Re: Pumper Carb?
Originally posted by HomeMadeSin
Thanks for the info. BTW, what is a pumper carb? Maybe I've been out of it for a while, but I have never heard of it.
Here's the info from stroker. From personal experience, these carbs really make a difference on XR's and KLX's.
What is the difference between a "cv" constant velocity type carburetor and a "pumper" carb? What about other after market companies selling "flat slide" two stroke carbs? They are cheaper, but how do they work?
Most fourstrokes come with a constant velocity carb on them. The way they work is when you twist the throttle, the slide doesn't go up. Instead a butterfly opens and allows for fuel to enter the motor. Once the motor builds up pressure, the pressure raises the slide. This is why the "CV" type carbs have no bottom end throttle response. There are other after market companies that sell "flat slide", two stroke carbs as a replacement to the "CV" type. The problem with the "two stroke" carb is that it doesn't have the fuel circuits needed for a fourstroke. The result is that you will have better mid and top, but the bottom throttle response will be worse than the "CV" type. At Stroker, we have put "accelerator pump" carbs on fourstrokes since we have been in business. People thought we were crazy. What these people didn't know, was that they have been in use on fourstrokes before we did it. Just no one put them on off road bikes, except us, until the new YZF400 came out. Now that the YZF400 pumper carb works so well for that bike, and comes from the factory like that, those people that thought we were crazy, are now using pumper carbs. The reason the manufacturers use the "CV" type carb, is because it is user friendly and is not as sensitive to elevation changes as the "pumper" carbs, and it's cheaper to make them. Sometimes cost is an issue when manufacturing a motorcycle. For performance, there is not a carb out there that will beat a "pumper" carb. We have seen more and more "new" fourstrokes coming out with pumper carbs on them. A pumper carb works like this. When you twist the throttle, the slide raises up, and an injector squirts raw fuel in the head. (Just like a fuel injector )This is where you get your instant throttle response with this carb.
It says here pumper carbs are more sensitive to elevation changes, I've ridden from Kennedy Meadows @6-7,000 feet and Big Bear at 4-5,000 to where I usually ride at 1,500 - 3,000 ft. I have the jetting set up for roughly 3-5,000 feet and it's worked pretty well at those other elevations.
