Sport .20 setup issues

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Jarcaines

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Jul 14, 2008
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254
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?
 

Jarcaines

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Jul 14, 2008
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254
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

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Mar 29, 2014
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341
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
 

shoboat

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Joined
Jun 23, 2002
Messages
7,109
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
 

Samuel Hagan JR

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Jul 18, 2010
Messages
4,182
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?
 

Jarcaines

Well-Known Member
Joined
Jul 14, 2008
Messages
254
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!
 

Wesleys Custom Graphics

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Joined
Nov 18, 2005
Messages
1,493
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

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Joined
Dec 27, 2001
Messages
8,302
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

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Joined
Sep 23, 2012
Messages
1,424
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

Well-Known Member
Joined
Jul 14, 2008
Messages
254
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?
 

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