off idle bog revisited.............

7 replies to this topic
  • yamahasocal450

Posted September 14, 2003 - 10:14 PM


has anyone truely solved their bog problems... well i did some researchin and saw that theres 3 ways to adjust it... the leak jet, new accelerator pump diaphram assembly, and the ap timing screw. i was in the dealer one day and the service man said that there was a bog and bla bla bla and said he could fix it for a rejet for 150 bucks.. um yeah right to change a jet.. i think ill do it, so i asked him if it needed a one size smaller leak jet (62) to run right then he was like yup but not a very good answer... now for the ap diaphram... there are 3 kinds, the one on the yz i think is smaller making it shoot a thinner squirt of gas maybe :) not sure on this and the screw might help a little but i didnt find it too helpful :D im going to solve the 450's jetting after i get the ktm worked out :D

  • GrahamO

Posted September 15, 2003 - 07:06 AM


Are you talking about initial throttle blip from idle stalling the engine. If so, I share your determination here. The timing screw hasn't produced any changes for me yet. I've gone a full turn in each direction with no results. I could make it worse, but not any better. I was focusing on the leak jet (which I believe would have the same effect as a smaller diaphram).

  • yamahasocal450

Posted September 15, 2003 - 09:16 AM


grahamo, do you think a bigger or smaller leak jet would be better? i think its being caused by a rich mixture so a 62 leak jet might solve it :) if this doesnt solve it fully i might either get the yz diaphram or a even smaller leak jet, or maybe i need to go up on the leak jet size because the yz's come with a 72 leak jet while the wr is stock with a 65 :D

  • GrahamO

Posted September 15, 2003 - 10:48 AM


From what I've read, the bigger the leak jet, the more fuel from the accel. pump is sent back to the fuel bowl. To lean the squirt you'd want a bigger leak jet. I'm headed out of town for the rest of the week, or I'd offer to be the guinea pig and give the YZ leak jet a try. You up for the challenge? :)

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  • yamahasocal450

Posted September 15, 2003 - 12:09 PM


i just a little more research and read that if you remove it the bike will run better than ever :) i'll try this the first weekend of october but if it doesnt work then i'll move to the yz jet :D :D

  • GrahamO

Posted September 15, 2003 - 12:54 PM


Depends on how you ride. Removing the leak jet completely allows all the fuel from the AP to bypass the squirt leaving you with NO squirt.

If you keep in the upper 1/3 of your RPM range (eg racing) then the AP doesn't do as much for you. In fact, it will add extra fuel, leaving you with a rather rich condition. That's why 400/426 racers would limit the duration to .3 seconds with the BK mod, and is probably why the YZ450s have a larger leak jet.

For the rest of us, those who frequent lower RPM ranges, the AP squirt is necessary, or we'll still bog, but this time from a momentary lack of fuel when we crack on the gas after the slide has been closed (slide closed, no vaccum; no vaccum, no fuel from jets). That's why .5 - 1 second duration is recommended for the rest of the mere mortal 400/426 riders, and why the WR450's have a smaller leak jet.

You can give it a try, but you'll find that stabbing the gas is still going to kill it. When I get back next week I'll give a larger leak jet a try.

  • Taffy

Posted September 16, 2003 - 05:18 PM


try dropping the needle once and then once again if that starts to help. if the MJ is over 165 drop it 5 and re-raise the needle 1.

that should do it and the tests are free.


  • yamahasocal450

Posted September 16, 2003 - 05:47 PM


taffy, ive got a 152 main jet and everything stock, ill try that first though, nothing beats free :)


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