New CMB 21 Rotor Assy

[BB Mods's]

Nope, it looks more like a 45/67/80/90 carb now, no offset bolts.

 

[Bill Gibson]

Nope, it looks more like a 45/67/80/90 carb now, no offset bolts.

But the whole unit will bolt directly to an 08/09 Valvola with no mods? Is that correct? I wonder how much it'll cost?.....

 

[dave roach]

Bill

Front housing,drum,carb some were around $200.00

Dave Roach

 

[Marty Davis]

I heard it said that it's because it's the first time we had a 21 where the conrod is not passing directly over the end of the induction tract. Who knows?

Dave

Dave,

Do you think this is the reason tho? Looking at a crank induction 21 the beam of the conrod partially obscures the induction tract for only the first part of the inlet duration, after that the big end of the rod is above the induction tract until the inlet duration is complete.

Ian

I don't know, its just an idea. Crankcase volume is not the reason, of that I'm sure.

Dave:

Are you running the Carb as it comes or are you doing anything different? I had a little trouble with the low speed needle setting, but I had another problem which might have contributed to the setting problem.

Marty, I'm running the stock carb bored out a little. I had no problem with the carb or low speed needle. I'm just converting mine to use the OS radio needle.

If the boat is not on the stand perfectly level the motor floods very easily because the carb is so low compared to the fuel tank.

Dave

Dave:

Are you still running the low speed needle assy? You say you are converting to OS. Do you mean that you are using an OS Mixture control? If so are you using a seperate block or adapting to the carb?

How large can you bore the carb and still draw well?

Thanks for your input....

 

[Marty Davis]

Bill

Front housing,drum,carb some were around $200.00

Dave Roach

A little less I think....

 

[Stuart Barr]

The 21 VAC induction (Drum Housing, Drum and Carb) requires a slight beveling on the case to make the O ring seal on the older motors. Otherwise, it bolts directly on Valvola style motors. We have found that the set screw that holds the drum ramp needs to be loctited in place. Some of these screws have backed out and cut into the housing bushing. Price for all three parts to upgrade your motor is $200. These parts and the new 21 VAC's have not been shipped yet. Hopefully, I'll receive these in around three weeks.

 

[DaveMarles]

[quote

Dave,

Do you think this is the reason tho? Looking at a crank induction 21 the beam of the conrod partially obscures the induction tract for only the first part of the inlet duration, after that the big end of the rod is above the induction tract until the inlet duration is complete.

Ian

I don't know, its just an idea. Crankcase volume is not the reason, of that I'm sure.

Dave:

Are you running the Carb as it comes or are you doing anything different? I had a little trouble with the low speed needle setting, but I had another problem which might have contributed to the setting problem.

Marty, I'm running the stock carb bored out a little. I had no problem with the carb or low speed needle. I'm just converting mine to use the OS radio needle.

If the boat is not on the stand perfectly level the motor floods very easily because the carb is so low compared to the fuel tank.

Dave

Dave:

Are you still running the low speed needle assy? You say you are converting to OS. Do you mean that you are using an OS Mixture control? If so are you using a seperate block or adapting to the carb?

How large can you bore the carb and still draw well?

Thanks for your input....

I am still using the low speed needle and metering seems to be perfect and non critical. I bored the carb to 9.5mm and it seems to have no problem. I also took another carb out to 10mm . It didn't close fully but still throttled well although I'm not racing with that carb yet. I've adapted the OS radio needle to the original CMB spraybar. I was going to make a new spraybar to fit the OS RNVA but got lazy and machined the parts down and silver soldered the brass OS part to the CMB spraybar. Thats the radio needle part# 71703009.

Dave

 

[K-ZAM]

Just curious, whats the price of the 21 VAC engine?

Thanks

 

[dave roach]

Kentley

I hope you are sitting down.

 

[Marty Davis]

[quote

Dave,

Do you think this is the reason tho? Looking at a crank induction 21 the beam of the conrod partially obscures the induction tract for only the first part of the inlet duration, after that the big end of the rod is above the induction tract until the inlet duration is complete.

Ian

I don't know, its just an idea. Crankcase volume is not the reason, of that I'm sure.

Dave:

Are you running the Carb as it comes or are you doing anything different? I had a little trouble with the low speed needle setting, but I had another problem which might have contributed to the setting problem.

Marty, I'm running the stock carb bored out a little. I had no problem with the carb or low speed needle. I'm just converting mine to use the OS radio needle.

If the boat is not on the stand perfectly level the motor floods very easily because the carb is so low compared to the fuel tank.

Dave

Dave:

Are you still running the low speed needle assy? You say you are converting to OS. Do you mean that you are using an OS Mixture control? If so are you using a seperate block or adapting to the carb?

How large can you bore the carb and still draw well?

Thanks for your input....

I am still using the low speed needle and metering seems to be perfect and non critical. I bored the carb to 9.5mm and it seems to have no problem. I also took another carb out to 10mm . It didn't close fully but still throttled well although I'm not racing with that carb yet. I've adapted the OS radio needle to the original CMB spraybar. I was going to make a new spraybar to fit the OS RNVA but got lazy and machined the parts down and silver soldered the brass OS part to the CMB spraybar. Thats the radio needle part# 71703009.

