Carb help? Show me the ropes

[Defiant]

Sorry but I am correct CV stand for Constant VELOCITY.....The slides are operated by vaccum but it is the air speed(velocity) thru the carb that justifies and determines how far they open they are spose to be more economic and smoother and were designed to be used in all elavations on bikes(ie countries) because they compensate for different air pressure and atmospheric conditions without major tuning(in most cases)......have dout and tuned these carbs for more than a few years.

[SOHC]

hey people.

I have been looking at my bike and thinking that it would look way better with the AIRBOX off...

So here I am reading up about carbs etc.

I have a GB250 with a keihin VE carb. which is quite hard to get guff on till I found that Harley Davidsons use the same style.. learned a whole bunch really fast.

I also discovered the "choke" circuit in my carb was staying open due to the cable being sticky... Now I understand why it was being erratic. every start up was different.

So I am going to get a few different main jets etc and get tuning...

Also I made a mod to the pilot jet screw adjuster. on my carb and the harley version the screw is under the carb at the engine end. READ, hard to a screw driver in there, actually you can get a normal one in there at alll....

I made a knob on the lathe and soldered it on.... looks really good!

Any body want one. I will put up a post and pic of it soon.

Carbs...

R.

[pete376403]

Sorry but I am correct CV stand for Constant VELOCITY.....The slides are operated by vaccum but it is the air speed(velocity) thru the carb that justifies and determines how far they open they are spose to be more economic and smoother and were designed to be used in all elavations on bikes(ie countries) because they compensate for different air pressure and atmospheric conditions without major tuning(in most cases)......have dout and tuned these carbs for more than a few years.

Carb experience? Ok let me say "me too"
I'd beg to differ on the constant "velocity" - you say the air speed is the same regardless of throttle opening? Also - it's not the air speed through the carb that determines how high the slide lifts - the vacuum on above the slide determines this. And this in turn controls how much air (and thus fuel) goes into the engine. This idea has been around for many years, starting with the SU carb. Stromberg called them CD (ie constant depression) which is another way of saying vacumm, but certainly ot another way of saying velocity.
Wiki says this: Variable-venturi, in which the fuel jet opening is varied by the slide (which simultaneously alters air flow). In "constant depression" carburetors, this is done by a vacuum operated piston connected to a tapered needle which slides inside the fuel jet. A simpler version exists, most commonly found on small motorcycles and dirt bikes, where the slide and needle is directly controlled by the throttle position. These types of carburetors are commonly equipped with accelerator pumps to make up for a particular shortcoming of this design. The most common variable venturi (constant depression) type carburetor is the sidedraft SU carburetor and similar models from Hitachi, Zenith-Stromberg and other makers. The UK location of the SU and Zenith-Stromberg companies helped these carburetors rise to a position of domination in the UK car market, though such carburetors were also very widely used on Volvos and other non-UK makes. Other similar designs have been used on some European and a few Japanese automobiles. These carburetors are also referred to as "constant velocity" or "constant vacuum" carburetors. An interesting variation was Ford's VV (Variable Venturi) carburetor, which was essentially a fixed venturi carburetor with one side of the venturi hinged and movable to give a narrow throat at low rpm and a wider throat at high rpm. This was designed to provide good mixing and airflow over a range of engine speeds, though the VV carburetor proved problematic in service.
So we'll have to agree to differ on this.
However I believe the real place you'll find CVs is the drive shafts of front wheel drive cars .

[Defiant]

http://www3.telus.net/dougsimpson/CVcarb.html

http://www.google.com/search?rls=com...velocity+carbs


Well.....looks like we do disagree...I have no interest in turning this thread into a "i know more than you" thread........take a look at the sites above(i rest my case).....do your own search if need be.....I have worked with bikes and cars for more that 15 years and have my company of customers that have never been mislead so what you seem to know interests very little....I was merely offering to help the thread starter.......next time you see me on the road lets see whos carbs are better tuned huh?.........PS, i dont remember saying the air speed was constant and you who types so much should know that even a cv carb has a butterfly that is cable operated.......the vacuum you speak of is created by the air velocity(air speed) running past the rear venturi and causing negative air pressure(low air pressure/vacuum) resulting in the slide lifting thus opening the slide which in turns lifts the NEEDLE jet to deliver fuel from the fuel bowl via the EMULSION tube....otherwise know to the LACKY'S as the fuel jet......HD also refer to their own carbs as being constant velocity carbs as do hitachi, mikuni, Zenith and a host of others.......by the way CV in a front wheel drive vehicle is ALSO named as a constant velocity joint........I do need to comment that your response greatly reflects something i have seen on another carbs site.....????....i hope you didnt copy and paste....