Float Bowl AP Passage Check Valve?

I am working on my '98 wr400.  I have no AP squirt.  I have checked all of the passages and are clear, with the exception of the float bowl to AP passage.  I assume that it has a check valve in it: 1. because it would need to flow one-way from the pump to work and 2. there is a brass plug. So here's the question; is the valve normally open and it closes from diaphragm pressure or is it closed and the diaphragm pulls fuel in?

 

The diaphragm pulling the fuel seems unlikely, but if I fill the bowl with carb cleaner it does not run out.  If I plug the port with the tube of the carb cleaner can and spray it sprays out.

 

Does anyone have any experience with this?

Edited by tcmII

there is no valve.  There is a leak jet.  It "leaks" fuel back into the bowl.  so the ap squirt is actually going into the carb throat and the bowl.  change the leak jet to change that proportion.  With the carb assembled, does the ap work?  can you see a jet of fuel when you whack the throttle?  You can do this off the bike, and just turn the wheel, just dont squirt yourself in the eye...

 

also, PICS!

98 doesn't have a leak jet. Just a hole to allow the ap bowl to fill.

So I'm back to this.  I am looking at the passage from the float bowl to the AP.  I agree that there is no leak jet, so for the AP to work there must be something to temporarily block the inlet passage or it would just pump the fuel back into the bowl.  When looking at the AP inlet from the bottom bowl view you can see a pressed in brass "plug" it would seem that this either provides some restriction or holds  a check valve.  The plug does not seal 360 and has small gaps,. I need to understand how it's supposed to work.  If I remove all of the AP parts and fill the bowl and wait it does not drain out. 

 

Options:

1. brass plug is intended to provided a restriction, similar to a leak jet, and is clogged

2. brass plug holds in a check valve (have seen something similar to plug cross drill passages)

 

Here are the pictures

 

 

 

 

Bowl Inside View.jpg      Bowl Bottom.jpg

 

Edited by tcmII

Yes there is a BB and a passage under that plug. It's a bad design cause they corrode all the time.

Soak it in strong solvent.

That is what I guessed based on other carbs.  As I work on getting it cleaned, should I expect that the BB will get loose enough that it would rattle when clean?  I have been able to make it dribble using a very fine wire, but not enough to be proper flow.  I have also though of adding a hole or two on the outside edge of the brass plug with a wire drill to get more flow.

Just use a syringe and carb cleaner, or a WD40 / Brake cleaner can and use the pressure to slowly clean the passage.

I had a blocked AP circuit on my 400f and it took a week of spraying but it finally came clean.

That is what I guessed based on other carbs.  As I work on getting it cleaned, should I expect that the BB will get loose enough that it would rattle when clean?  I have been able to make it dribble using a very fine wire, but not enough to be proper flow.  I have also though of adding a hole or two on the outside edge of the brass plug with a wire drill to get more flow.

 

It takes time. You have to soak it. Don't be tempted to 'push stuff ' inside there, you will just do damage.

No, it will not rattle.

Ok, after waiting 2 weeks for the dealer to get the parts, I have replaced both o-rings, the AP diaphragm and the bowl gasket. Checked that all linkage is working properly. Hook fuel line up to the tank to fill the bowl with fuel and look for the AP squirt - no joy!  Tried twice.  Drained bowl and removed AP cover.  AP bowl and diaphragm is dry, no fuel.  Hooked up carb to tank with AP bowl removed and turned on fuel, nothing is getting to the bowl.  If force the nozzle of a can of carb clean into the float bowel side of the AP passage the cleaner will flow through.  So it works under pressure.

 

So I'm back to these questions:

 

Should fuel flow from the float bowl to the AP bowl due to gravity?  Seems like the answer should be yes.

 

If fuel does not flow due to gravity, how does I get filled?  For the AP diaphragm to pull it in there would have to be a check valve between the AP bowl and the AP nozzle in the carb.  This does not appear to be the case.

 

I getting to the point where I may need to but a new float bowl from Sudco.  That's a very expensive experiment.

Finally all is working properly.

 

 

 

Thanks to James Dean for the best information, once I got ahold of him I solved the problem later that evening.

 

After weeks of waiting for parts and some misleading information  here's what I learned:

  • There are TWO check valves in the AP circuit on the Keihin Carburetor.  One in the float bowl and one in the upper carb body.  The AP diaphragm draws fuel through the check valve in the float bowl and pushes fuel through the check valve in the upper carb body.
  • Fuel will NOT flow through the float bowl due to gravity.
  • NEVER disassemble the upper carb body, there is on replacement gasket available (I did not do this, but this was the one consistent bit of info I received)
  • Make sure all of the passages are clean and the check valves are working properly.
  • Call James Dean first. (Not a knock, I did email but didn't get a reply so I didn't call right away. That cost me a lot of wasted time and effort)

 

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