Dave

Dave:

Did you see a visual performance increase with the enlarged carb? Are you using this on the enduro boat or hydro? Is there a great difference in the requirements of your enduro boat vs hydro? If I remember, you were running a geared setup on the enduro boat and needed super rpm's. Fill me in on the difference in our applications if you can.

 

[DaveMarles]

[

Dave:

Are you still running the low speed needle assy? You say you are converting to OS. Do you mean that you are using an OS Mixture control? If so are you using a seperate block or adapting to the carb?

How large can you bore the carb and still draw well?

Thanks for your input....

I am still using the low speed needle and metering seems to be perfect and non critical. I bored the carb to 9.5mm and it seems to have no problem. I also took another carb out to 10mm . It didn't close fully but still throttled well although I'm not racing with that carb yet. I've adapted the OS radio needle to the original CMB spraybar. I was going to make a new spraybar to fit the OS RNVA but got lazy and machined the parts down and silver soldered the brass OS part to the CMB spraybar. Thats the radio needle part# 71703009.

Dave

Dave:

Did you see a visual performance increase with the enlarged carb? Are you using this on the enduro boat or hydro? Is there a great difference in the requirements of your enduro boat vs hydro? If I remember, you were running a geared setup on the enduro boat and needed super rpm's. Fill me in on the difference in our applications if you can.

I am running FSRV enduro boats where throttling is of utmost importance. It's faster with the bigger carb. CMB told me the engine did not like a big carb but thats not my experience.

 

[BB Mods's]

Little OT, but can you explain your FSR-V fuel systems a bit? im interested in the float tank mainly.

also, whats the top speed you guys are seeing on the .21 FSR-V boats?

 

[Stuart Barr]

Just curious, whats the price of the 21 VAC engine?

Thanks

As Dave said, hope you are sitting down. $475.00. Once you see this new motor run you'll see it is worth it. One of these days Mark Grim will post his findings with this motor.

Stu

 

[tnrcboatracer]

I heard it said that it's because it's the first time we had a 21 where the conrod is not passing directly over the end of the induction tract. Who knows?

Dave

Dave,

Do you think this is the reason tho? Looking at a crank induction 21 the beam of the conrod partially obscures the induction tract for only the first part of the inlet duration, after that the big end of the rod is above the induction tract until the inlet duration is complete.

Ian

It is similar for the intake tract direction; the intake port in the drum is closed for most of the time the transfer and boost ports are open. Of course there is the inertia for the flow that may keep it moving in the direction of the sleeve ports.

The case volume difference I was referring to is the inside of the drum. Are you saying that the 'core of the drum up to the projected OD of the port is only 0.3cc? I think that it is more on my MAC21, but I have not measured it. THe machining in the housing of the VAC needs to be considered as well. With that considered the difference might be only 0.3cc. I think the more direct flow direction would definitely help the torque on the bottom end as it will increase the port velocity and scavenging. I wonder about the top end.

 

[DaveMarles]

I heard it said that it's because it's the first time we had a 21 where the conrod is not passing directly over the end of the induction tract. Who knows?

Dave

Dave,

Do you think this is the reason tho? Looking at a crank induction 21 the beam of the conrod partially obscures the induction tract for only the first part of the inlet duration, after that the big end of the rod is above the induction tract until the inlet duration is complete.

Ian

It is similar for the intake tract direction; the intake port in the drum is closed for most of the time the transfer and boost ports are open. Of course there is the inertia for the flow that may keep it moving in the direction of the sleeve ports.

The case volume difference I was referring to is the inside of the drum. Are you saying that the 'core of the drum up to the projected OD of the port is only 0.3cc?

The total crankcase volume which includes the inside of the drum on the RS07 is approx 0.3cc more than the new motor. The volume inside the RS07 drum is much more than 0.3cc but there is additional volume in the EVO with the machined ramp inside the crankcase above the drum housing and the actual volume of the top of the inlet tract in the EVO drum housing.

Dave

 

[DaveMarles]

Little OT, but can you explain your FSR-V fuel systems a bit? im interested in the float tank mainly.

also, whats the top speed you guys are seeing on the .21 FSR-V boats?

There is a good video here


These boats are running 75 to 85 kph.

I can explain by email the fuel systems . [email protected]

Dave

 

[Buckshot]

I am running FSRV enduro boats where throttling is of utmost importance. It's faster with the bigger carb. CMB told me the engine did not like a big carb but thats not my experience.

Little OT, but can you explain your FSR-V fuel systems a bit? im interested in the float tank mainly.

also, whats the top speed you guys are seeing on the .21 FSR-V boats?

There is a good video here

Now I understand why you guys in FSRV enduro need to have good throttling.....................So you can miss the retrieve boat!!!!!!!!!!!!!!!

:blink: :blink: :blink:

 

[BB Mods's]

Let me be the first to say that was insane! I had NO idea the 90 boats moved that fast!

Kinda makes me want one now

 

[D-7]

Hi All,

contact James Clegg, he visit sometimes FSR-V races in germany, it´s complete different to mono/rigger racing.

The qualifications going 20 minutes and the final 30 minutes - nonstop !!

 

[Joe Wiebelhaus]

That was crazy, I saw a guy go after his scale boat once during a heat, we freaked !!!!