CMB 45HR in a Sport 40

[Mike Betke]

I have run this engine in my sport 40 for 2 years and have no problems. Boat is to fast and will not stay on the water. Here's the trick.

Head volume has to be .44cc set at .010 head clearance. Parabolic pipe at 9.5 inches. OS 40A carb. Everything else is stock inside the motor. The stock carb is really big, but it should at least get up and run.

I have run other pipes with even better results, but I like the parabolic for racing. The trick is the head volume. I ran the stock head and had a lot of detonation in both a rigger and sport 40. Since I opened the head up, it still looks like the day I pulled it off the lathe and I have been running the same plug all year long. Now I have to design a boat to stay on the water better.

 

[Bert Dygert]

Mike,

Mike B. has the points lead for sport 40 in district 2. His set-up should sound familiar. The only difference is the pipe. I'm running a CMB nitro pipe with a muffler. I may have to try a different pipe now.

Bert Dygert

 

[BobGutsell]

One more thing, I forgot that I had the bore of the the carb sleeved down as well I think it's now 10 mm diameter. The carb that came with the engine was bigger than what comes on a 67 engine!

I usually run a CMB EVO Silenced pipe, but have an AB45 pipe to run that I haven't used yet.

Mike Betke, do you run the stock CMB header cut down, or do you have an alternative that will slide inside the AB pipe, the one I have is smaller ID than the CMB pipe?

 

[Mike Starrett]

I have run this engine in my sport 40 for 2 years and have no problems. Boat is to fast and will not stay on the water. Here's the trick.

Head volume has to be .44cc set at .010 head clearance. Parabolic pipe at 9.5 inches. OS 40A carb. Everything else is stock inside the motor. The stock carb is really big, but it should at least get up and run.

I have run other pipes with even better results, but I like the parabolic for racing. The trick is the head volume. I ran the stock head and had a lot of detonation in both a rigger and sport 40. Since I opened the head up, it still looks like the day I pulled it off the lathe and I have been running the same plug all year long. Now I have to design a boat to stay on the water better.

Sounds like you got HR's all figured out. Thanks for the great info! Now to see if I can find a 40A carb. Tower's out till September. Thanks, Mike

 

[Lay26]

one of the best pipes i ran with this motor was the ops 60 pipe with a reduced stinger diameter.i found this motor the carb was too big and had another carb made for it that brought the boat alive....i also used a smaller prop 450/2 reduced

 

[Mike Betke]

One more thing, I forgot that I had the bore of the the carb sleeved down as well I think it's now 10 mm diameter. The carb that came with the engine was bigger than what comes on a 67 engine!

I usually run a CMB EVO Silenced pipe, but have an AB45 pipe to run that I haven't used yet.

Mike Betke, do you run the stock CMB header cut down, or do you have an alternative that will slide inside the AB pipe, the one I have is smaller ID than the CMB pipe?

I run the stock header with the pipe butted up to it. They are about the same size on the one that I have. When I get time I was going to weld a piece to the pipe so it slides over the header so it doesn't beat it up so much.

 

[Mike Betke]

I have run this engine in my sport 40 for 2 years and have no problems. Boat is to fast and will not stay on the water. Here's the trick.

Head volume has to be .44cc set at .010 head clearance. Parabolic pipe at 9.5 inches. OS 40A carb. Everything else is stock inside the motor. The stock carb is really big, but it should at least get up and run.

I have run other pipes with even better results, but I like the parabolic for racing. The trick is the head volume. I ran the stock head and had a lot of detonation in both a rigger and sport 40. Since I opened the head up, it still looks like the day I pulled it off the lathe and I have been running the same plug all year long. Now I have to design a boat to stay on the water better.

Sounds like you got HR's all figured out. Thanks for the great info! Now to see if I can find a 40A carb. Tower's out till September. Thanks, Mike

Mike,

I forgot about the sleeve I made to insert into the housing so that the throat is the same diameter as the carb. The stock carb has a neck that inserts into the housing, but the OS is a flush mount. I would suggest doing this to reduce the volume in the housing. Modify the head and try the stock carb. It should get you going. The OPS pipe will work good to. The main reason I use the parabolic is that it fits in the boat better. I would run the other pipes a little longer to start as I have always been able to run the parabolic on the short side compared to other pipes.

