Carb mods for CMB .21 VAC?

Hi guys, I tried the new CMB .21 VAC engine this past weekend with no luck. We have for the last two seasons used the Zoom 21 carb for the Valvola and its an absolute dream to use. The stock CMB VAC carb seems to be not so Zoom like if I may say so...

I unscrewed the midrange needle so it was not in any way close to the spraybar but we could not get the geometry right. When looking at the holes in the spraybar (and blowing air through it) it feels like there would be enough flow but Im skeptical about that. If adjusted to about the same rich level we are used to with the Zoom it was to lean (eventually - when sticking the trigger WOT) on top end. If the third channel needle (Kalistratov/CMD) was adjusted so it was rich enough on WOT it was too rich to launch...

So what do you do for making it work?

I use 60% fuel and a Fat pipe.

Update: the spraybar hole is about 2.0 mm in diamter on the stock .21 VAC carb, possibly 2.1...

/Niklas

Hello Niklas, I know that it will not do you any good now, but the Zoom 21 carbs for the VAC engine will be avaliable this winter.

Charles

Charles Perdue said:

Hello Niklas, I know that it will not do you any good now, but the Zoom 21 carbs for the VAC engine will be avaliable this winter.

Charles

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Put me up for at least one... Need to find a solution to be able to at least test it before the water becomes hard again though. One solution would be to install an Valvola/Mac intake on it = Zoom.

Hello

Is there anyone known that have run an original CMB VAC21 engine in a rigger?

Jorgen

Jorgen Andersson said:

Hello

Is there anyone known that have run an original CMB VAC21 engine in a rigger?

Jorgen

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Hi Jorgen

Yes i know of one that is being curently run in the resaults so far are very good i will know more in a few weeks.

Paul

Hi Paul,

I would guess I will get some response from racers at the worlds in Hungary in about two weeks also but it sure is silent in here... h34r:

i hope to try mine out in a week or so. i will let you know after i get it going

chris

I have been testing and breaking mine in for a couple months now.

I have not had any problems with the stock carb.

I cut the low end needle off as i do not use it in my rigger.

I can slow down to almost a fast walk then open it up and away it goes.

I really like the motor alot and am swinging a ABC 1718 and 1816/3 cleaver with it.

Hopefully we will be going out again this weekend so i can do some pipe testing.

I also built a tank for the new boat and will also test that

as well.

Carl

Chris: yes, please let me know about the testing. From July 24 we're off to Hungary though for the NAVIGA worlds so my VAC testing will have to be after the worlds. Its not raceable for me at this point.

Carl: hmm. Ok, at least one that has it working out of the box.

Niklas:

what is your complete set up on the motor/pipe/prop/fuel?

Carl

carlnoki said:

Niklas:

what is your complete set up on the motor/pipe/prop/fuel?

Carl

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CMB ,21 VAC / stock timings / ODO blue plug / stock squish height as it was supposed to be the brake-in / CMD header / Fat pipe @ 200 mm / 60 % nitro / 14% Klotz super techniplate / Sholund H6-3.46 or 3.6 prop. But the carb "geometry" was so bad it wasnt even any idea to throw it in the lake sometimes... It actually just went good ONE tank. The rest of the times it stopped after a few feets. Im convinced if it had been a Zoom carb on it I would now tell everybopdy how good the VAC engine is. B)

set your head clearance to .006 inches (.1524 mm)

the blue plug is good for warm to hot weather.

if you have a purple one use that in a cool weather.

pull the pipe to 8 inches (203-205mm) to start with.

fuel is good choice.

if you have any OTHER ABC props, try the 1618 to start with then work towards the 1716, 1717, then 1718.

I use these series of props only now days. I have the older H series but they are in the prop box collecting

dust.

IF you have or know of anyone that has the BORIS flow meter, set the needle flow to 90 to start with

for an initial setting.

this will get it going pretty good, then you can start working on shortening up the pipe some and trying different props.

the pipe i am using right now is the andy brown STL bar stock pipe. (supposed to be similar to the fat pipe.)

I also do NOT use the low speed needle in my motor. (I cut it off)

and good luck in Hungary.

If you see Ian Folkson (FRS-V Great Brittain) tell him i said Hello.

