Sign in to follow this  
Followers 0
buzzfin

Accelerator Pump Problem

19 posts in this topic

Went out for a ride this weekend and couldn't start my 98 YZ400. Noticed that the shaft going into the accelerator pump was not moving down into the pump when opening the throttle. I have a new pump cover and diaphram, so no problems there. If I empty the float bowl and pump cover, the shaft moves fine. When I fill the float bowl and turn the throttle, the shaft stops moving - leading me to believe the port on the carb through which the pump squirts fuel is clogged. I pulled off the float bowl and verified the pump does squirt fuel when not on the carb. Tried cleaning the port by spraying carb cleaner (no luck) and then passing fishing line, and a small piece of wire into the port on the body of the carb that the acc pump sprays into. Wire only goes in about and inch and then stops. Where does this port come out in the body of the carb? Shouldn't I be able to clear this port easily using this method?

Share this post


Link to post
Share on other sites

If it's the same as my 2000 426 it comes out of a little brass protrusion that sticks up maybe an eighth inch into the bottom of the carb throat. It has a hole in it on the engine side so the stream is directed into the engine.

Share this post


Link to post
Share on other sites

There is a check valve to allow fuel to enter the pump housing, but not to back out, and another on the discharge side to allow fuel out, but prevent backflow. The discharge passage runs through the float bowl from the pump housing to the carb body, where, as said, it terminates in a brass discharge nozzle with the port facing the engine. If the nozzle clogs, you will almost certainly need to remove the carb to be able to clear it from the engine side.

Share this post


Link to post
Share on other sites

The carb is off but I can't get anything to pass through the nozzle from the engine side. I tried carb cleaner and compressed air - neither will pass through either end and the nozzle appears to be so small there is no way I'll get wire to pass through it. Should I try a small pin or needle? I don't want to damage the nozzle by trying to shove things inside it. Any suggestions?

Share this post


Link to post
Share on other sites
A pin or sewing needle, used prudently, should work.

Maybe tiny number drills....

Share this post


Link to post
Share on other sites
Maybe tiny number drills....
Number drills can be useful to clean jets with, but again, prudent use is mandatory. Be sure you only use a drill AS large as the orifice, and no larger. Just reshaping the entry/exit of the jet orifice can alter its behavior.

The hole in the end of the AP nozzle might even be smaller than a #80 drill, too.

Share this post


Link to post
Share on other sites

I used a sewing needle and only the tip was small enough. Seems to have done the trick though. I can now spray carb cleaner through that passage. Putting it back together to give it a try now.

Share this post


Link to post
Share on other sites

Got it all back together but it still won't start. This bike normally fires in 2 kicks. Only thing changed was adding a flexjet fuel screw. I put the stocker back in and set at 1.5 turns but no luck. I'm stumped!

Share this post


Link to post
Share on other sites

May sound like a dumb quesiton but you never know on the internet

You do have, from the bottom up, Spring/washer/o-ring right? I have seen people screw it up.

Share this post


Link to post
Share on other sites

The stock screw did not have an o-ring on it, but ran fine without it. I guess the previous owner removed or lost it?? I tried the new screw with the o-ring provided (in the correct order) and had no luck, so went back to the old stock screw with just the spring, no o-ring. I just pulled the spark plug and it looked pretty bad, so I put a new one in. Still no luck. Maybe I'll try the stock screw with the washer and o-ring now that the plug is new to see if that makes any difference. If that doesn't work then I'm thinking I might have to pull the carb (again) and clean all the jets. Frustrating since I just did that a few weeks ago...

Share this post


Link to post
Share on other sites

Better try again. You need the washer and O-ring. They may have stuck in the bore, though, which would help explain why you had trouble trying to install the screw with one.

Share this post


Link to post
Share on other sites

YOu may be doubling up on the washer and O-ring on accident. The o-ring will sortof "glue" the washer in frequently, and not come out. If that is the case, I bet the needle isnt sitting properly either when you bottom it out to adjust it out.

Id look closer in that area first.

Share this post


Link to post
Share on other sites

I checked and confirmed the old o ring is not stuck inside. I'll put the washer and o ring on the stocker and try again. Would the missing o ring keep the bike from starting at all?

Share this post


Link to post
Share on other sites

yeah, it could. It would seriously effect the mixture at the lower RPMs I am sure. Not saying it is your only prob, but it is a prob none the less

Share this post


Link to post
Share on other sites

Got out to the garage last night to work on the bike. I put the washer and spring on the stock screw, but it didn't help. Neither did fresh gas and a new spark plug. Finally figured out that the timing jumped a tooth. Not sure how that happened as the chain appears to be tight, the tensioner is in good condition and the gears appear to be okay too. The only thing I can think of is that I removed the tensioner for better access to the float bowl when I put in the aftermarket fuel screw. I'm thinking the chain must have slipped then.

Share this post


Link to post
Share on other sites
Got out to the garage last night to work on the bike. I put the washer and spring on the stock screw, but it didn't help. Neither did fresh gas and a new spark plug. Finally figured out that the timing jumped a tooth. Not sure how that happened as the chain appears to be tight, the tensioner is in good condition and the gears appear to be okay too. The only thing I can think of is that I removed the tensioner for better access to the float bowl when I put in the aftermarket fuel screw. I'm thinking the chain must have slipped then.

That would deffinately do it.

The only time you can safely remove the CCT and NOT risk jumping a tooth is at TDC, and even then it is recommended that you take some precautions, like zip tying the chain to the sprockets.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0