wondering if dual nt carbs is a good thing or not seen it on youtube looks cool but wondering if theres any disadvantages and if you gain anything
dual carbs
- Thread starter joelogger2
- Start date
I've never tried it but here's my opinion anyway. Other than the "Cool" appeal I doubt there would be any advantages. Especially where a stock, unmodified engine is concerned. The little Chinese 2 stroke can only handle so much fuel and air for proper combustion. Adding another carburetor woud require an extremely lean tune to both carbs and matching them would be critical.
You're also restricted to intake port area. You can only pass a given amout of fuel/air charge through that port. Doubling carburetor output won't change what the engine can use. You'll also have to get over the mechanical hurdle of controlling two carbs from one throttle. Not impossible but it would take some engineering.
Still, it would look really unique. Twin carbs and air filters sticking out both sides. Neat!
Let us know if you try it and take pictures.
Tom
You're also restricted to intake port area. You can only pass a given amout of fuel/air charge through that port. Doubling carburetor output won't change what the engine can use. You'll also have to get over the mechanical hurdle of controlling two carbs from one throttle. Not impossible but it would take some engineering.
Still, it would look really unique. Twin carbs and air filters sticking out both sides. Neat!
Let us know if you try it and take pictures.
Tom
the video that i seen on youtube the guy had two thumb throttles but i think i could make it work with a y cable like on some bike brakes but as far as getting the port to take more was i was thinking case induction and hog out the transfer ports as much as possible use a 7cc twin plug head from freds cr machine with hds lightnings twin ignition system lots of fuel and air lots of spark i wish someoone would come out with a forged piston with chrome moly rings for these things and a ultra light titanium rod and bad ass berrings and dont get me started how big of a joke these cranks are
With dual carbs on a single cylinder there's no need to synch the carbs, just get them close but tune them evenly so a simple cable splitter would work, but if you wanted to gain something from dual carbs it could be done better by using 2 smaller carbs to flow like a bigger carb, but it would take 4 14mm carbs to flow the same as a 28mm carb, dual 14's would flow about the same as a single 19 or maybe 20mm... the math is somewhere to figure it out more exactly.
how could running 2 14's benefit over a single 20? If one was to set them up to open sequentially or progressively instead of at the same time the effect would be similar to a modern 4 barrel carb on a V8 where you use the small side for cruising efficiency and better low rpm throttle response, then open it up more as the rpm goes up to feed the demands of the engine and make max power. If one was to run a progressive multi carb setup with maybe a 10mm primary and a 15mm secondary it would give stronger starts until the rpm comes up then the throttle could be opened up to bring the secondary into play for a strong top end.
It would definitely take some tinkering to get the air fuel mix right across the rpm range, but it could be done... Actually a better idea would be to set up a 24mm cv carb to run on your engine and set the slide rate so it never bogs, but not so slow the throttle response would suffer, that way you could crack the throttle right from the start and have the same good low end torque and smoothly transition to high top end power... Again, lots of tinkering involved but the outcome would be better than any multi carb setup, just gotta determine the right size carb you'd need for the best top end power and rpm, then get a few extra slide springs so you can play with higher or lower spring tension until it delivers smooth power. i'm sure there's a reason CV carbs aren't used on most 2 stroke engines, but it would be an interesting project for someone who has both the time and funding to try and get one to work right.
how could running 2 14's benefit over a single 20? If one was to set them up to open sequentially or progressively instead of at the same time the effect would be similar to a modern 4 barrel carb on a V8 where you use the small side for cruising efficiency and better low rpm throttle response, then open it up more as the rpm goes up to feed the demands of the engine and make max power. If one was to run a progressive multi carb setup with maybe a 10mm primary and a 15mm secondary it would give stronger starts until the rpm comes up then the throttle could be opened up to bring the secondary into play for a strong top end.
It would definitely take some tinkering to get the air fuel mix right across the rpm range, but it could be done... Actually a better idea would be to set up a 24mm cv carb to run on your engine and set the slide rate so it never bogs, but not so slow the throttle response would suffer, that way you could crack the throttle right from the start and have the same good low end torque and smoothly transition to high top end power... Again, lots of tinkering involved but the outcome would be better than any multi carb setup, just gotta determine the right size carb you'd need for the best top end power and rpm, then get a few extra slide springs so you can play with higher or lower spring tension until it delivers smooth power. i'm sure there's a reason CV carbs aren't used on most 2 stroke engines, but it would be an interesting project for someone who has both the time and funding to try and get one to work right.
Exactly... Time and money spent much better on a reed valve kit, some good porting and the right pipe in conjunction with the right sized single carb to match the other upgrades... Even with the right pipe and a good porting job, one can even stay piston ported and be very happy with the performance.Hmmm......would probably get more results with a port/reed valve kit.
Best of luck in your quest to go faster!
The best bang for the buck is still a good pipe for these engines, the porting can be done at home to save money and gain experience, or one can buy a good ported jug from a few of the better vendors in here with excellent results.
That's a push/pull throttle, it can actuate multi carbs that use a common shaft or a common throttle lever, but not 2 separate carbs with each cable. These throttle assemblies work by using one cable to open the throttle and the other to close it. This type throttle control is mandatory in most road race circuits because you can still close the throttle if a return spring fails or the throttle gets stuck open for any reason, and several bikes from the late 70's to present times use this type for that extra safety margin.
I've got a couple of these, and they absolutely could operate 2 separate carbs with separate cables. If you like I could post photos of the inner cable guides when I get home.
OK... I see it now... it just looked like a typical push pull type when I saw the pic this morning... and Yes, that type will work. So the bolts on the back side are for synch and friction adjustment?
Dave, I thought about a cv carb when I first got the engine, and realized it wouldn't work. CV carbs would go insane on a piston-ported 2 srtroke since part of the time the airflow is going the wrong way, there is no smooth vacuum to raise the slide so it would probably jitterbug all the time. Maybe with an intake reed....
The progressive dual carb setup sounds interesting, though.
The progressive dual carb setup sounds interesting, though.
Truthfully, it's a waste of time on a single cylinder engine to have more than one carb, the right sized carb with the right jetting will win every time. And I have converted real motorcycles from carb to fuel injection which is definitely the way to go, but I wouldn't waste my time or money trying to fuel inject a China Girl... but the idea of doing it on a Rotax does sound very appealing...
It definitely Can be done, but other than the uniqueness or the "it looks cool" factor, the same performancce (if not better) can be had by using the right sized Single carb with the right jetting inside.