 

[Mike Starrett]

Right now I have an RS carb on it. It is smaller inside than the HR carb. I had a nylon sleeve made the same ID as the carb to go in the housing. I think I may have an OPS 67 silenced pipe here to try also. I'll try some of these things this Sunday. I really appreciate everyone's advice. Mike

 

[Lay26]

its the ops 60 nitro pipe that worked really well ....the one that you need an add on muffler

 

[Dasboatman]

Hey Mike Starrett,

Meant to ask what hull that is you have in my initial post. Brain Fade took over and I forgot .

Mike Betke and Leighton,

I believe that OPS 60 Nitro pipe is Art. 6280 - has a 5 3/4" perimeter at the high point of the cone.

What ID have you reduced the stinger to? I believe stock was .470, I have been trying in the .345 ID range.

I want to try an internal stinger with them next to see what the noise reduction actually is compared to stock, and with Rum Racing tip muffler.

CHEERS !!! Bob

 

[Mike Starrett]

The hull is just one I designed and built. I had a Whiplash before and it was good but there were just some things I didn't like about it. I mainly wanted a deeper hull to hold fuel tanks under the deck and a bigger radio box. I just designed it and built it to suit my personal construction technique. I have no interest in glass work so I used a Dumas 40 ABS tunnel cowl. As compared to other boats it has some rather odd dimensions and shapes. Mostly due to just building and fitting as I went. I've had it in the water a few times and I like the way it drives.

 

[Dasboatman]

Hey Mike,

Roger that. Nice to see something different every once in a while - Nice job!!!

I modeled with balsa wood until I started building boats in 1970. Having worked with birch ply since, I no longer have the finesse required for the lighter material. A sanding block with 60 grit sand paper doesn't work well with balsawood - Har Har!!!

CHEERS, BOB

 

[Bert Dygert]

Mike,

We're you able to do any test last weekend? Any signs of improvement?

Bert Dygert

 

[Mike Starrett]

Mike,

We're you able to do any test last weekend? Any signs of improvement?

Bert Dygert

No , I went but ended up spending most of the day working on other peoples stuff. By the time we got that working I was too hot and tired to try it. I hope to get to try it this Saturday.

I'll post here how it goes. Thanks, Mike

 

[SeanKewley]

I run a CMB 45HR in my SS45 with good results. It likes a small prop and high rpms. I use a MACs 10cc tune aero pipe set at 10.5" with a m447 or a detongued x448.

 

[Bert Dygert]

Sean,

Do you measure the Aero pipe to the first weld seam? Or to the middle of the straight section?

I want to try one on my HR motor. New tank just arrived from Walt today.

Bert Dygert

 

[SeanKewley]

I measure to the rear converge (the point where the flat starts to neck down). The sweet spot seems to be between 10 15/16" and 10.5" on that pipe with the smaller diameter props.

 

[Eric Canto]

Mike,

I had an HR in my sport 40 from Teddy. He got so frustrated with it he sold it. I also got frustrated with it and sold the motor to Eric Canto, who was also going to put it in a sport 40. The engine seemed like it would be great in a rigger, but it just didn't like the 10 lb boat it was in.

It looks like you've done everything right so far! I put a hopper tank next to the needle like you have and it helped a lot but still wasn't reliable. There may be something to that fuel draw issue someone mentioned. I never tried a smaller carb, do you have one that will fit?

That motor went into an AC sport 40 and has been running fantastic from day one. My friend that owns the boat is out of town for an extended period but when he returns I will get him to post a video of the boat.

 

[Jeff Schindler]

Mike,

I had an HR in my sport 40 from Teddy. He got so frustrated with it he sold it. I also got frustrated with it and sold the motor to Eric Canto, who was also going to put it in a sport 40. The engine seemed like it would be great in a rigger, but it just didn't like the 10 lb boat it was in.

It looks like you've done everything right so far! I put a hopper tank next to the needle like you have and it helped a lot but still wasn't reliable. There may be something to that fuel draw issue someone mentioned. I never tried a smaller carb, do you have one that will fit?

That motor went into an AC sport 40 and has been running fantastic from day one. My friend that owns the boat is out of town for an extended period but when he returns I will get him to post a video of the boat.

That's awesome news Eric!