KDXRIDER.NET

http://www.motorcycle-superstore.com/21 ... rator-pump
And what does it do?

It is a device that delivers a squirt of fuel to a thumper when quickly opening the throttle...

Accelerator pumps are for 4 strokes. It helps get the gas into the bike when cold.

ok thanks!

Oddly enough, way back in 1981, there was an aftermarket accelerator pump marketed for use on both 2 and 4 stroke motocrossers. Dirt Bike magazine tested it on a 2 stroke and liked it, so I tried one on my then 3-year old '78 Yamaha YZ125. It was a bit crude, but very impressive.

You know how a 125 will bog out if you whack the gas wide open at low rpm under load? Mine would just pull hard and clean from off idle -- in any gear -- to red line with the accelerator pump. Normally I had to do race starts in 1st gear; with the pump, I could do them in 2nd all day, and sometimes 3rd! With a 125!

Unfortunately, I was testing with a worn piston & rings ( I was a broke college student ) and during one of those 3rd gears starts, blew the rings into the pipe, wiping out the cylinder. I never got to try it in a race.

I still have that accelerator pump, and I'm gonna try it on my 220 when I get a chance............

You can still get carbs for 2 strokes with a fitted "power jet" basically fuel is drawn from the float bowl via a tube & squirts gas into the rear of the carb which gets drawn through at hi RPM.... I owned a Yamaha RD 350LC with a set of these carbs fitted & the bike ran very well indeed .

I have never seen a accelerator pump for a two stroke not saying they don't exist. Back in the day I worked on/with plenty of power jets on two stroke carbs. As said they usually hang down just befor the slide. They are controlled by a tube from the bottom of the float bowl which can have a narrower or wider Ida to determine the amount of draw/vacuumed required to pull fuel out. Jets in line will determine how much can be drawn. If you have elotronics a solenoid will do the on off for you and jets how much. They are generally to tailor top end jetting for motors that are head flat out for lengths of time like road racing.
Accelerator pumps on the other hand are for low revs where a sudden wide open throttle gives the motor a big gulp of air and the normal vacume jetting can't deliver fuel in enough quantity so you get a bog. The power jet squirts in fuel to fill the hole and this means sudden kick instead of bog.

Yep, this was an accelerator pump, not a power jet. No matter how fast I whacked the throttle open, the bike would not bog. Keep in mind this was a 125 motocrosser. It didn't increase top end power at all, just made the bike easier to ride. At higher rpm, throttle response was noticeably better. I'm still surprised accelerator pumps haven't been factory equipment on 2 strokes.

I'll try to put up a pic of this thing if I can find it.

Because the low end circuitry of newer 2-T carbs has gotten so good it's unneeded. Put a Mikuni VM on your KDX and you will lose this. It was probably sweet to just get a squirt of fuel, and not have to mess with jetting as critically.

That's a good point; the carb on that 125 was a Mikuni.