CMB .67 Purple Head Info

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Daniel Woody

Member
Joined
Nov 19, 2022
Messages
7
Attempted building a 1/8 scale hydroplane in the early 2000’s and unfortunately due to finances had to sell before finishing the boat. Saw this for a good price the other day and decided why not. There isn’t much info online about this CMB 67. Who can share what they know? Year, model, output power. Recommended tips to tune or make more power. Are there spare parts available? How does it compare to the green gold or blue heads? How many ports. Are parts available to do a remote needle? Any helpful info or documentation.
 

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RaceMechaniX

Well-Known Member
Joined
Apr 27, 2007
Messages
3,021
Daniel,

It's recommended to pull the motor all the way apart and clean it thoroughly. If this was a new motor check for any residual machining chips or loose debris. Often the chrome plating leaves a sharp brittle edge on the liner ports. Use a small carbide burr to remove these and some cratex bits to knock off any other sharp edges. Thoroughly wash with brake cleaner or white gas.

Set the deck height to .010-.012". Depending on the % nitro you run you may want a different volume head button. It's like a 3+1 port configuration. You will want a remote needle valve to control the mixture. There are many options to choose from: stock CMB needle, OS inflight with appropriate base, Fuel Doctor, BVM jets needle or speedmaster. For a scale set the pipe length between 11.5-12". The timing from factory is likely OK for a scale.
 

Daniel Woody

Member
Joined
Nov 19, 2022
Messages
7
Daniel,

It's recommended to pull the motor all the way apart and clean it thoroughly. If this was a new motor check for any residual machining chips or loose debris. Often the chrome plating leaves a sharp brittle edge on the liner ports. Use a small carbide burr to remove these and some cratex bits to knock off any other sharp edges. Thoroughly wash with brake cleaner or white gas.

Set the deck height to .010-.012". Depending on the % nitro you run you may want a different volume head button. It's like a 3+1 port configuration. You will want a remote needle valve to control the mixture. There are many options to choose from: stock CMB needle, OS inflight with appropriate base, Fuel Doctor, BVM jets needle or speedmaster. For a scale set the pipe length between 11.5-12". The timing from factory is likely OK for a scale.
Thanks for the info. Do you know what years this was manufactured and how it compares to other CMB 67 models?
 

RaceMechaniX

Well-Known Member
Joined
Apr 27, 2007
Messages
3,021
I am guessing pre 2000. It's probably not on par with the latest generation, but should not be too far off.
 

Tommy Levescy

Well-Known Member
Joined
Mar 29, 2014
Messages
409
I am guessing pre 2000. It's probably not on par with the latest generation, but should not be too far off.
we have the same engine in our Winston Eagle Lobster and it runs like a bat out of hell. Probably one of the fastest scales in Norcal. Change the carb to a Os9b and do not modify it. Just set the clearance like tyler said to do. Break it in and she'll run great. We missed the national record with ours by a few tenths earlier this year before the records all fell off. We run ours on 60% with a non drilled out Andy Brown Parabolic .67 pipe. It pulls a x457/3 blade all day long(it actually has the prop Don Ferette set the record with on it from what the original builder told us).
 
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