Carl

carlnoki said:

set your head clearance to .006 inches (.1524 mm)

the blue plug is good for warm to hot weather.

if you have a purple one use that in a cool weather.

pull the pipe to 8 inches (203-205mm) to start with.

fuel is good choice.

if you have any OTHER ABC props, try the 1618 to start with then work towards the 1716, 1717, then 1718.

I use these series of props only now days. I have the older H series but they are in the prop box collecting

dust.

IF you have or know of anyone that has the BORIS flow meter, set the needle flow to 90 to start with

for an initial setting.

this will get it going pretty good, then you can start working on shortening up the pipe some and trying different props.

the pipe i am using right now is the andy brown STL bar stock pipe. (supposed to be similar to the fat pipe.)

I also do NOT use the low speed needle in my motor. (I cut it off)

and good luck in Hungary.

If you see Ian Folkson (FRS-V Great Britain) tell him i said Hello.

Carl

Click to expand...

Thanks Carl,

But the biggest issue was on the "pontoon", not in the water. So not so much fine tuning so to speak but more to get it going at all.

I did not cut the midrange needle off but it was unscrewed far-out. It felt like there was no good average needle settings at all. Too lean or too rich. But when it was "too rich" and I stuck the trigger WOT (not for too long of course) it eventually cleared out to almost go too lean on full blast on the pontoon. It was really strange and it just felt like there is a really bad balance between the carb air speed/venturi/spraybar size/suction.

Do note, the spraybar stock hole is a whopping 2+ mm in diameter!

I dont know Ian, but he will for sure be there I guess. I will say hi if/when I meet him. I race FSR-V3.5 also.

What are the main advantages with the 1618, 1716, 1717 & 1718 vs H6 & H7 in your mind? What cups etc have you used on a rigger on these? We look mainly for drive-ability and milling possibility - not WOT driving in "lane 4-5" for six laps. My other rigger takes most props but the nastier the prop the more peaky it will get of course and less nice to drive in heat racing. The S15 with 3.75 cup is no problem as an example but its not a race prop (on that boat) - at least over here. But it will for sure be an keyboard MPH bragging set-up, but as mentioned, thats not really what we do. Im open for most suggestions though!

/Niklas

niklas

i hope to have info on this in a week or so like we talked.. also try a 1445 octura cupped up or a 1450 cut down to 46-47 mm on that motor.

everything i have heard here in the states anyway alot of guys are running them STOCK with head clearance set around 6 - 8.

hope to have more info in a week or so

chris

Hello Guys

Paul - Nice to hear from, I hope that life is great for you.

Any plans for the Worlds in 2012?

Carl - Thanks for info, what rigger are you using the VAC in?

Please tell us more about your findings about the props you do mention.

Jorgen

Any ideas of how to make the VAC carburator work though?

Jorgen Andersson said:

Hello Guys

Paul - Nice to hear from, I hope that life is great for you.

Any plans for the Worlds in 2012?

Carl - Thanks for info, what rigger are you using the VAC in?

Please tell us more about your findings about the props you do mention.

Jorgen

Click to expand...

Hi Jorgen

WC 2012 thats hard to say its a long way off but you never know were is it being held?

Paul

Niklas, I'm not using pressure in FSRV as you know but using the midrange needle that has the round end as opposed to the one with the hex end the main needle has to be open a long way and midrange needle has to be in a long way, it stays inside the spraybar at all times. For me the MR needle with the hex end did not work so well, it is a thicker needle. Of course tolerances change and so not everything is the same on everyone's carb. . Overall I found this to be the best 21 carb that CMB has made although I have now changed the main needle to the OS radio type.

Dave

Hi Dave, thanks for some carb info! I unscrewed it from the get-go and felt the balance to be way off - actually not usable at all really (in hydro). Need to test it with the midrange needle screwed in but doubtful if time to do so before we leave for Hungary. With a 2+mm inside dia one for sure understands that the needle to stay inside the spraybar at all times anyways. Have yet to test it in my V boat though also. Maybe on Monday - in good time before the worlds... LOL

FYI: We where at the pond today for a shake down before the NAVIGA worlds in Hungary. There was another racer there with a stock VAC .21 (in a rigger) with the stock carb on it and his VAC did not work either. He actually had his mid range needle active and inside the spraybar (I had mine unscrewed) but there is just not enough torque/power to get it going. On a level of "bad" his was slightly less really bad but still totally undriveable...