2006 YZ450 how to modify or improve accel pump ?

5 replies to this topic
  • Thesolidman1

Posted February 18, 2010 - 07:13 PM


Hi, I have a 2006 YZ450. I was considering the Zip Ty carb mod, but the bike runs quite well as is. I seem to recall some do-it-youself modification to improve the accelerator pump, perhaps wiring something or upgrading a part. Mine is stock, I'm curious what the hot tip is. Thank you in advance for your help.

  • grayracer513

Posted February 18, 2010 - 09:20 PM


If the pump timing is correct, and the carb is correctly jetted, AND you learn not to snap the throttle, it doesn't need improvement. Just my opinion, of course.

But if you insist...

There was a thread started in the CRF forum regarding wiring the AP linkage to prevent the damper spring from working, resulting in higher output pressure from the pump. This also requires that the stop button on the AP diaphragm be removed so that the solid linkage won't keep the throttle from opening fully, and that in turn requires a huge increase in the size of the leak jet to keep from totally drowning the engine. It's a cavemen approach to the problem, but it's made to order for someone who likes to sit on the line and crank his right elbow through sixty degrees like a dork (really sorry for offending anyone). Look it up.

Those who understood the shortcomings of wiring the linkage, but still thought the bike needed more squirt from the AP came up with the idea of using an O-ring to bind the two linkage arms held together by the linkage spring with a little more force while still allowing it to function normally. That means the stop button on the AP can stay put, and more realistic squirt duration timing can be had without using a leak jet larger than the main jet. This is a somewhat better approach, to say the least, and the only thing really wrong with it is that the O-ring may not last that long. Search for the "O-ring mod".

Merge Racing took the O-ring mod to the next level by making a stiffer AP linkage spring, making the use of an O-ring unnecessary while accomplishing the same thing, and is by far the best approach of the 3.

Most of the aftermarket pump covers available don't really do anything worthwhile. The only point of potential real improvement is the check valves in the cover assembly, which can be a little erratic in the stock unit. But they aren't usually a problem that most people would ever really notice. Special float bowls are a major waste. They're $100 platforms to put a $100 pump cover onto. Pump covers that allow external adjustability do make it simpler to correct for for a modified pump after the mod is done, but remember that once the leak jet is set, there is very rarely any reason to change it.

And again, in my opinion, most of the time, a legitimate bog can be tuned out with the adjustments available on the stock carb, and usually without doing very much to the AP at all. And, a lot of the time it ends up being a rider training problem more than it is a carb.

BTW, here's more on the subject of leak jets:


  • hillclimbguy

Posted February 18, 2010 - 10:22 PM


I'm with you Gray on this. If aint broke dont fix it. Mine and my sons YZ450s work just fine. Though my sons bike is way faster than mine, I've narrowed it down to him being just young.

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  • ThumperKid250F

Posted February 19, 2010 - 09:04 AM


i sent my carb to zipty a couple years ago and they did there thing to it and its awesome.. you can snap my throttle like a 2 stroke and it dont bog at all.. very good mod

  • JJRace

Posted February 19, 2010 - 11:55 AM


there is a jet in the bottom of the bowl you can change out. start there and the fuel screw.

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  • Ga426owner

Posted February 19, 2010 - 12:17 PM


another vote on ZipTy - they tuned my 06 carb perfectly. No more bog period. Too bad they could not get the same result on my 03....:ride:

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