. Getting a new needle in a few days to see if that helps. Mine runs like a raped ape but wants to surge after a few laps and there is no midrange or idle.

 

[Grimracer]

Wes.. in my testing cutting LSN or backing them out has always proven to be a bad choice. It has been far better for me.. to TUNE that needle.

Keep us posted.

Grim

 

[Bradley Maglinger]

When I first got my CMB Beta motor in 2015 I would have this problem in my Redman Roundnose. What I found was that the motor was not getting enough heat, I wrapped the pipe, and restricted the water flow to the same flow number as my motor with a needle valve at the transom. I have since restricted my water even more which has allowed me to richen the motor more. My deck clearance is 8 thou, and I ran my CMB pipe at 8.5 with an M440, Low needle is cut out. I ultimately believe the betas like heat.

 

[Jarcaines]

When I first got my CMB Beta motor in 2015 I would have this problem in my Redman Roundnose. What I found was that the motor was not getting enough heat, I wrapped the pipe, and restricted the water flow to the same flow number as my motor with a needle valve at the transom. I have since restricted my water even more which has allowed me to richen the motor more. My deck clearance is 8 thou, and I ran my CMB pipe at 8.5 with an M440, Low needle is cut out. I ultimately believe the betas like heat.

Thanks Bradley, great info.

What do you mean by deck clearance?

Also, I measure my pipe from the exhaust port, not the glow plug.

The heat thing makes sense, but I was surprised that it ran so much better without the cowling. Any thoughts on why that would be?