'01 YZ426 carb questions x2

3 replies to this topic
  • MiGkillr

Posted March 13, 2013 - 03:31 PM


Okay, so I got the three valves replaced and the motor put back together, new cam chain, timed properly and rebuilt the carb per instructions with a new accelerator pump, all new jets, needle valve, gaskets, etc...etc...

I put the carb on the bike and kick it over a few times...yay! Compression is back, but no starting. Looking at the carb and cracking the throttle, I dont see the acclerator pump squirting. Not optimal. It was pulsing fine before the rebuild even with an accelerator diaphragm that looked like shredded lettuce. Thank you, gubment for the nice ethanol in the gas. I took the carb off and rechecked the accelerator pump. Diaphragm is on the right way with button facing the spring and new spring...two new O-rings. I didnt replace the pushrod because the old one was fine and moved freely. The length is the same. What gives?

I thought it might be a float problem (grasping at straws) so I decided to try a float adjustment. Obviously, I dont understand what "take a measurement when the needle valve aligns with the float arm" means in the manual. I bent the tab up to do what I thought was right. By "up, I mean toward the bottom of the bowl as I was holding it upside down when working on it.

Put the carb back on, attached all the bits. Still no start, still no accel pump squirt but plenty of fuel leaking out of a vent line.....oh, for joy. Thats gotta be a bad float setting.

Someone please educate me before I self induce more maladies.



Edited by MiGkillr, March 13, 2013 - 03:33 PM.

  • grayracer513

Posted March 13, 2013 - 04:12 PM


You're not supposed to hold the carb upside down while measuring. The right way is to tilt it from upright so that the float slowly "rises" on its pin until it stops against the spring pin in the needle. The measurement, then, is taken at the point where the needle "just touches" the seat, with not even the weight of the float on it. Your float level is way too high if set as you described.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • MiGkillr

Posted March 13, 2013 - 05:48 PM


Any ideas on the accel pump? My manual says to start off upside down, thus the issue. I'll try again.

  • grayracer513

Posted March 14, 2013 - 06:56 AM


Look at page 4-12. It does say to hold the carb upside down, but the next thing it says is to "slowly tilt the carb" until the float "aligns with" the float arm. Something you have to remember when working with any Japanese service manual is that translating Japanese to English doesn't always work very well, and you're quite often going to have to figure out WTH they were talking about when they wrote some of this stuff.

The needle has a compressible, spring loaded pin that helps it seal under conditions of high levels of vibration. The folat height is supposed to be set at the point where the float needle just contacts the seat , NOT when it's compressed to any extent. Doing it from upside down, you need to take the measurement right at the point where the spring pin becomes completely unloaded and any further tilt would separate the float tab from contact.

There is not very much that can go wrong in an accelerator pump, but its operation depends on a few things besides the rod being free and the integrity of the diaphragm. You need a clear fuel path in and out of the bowl through the pump cover. Buy a small plastic basting syringe intended for basting under the skin of a turkey at a grocery store, or any other such instrument. Fill it with solvent (gas is dangerous) and use it to test the circuit. With the float bowl off and the pump assembled, you should be able to push liquid through from the pump intake port in the float bowl, through the pump, and out the discharge port on the bowl flange. You should not be able to pump fluid backward through the pump from the discharge port, though. You should also be able to pump fluid from the point on the carb body where the discharge port continues and have that come out through the nozzle in the bore. Of course, filling the bowl and operating the pump with a flat ended pin should produce a squirt from the bowl flange.

If the second test fails, it's a simple obstruction. If the first test fails to show a clear, one-way fuel path, and the pump won't operate, check the two check balls in the circuit to see they are free and clean. These allow the pump to draw fuel only from the float bowl and discharge it only out the outlet side.

Related Content


Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  131 replies

100 hrs on 2014 yz450f, shim valves or replace them? by ttr230rider6

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  79 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

Need help by Goforaride

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  68 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.