'06 YZ450F; Snap Accel Kills It, Help!


11 replies to this topic
  • N6965F

Posted July 14, 2013 - 01:56 PM

#1

2006 YZ450F. Until about 4 rides ago. the bike ran perfectly. Couldn't kill it no matter how quickly you snap the throttle off idle. Now it dies and/or pops hard out the silencer (after fire) when snapping the throttle off idle. Idles fine, top end power is great. I did replace the air filter about 4 rides ago, but with the same make and style (TwinAIr).

Carb has several mods, and I have no reason to question them or the jetting as the bike performed great until recently. I believe the previous owner had "zipty" style mods installed.

Trouble shooting steps taken:
-Checked valve clearances, spot on, have not changed in 15 hours.
-Thoroughly cleaned carb, several times
-Replaced hot start plunger and cap o-rings
-Replaced pilot screw o-ring
-Inspected accel pump, no squawks noted
-Checked the function of the accel pump, appears to be OK.
-Ohmed out all electrical, including TPS, all coils, and neutral switch, no squawks
-Replaced spark plug with new, gapped per manual
-Unplugged TPS, no change in accel performace
-Performed "by ear" adjustment of pilot screw, idles great at 2.5 to 1.5 turns depending on temp

Next Steps I plan to take:
-Repack silencer. Its very loud, and maybe its lacking back pressure? Any thoughts?
-Reduce the size of the Leak Jet, currently stock #55.

Any help is greatly appreciated.

-Joshua

  • grayracer513

Posted July 14, 2013 - 03:54 PM

#2

If the bike ran fine in its current configuration, why would you change the size of a jet. The muffler isn't the problem, either.

More than likely the carb. If it sat for a week or two in the heat, you might have a varnished pilot jet. Check it.

http://www.thumperta...726#post8021726

Also check the vacuum release plate on the engine side of the slide to be sure it isn't cracked or missing a corner. Check the seal between it and the slide, too.

  • gscx

Posted July 14, 2013 - 03:57 PM

#3

Does Ziptye use a o ring for the accelerator pump? If so the oring could have broken from age.

  • grayracer513

Posted July 14, 2013 - 05:21 PM

#4

I think that at one point they were including the O-ring trick with the main air circuit mods. The failing O-ring is one reason I don't recommend it, instead pointing people toward a heavier linkage spring like the one from Merge Racing.

  • N6965F

Posted July 14, 2013 - 06:13 PM

#5

If the bike ran fine in its current configuration, why would you change the size of a jet. The muffler isn't the problem, either.

More than likely the carb. If it sat for a week or two in the heat, you might have a varnished pilot jet. Check it.

http://www.thumperta...726#post8021726

Also check the vacuum release plate on the engine side of the slide to be sure it isn't cracked or missing a corner. Check the seal between it and the slide, too.


Yes, this is the information I was looking for. It did sit for a while, in 100+ degree weather in my garage. I will pull it apart tonight or tomorrow, and post my results.

Thank you.

-Joshua

Edited by N6965F, July 14, 2013 - 06:18 PM.


  • N6965F

Posted August 11, 2013 - 06:04 PM

#6

Replaced pilot jet with new one of the same size. Performance did not improve.

Pulled carb. Inspected vacuum release plate, no defects noted. Replaced seal on vacuum release plate, performance did not improve.

Pulled carb again. Replaced all seals and changed the carb to head boot/ intake manifold. Performance did not improve.

So now what? Is there a chance one of my cams jumped a tooth? What about ignition timing?

Anyone in the Reno/Tahoe area in the market for a YZ450F? Make me an offer, and I just might take it cause this thing has me pi$$ed off.

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

Posted August 11, 2013 - 06:47 PM

#7

Well have you checked to see if there is an old o ring around the accelerator pump linkage that is broken? Really this sounds like a AP issue

  • NitrousR1

Posted August 12, 2013 - 02:35 PM

#8

If the bike runs fine everywhere but snap throttle, This is a classic accelerator pump duration and/or squirt timing issue. The fact that yours was good means the leak jet/ pathway in the float bowl/ or ap nozzle could be restricted. You said the diaphragm looked ok. If it runs great elsewhere then leave the other circuits alone.
Start with removing the intake boot or gently push it out of the way so u can see the ap nozzle in the carb. With the fuel petcock on whack the throttle quickly and measure your squirt duration with a stop watch or ideally on video with slow mo. If the duration is too short or too long it will cause this bog. You want between a .5-1 second squirt.
To change it go with a appropriately larger or smaller leak jet. Yamaha actually makes different diaphragms with different sized rivets to decrease/increase flow. They put out a TSB- Technical Service Bulletin for this that I'd gladly look up for you.
I've got mine dead on and no bog no matter how fast or slow the engine speed is. Some people say it can't be done, but it can. The Yz/wr250f is notorious for this. Off the showroom floor they can have a Terrible bog and stall. I've recorded from .1 to 4.5 seconds of duration on brand new yz250f's. We fixed them before selling them but most dealers dont. same applies to the 450. There is a great sticky in the Yz/wr250f forum u should read up on.

  • grayracer513

Posted August 12, 2013 - 02:58 PM

#9

 Yamaha actually makes different diaphragms with different sized rivets to decrease/increase flow. They put out a TSB- Technical Service Bulletin for this that I'd gladly look up for you.

 

In Common Threads:

 

http://m.bobbitt.hom...fm/tech/ap1.jpg

http://m.bobbitt.hom...fm/tech/ap2.jpg

http://m.bobbitt.hom...fm/tech/ap3.jpg

 

Read the whole thing before jacking up the accelerator pump squirt volume to the point that it will take a snap open, but runs dirty through slow corners and stalls all the time. The pump timing adjustment procedure is listed in the manual.  Also read:

 

http://www.thumperta...f/#entry3596648



  • NitrousR1

Posted August 13, 2013 - 02:26 PM

#10

Whatever I can do to help. Take your measurement of the duration and I'll walk u through it

  • jwleonard

Posted August 21, 2013 - 01:51 AM

#11

I had a similar problem on my 98 400 and thought I had tried everything, I also had popping on deceleration too.  I had taken the slide apart and inspected the seal & corners of the vacuum release plate several times to include changing the seal even though there was nothing visually wrong with it.  Finally I found that the plate itself had a crack in it that could only be seen with pressure applied to it.  I replaced the plate (expensive if you buy new) & seal and the issue was resolved.  Also, you need to make sure the coating on the slide & plate isn't deteriorated since that can cause excessive air leaks too as the surface will be uneven. 

 

One other thought, have you tried removing the air filter (or the connection at the carb) and running it as a test (being very careful of course) to make sure it isn't made wrong and not allowing enough airflow.  It just seems strange that 4 rides ago you changed the filter & 4 rides ago you started having problems.



  • grayracer513

Posted August 21, 2013 - 06:39 AM

#12

Over-oiled filter, perhaps, or run too soon after oiling and sucked a blob of oil onto the air jets.

 

Along that same line, if you look under the filter of any later YZF like the '06, you'll see that the air boot is made so that it incorporates what is essentially a "velocity stack"; an air horn extension of a tuned length that funnels air only into the intake bore of the carb.  A separate air route for the main and pilot air jets in the mouth of the carb is channeled under the intake stack, and can be subject to blockage.  Could be that simple.

 

When oiling filters, assuming you oil them enough to be effective, it's always prudent to hang them over a can or something for several hours to drain off the excess into something besides the air box and the top of the swing arm.







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