Carb issues on '99 YZ400

4 replies to this topic
  • Pothole

Posted October 19, 2004 - 06:50 AM


Yesterday, my bike started bogging pretty bad when I'd crack the throttle open, a problem that I hadn't experienced before. I pulled the carb, cleaned it and blew out alot of the jet ports, and I did the Taffy Mod while I was in there. Before I pulled the carb off, I looked at the timing of the accelerator pump squirt, and it seemed like a good 3-4 seconds. I took the AP diaphram out and cleaned it and put that collar on the AP plunger rod, and now there is no squirt at all, even with the Taffy mod collar pulled off. The AP diaphram looked ok, a bit of rust on the top, but the diaphram itself looked good. Any ideas?

  • yzf_rider400

Posted October 19, 2004 - 09:55 AM


I'd say just clean it out the AP pump lines and reinstall everything again. Maybe you put the diaphragm in upside down?

What happenned to me when I cleaned my rod and diaphragm off was that I think I loosened some of the gunk and when new gas got in there it lifted it off and clogged a fuel passage. You probably just need to clean it out again.

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  • bushy

Posted October 19, 2004 - 03:56 PM


With the gas on and the line hooked up, twist the throttle many times. You have to prime the pump.


Posted October 20, 2004 - 05:41 AM


You did remember to reinstall the pump spring right?

Also be aware that if the very tiny o-ring washer falls out during installation it creates a venturi effect and the pump bleeds off and won't work either.

You should have 2 o-ring washers in the bottom cap.... 1- large and 1-very small in the pump cover.

Just Checking....

Bonzai :cry:

  • Pothole

Posted October 20, 2004 - 06:35 AM


Yep, got the o-rings and the spring installed. Although the bike started like a dream, it started on the first 1/3 of the first kick, even though it was totally flooded with gas from me watching how the AP was that's a good sign. However, what appears to be happening is when I open the throttle very quickly is the gas just kind of boils out of the jet. That seems like there is air getting in there? I've ordered a new AP diaphram, o-rings, and spring..hopefully that will fix this.

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