2 barrel carb

[El Zorro]

Back in the late 1980's ( 1980's technology, anyone? ) I played around with a .21 Mono and pressurizing the fuel tank with crankcase pressure from the engine. From what I can remember now, crankcase pressure is somewhere around 2 or 3 times more than typical pressure from a tuned pipe. Only drawback to using crankcase pressure was that you had to incorporate an on-off valve between the remote needle valve and the carburetor. This valve was operated with the throttle servo. When the engine was operating at full throttle the valve was shut, allowing pressure to build up in the tank. When you started closing the throttle, the valve would open which would allow pressure to bleed off from the tank. If all of this extra pressure stayed in the tank when you throttled back the engine would flood and cut off. Initial runs showed that the system did indeed work, but I didn't really see enough gains in performance to warrent the extra work in putting this in the boat. Just something else to go wrong, you know? Another idea from my controline flying days..............

Dick Tyndall

In the early 70's, Leland Morton and I had a 2 stage fuel valve in a B Proto ship that was centrifugaly operated. It had a primary jet for takeoff and a secondary that opened when the centrifugal force overcame the spring.(When it came on the pipe after takeoff). We flew that setup sucessfully for about a year and half. It worked well at times, but didn't have consistancy. The KISS principal is the winner in most cases. In my experience, you also can't give up the velocity in the venturi, or make the case so large that it suffers for lack of base compression. Bigger is not always better. It still has to pump.

Actually, the on-off valve was MOUNTED between the remote NV and the carb. The only fuel tubing connected to the valve went directly to a third line into the fuel tank. The controline people that flew the Navy Carrier event used this type of fuel system to fly fast laps and some very SLOW laps, also.

Bob keeps bringing up names from the past that sound familar. I believe that the FAI Speed fliers used something similar.............weren't they called "speed switches" or something like that?

Dick

 

[DougSchultz]

I have seen something similar done on a 40 outboard. Manifold built to accept two carbs. This engine also had two tuned pipes! It ran but was not very fast. The old Johnson Stinger 3 cylinder outboard could be modified to accept 3 two barrel carbs instead of 3 one barrels. But part of that mod was seriously enlarging the intake tract to make good use of all that extra fuel and air. Making more fuel and air "available" does not always mean more power on a two stroke engine. Crankcase volume, cylinder volume and RPM limitations will dictate how much the engine can suck in and blow out. Your linkage idea is interesting.

I have messed around with those OMC 3 cylinder 49.7 cu. in. outboards quite a bit. We have tried the larger two barrel carbs. And like Mark says there is a lot more factors to modifying the engine horsepower than just fuel. If you are pumping in more fuel you also need to get more exaust out. The engine we run at this time on a GPS runs right at 97 MPH (testing, not race conditions) We are running the 1 1/16 bore carbs with the idle jets removed and the intermediate and main jets opened up just a couple sizes. On a flow bench we have found that these carbs with the factory air silencer has better fuel air ratio than any thing else we've tried.We have a 3 pipe megaphone exaust.

 

[Mike Larson]

Doug... Marty is lookin to get to your shop soon, Kneel down ideas... Id also like a look at the adjustable fixtures on your pipes, Nightmare got the wheels grindin......

 

[Nigtmare]

Dick,

You make yourself sound old! Just the fact that I got some of you old farts right up in here has put a smile on my face. bigger is not always better but I think that nitro engines have a lot of potential, and they can push their limits with some different combinations. It's funny how an electric boat can do 140 mph with the same props we use and, basically, the same type of the boat. I know the rpm and the torque is above the nitro engine, but only because of what we use. The problem we're having with our engines is that we need the torque on the bottom end to launch the boat, and that compromises the top end. Then, we compromise the bottom end by using smaller props, and take the torque away from our engines. I have a screaming engine with not enough prop. A two-stage carb or a two barrell whatever will give us the bottom end to launch the boat with a big prop, and have the rmps on the top end. I'm not saying that this is an easy thing to do...it will take a lot of trips up to the pond, but it can be done. If carboration is not the answer, then what is? We have maxed the engines with modifications, and we don't see any increase in mph. With a two stroke engine, part of the carboration is the pipe, and those two have to be worked out at the same time. This two barrell carb I'm thinking of can have a single barrell with two different size holes drilled in them, and a different positioning of the hole. So, there's no linkage involved between the two barrells. A standard needle will regulate the primary and a remote needle will regulate the secondary. A buddy in our club meeting today gave me someone's name that might want to tackle this. If anyone has any ideas of how to make this thing, or can design one on the computer in some of your spare time please let me know. This is not a business venture, it's just an idea to get our hobby forward or ten yards behind! :lol:

Thanks,

Nick

 

[El Zorro]

Hey Nick,

Most of us "old farts" like to hear about others doing a little thinking "outside of the box" ( like Don always says ). Have you ever just sat down in your shop and looked at something ( a boat, engine or whatever ) for 10 or 15 minutes and thought how to make it better or to run faster? I started flying model airplanes in competition when I was 12 years old, and I would pick up an engine with a prop on it and just start flipping the prop over and over again thinking about what I could do to make it go faster. My Dad would always catch me and say " put that down, you're gonna wear it out". I have come up with a few ideas over the years that have been successful, but there have been MANY more that did NOT work out. That's just part of the learning curve. If you stick with your idea on this carburetor thing you will eventually come to a conclusion about weather it is going to work or not. Many other factors will certainly be involved ( pipe, pipe length, propeller, RPM, fuel pressure, intake velocity, among others ) to be successful with such a project. A lot of work and trips to the lake, for sure. Don't give up..........you will never know unless you try.

I still like to stick a toe "outside of the box" from time to time, but mostly now I just want to race and have fun!

Dick

 

[Nigtmare]

Hey Dick. The sure thing everyone knows how to do....It's the unknown that bugs the $hit out of me. :lol:

Terry Keeley has a good "Signature" That goes something like that!!!

" If you always do what you always did,

you'll always get what you always got..."

I'm going back too my sandbox.

Nick

 

[Charles Perdue]

Don't let the NAY SAYERS discourage you. If everone listened to them we would still be in the Dark Ages. Outside of the box? What Box? Work on your ideas until YOU are sure that it can't be done.

 

[Joe Warren]

Hey Nick,

Most of us "old farts" like to hear about others doing a little thinking "outside of the box" ( like Don always says ). Have you ever just sat down in your shop and looked at something ( a boat, engine or whatever ) for 10 or 15 minutes and thought how to make it better or to run faster? I started flying model airplanes in competition when I was 12 years old, and I would pick up an engine with a prop on it and just start flipping the prop over and over again thinking about what I could do to make it go faster. My Dad would always catch me and say " put that down, you're gonna wear it out". I have come up with a few ideas over the years that have been successful, but there have been MANY more that did NOT work out. That's just part of the learning curve. If you stick with your idea on this carburetor thing you will eventually come to a conclusion about weather it is going to work or not. Many other factors will certainly be involved ( pipe, pipe length, propeller, RPM, fuel pressure, intake velocity, among others ) to be successful with such a project. A lot of work and trips to the lake, for sure. Don't give up..........you will never know unless you try.

I still like to stick a toe "outside of the box" from time to time, but mostly now I just want to race and have fun!

Dick

NICk Dick is saying Good to think outside of the box!! But don`t lose sight of the BOX..... :lol: :lol:

 

[Nigtmare]

Okay...you have to look beyond the wood. Sorry I didn't put the spray jets on! :lol: I made this thing out of wood just to convince myself that it can be done. I've only used a file drill and a saw....and it looks it! :lol: If, hypethetically speaking, each barrell is 9 mm, a total of 18 or whatever you like to have, the secondary barrell will be fed by fuel a quarter way through the throttle travel. Anyway, I guess my next step is to take this thing and get someone to make it with different barrell openings. Now where's my BFH? I need to adjust this thing a little!