Stalls on hard acceleration from idle.

[dslavik]

I just went out for the first time in several years.  I cleaned the carb and my only issue now is when I give it a lot of throttle off idle, the engine will stall.

 

If I slowly increase the RPM's everthing is fine.

 

What do I need to be looking for to fix this?

 

Thanks,

[Jim Dettman]

Something in the accel pump circuit is not working.  Either:

 

1. Diaphragm is torn

2. Internal passage is plugged (AP can't fill with gas).

3. Outlet nozzle in the carb throat (venturi) is plugged or corroded.

4. AP timing is off.

 

  Put a mirror in the air box with the filter removed.   When you wack the throttle open, you should see a good strong flow of gas into the carb.  If not, then it's one of the above.

 

Jim.

[badlogic]

I just went out for the first time in several years.  I cleaned the carb and my only issue now is when I give it a lot of throttle off idle, the engine will stall.

 

If I slowly increase the RPM's everthing is fine.

 

What do I need to be looking for to fix this?

 

Thanks,

sounds to me like the pilot jet is plugged. or you need a new accelerator pump

Edited May 19, 2014 by badlogic

[dslavik]

When I pulled the carb, everything in the accelorator pump seemed ok, it was getting fuel, the diaphram was not hard or cracked.  I didn't make any adjustments to the pump timing.

 

If the pilot jet is plugged, wouldn't the bike have trouble idling?  It starts and idles fine...

 

[Jim Dettman]

If the pilot jet is plugged, wouldn't the bike have trouble idling?  It starts and idles fine...

 

 

 Yes it would.  If your idling OK and a slow roll on of the throttle is OK but not a fast one (which you said), then the only thing it would be is the accelerator pump.

 

Jim.

Edited May 19, 2014 by Jim Dettman

[dslavik]

Thats what I thought.

 

It does feel like a timing issues.  How is this adjusted?

[Jim Dettman]

It does feel like a timing issues.  How is this adjusted?

 

 Just to be clear, we are talking about the timing of the AP, not the ignition timing.

 

 The AP is designed to deliver a strong squirt of gas when the throttle is opened suddenly.  You want the squirt to just miss the slide.  The adjustment is under the throttle cable drum cover on the carb.

 

 In this picture (click on it to make it bigger):

 

 

 

, it is the small screw  in the middle just below the large round object, which is the throttle cable drum.   This picture btw shows two carbs.  The one on the left is the old style AP linkage design and the one on the right is the late '08 and up redesign (removed the need to make the "O" ring mod or use a stiffer spring).

 

 On some models, the screw resides inside a cylinder and has a special head so it's "non-adjustable".

 

 You turn the screw to adjust the AP timing.  Nice video posted on TT of the testing and adjustment, but I don't have it handy at the moment.

 

Jim.

Edited May 19, 2014 by Jim Dettman

[dslavik]

Thanks for your isight Jim.

 

is it possible to replace the AC pump linkage with the newer linkage?  My bike is an 05.

[spaceboy]

Thanks for your isight Jim.

 

is it possible to replace the AC pump linkage with the newer linkage?  My bike is an 05.

http://www.crfsonly.com/catalog/product_info.php/cPath/138_147/products_id/3932

[dslavik]

http://www.crfsonly.com/catalog/product_info.php/cPath/138_147/products_id/3932

So this will solve the problem on my 05?  If i install this will there still be the need to do the O-Ring mod on the top part of the carb?

[spaceboy]

So this will solve the problem on my 05?  If i install this will there still be the need to do the O-Ring mod on the top part of the carb?

The 1st link was for the upgraded AP parts. Yes you would still need to do the o-ring mod(or safety wire) unless you replace the spring with a stiffer one like the Merge or the Tokyo mods spring.

http://www.crfsonly.com/catalog/product_info.php/cPath/138_147/products_id/4497

Edited May 19, 2014 by spaceboy

[Jim Dettman]

Thanks for your isight Jim.

 

is it possible to replace the AC pump linkage with the newer linkage?  My bike is an 05.

 

 No.   I'm not aware of any source for the internal parts on the carb.  You should do the "O" ring/safety wire mod, or better yet, purchase a stiffer spring for the linkage (the O rings and safety wire have a tendency to break).

 

When I talk about the linkage, I'm talking about the setup around the adjustment screw.  If you look at the photo on the left, note that the black arm (which is connected to a rod that pushes on the AP diaphragm) contacts the screw on the left and the head of the screw is on the right in the old design.

 

 In the new design, it's reversed; arm end is on the right, screw head is on the left.

 

The linkage rotates clockwise to activate the AP, so in the new design, the screw pushes against the arm.  In the old design, it pulled away from it, which is why you wired the two together or needed a stiffer spring.

 

Jim.

Edited May 19, 2014 by Jim Dettman

[BolinJrsPit Crew]

Probably the small passage after the ap diaphragm. Check for a squirt of fuel first. Lift rear subframe and twist throttle while looking through carb with a flashlight.

[FORMA MOTO]

The stock check ball in the apump / bowl cover gets corroded too........

[crazybrother]

The stock check ball in the apump / bowl cover gets corroded too........

+1 on that and if you install the Newer style A/C pump make sure to remove the check valve in your old float bowl. (the new one is built into the A/C pump). ?