accelerator pump doesn't spray...

I've recently bought a 2002 426 and rode it 7 times. It's my first 4-stroke dirtbike.

After adapting to the bike (haven't raced dirtbikes for seven years...been doing roadracing) and setting up the suspension I'm getting back to some decent riding.

Anyway. Now I noticed the bike doesn't take off when I pop the throttle wide open it just dies and takes off again when I give delicate throttle and even completely stalls when I crack it open in neutral...It almost threw me of after cracking it open after a turn folowed by whoops. :applause: Not good.

So I took the bike apart.

I noticed there's no spray into the carb when I open the throttle. I presume fuel should spray out off the brasscoulored jet...

Any ideas what to check, clean or replace??? It looks like a pretty complex carb...

GRtz from Belgium.

Take off the side cover (black plastic) and look for the little metal verticle pin towards the back. This is the rod that pushes the pump diaphram. Make sure it moves when you open the throttle. I've had dirt get packed in there and slow things down. Also you may want to remove the pump diaphram cover. It's the roundish cover at the bottom held on by 3 allen head screws. Make sure there's no junk on top of the diaphram and that there's no holes in it and the spring is OK. Finally you may want to put some cleaner or air through the holes by the diaphram and make sure the passageways are unblocked so gas can flow. I hope this helps and let us know what you find!

Look for the dirt build up Sir Thump mentioned first. It's pretty common.

The accel pump is a simple diaphragm pump. The discharge stroke is provided mechanically by opening the throttle, so that much is reasonably dependable. But the intake stroke of the pump is dependent on the return spring under the pump cover, and if the shaft gets bound up with crud, it can just stay stuck in the discharged position, never refilling itself for the next shot.

As mentioned, the diaphragm could be torn.

Additionally, there are two check balls involved, located in the float bowl assembly, one on the input side, and one on the output side. If these get dirt lodged under them, the pump won't fill or pump properly.

Apart from that, the discharge passage can be plugged up somewhere along its length.

The bulk of this stuff can be accessed without removing the float bowl, much less the carb, so it should be easy to find and fix.

Tnx guys, I'm going to check this.

Back into the freezing garage... :applause:


I found out that the acc.pump rod doesn't return to it's original position because off dirt build up ( :applause: good thinkin' guys). I cleaned the diagram and the mechanismes under the plastic cover.

What's a good way to clean the shaft.

Should I take the lower part off the carb (float bowl) or can I run some cleaner and air up the shaft and blow dirt out off it while leaving the carb on the engine?


I cleaned everything.

The dirty shaft and dirty diaphragm are clean (rod returns properly now).

The floater bowl had almost no sand in it and I cleaned and blew all holes and jets.

Still doesn't spray.


@grayracer: what's a 'discharge passage'? (I'm Dutchspeaking and don't know all the technical slang...)

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