2001 YZ426F Hanging idle

I'm searching for an air leak and I think I found one near the air boot from the filter to the carb. But I also noticed the exhaust gasket from the header to the midpipe is almost completely worn out. I can slip the midpipe off with the clamp tight. Would this also cause the idle to hang? Thanks in advance!

pull the slide out an check the vacuum plate the old fcrs were bad about cracking,they hang idle,then chip off an destroy the top end

But I also noticed the exhaust gasket from the header to the midpipe is almost completely worn out. I can slip the midpipe off with the clamp tight. Would this also cause the idle to hang? Thanks in advance!
No. It might cause decel backfiring, though.

For a hanging idle, check your pilot screw adjustment, check for external air leaks, check the vacuum release plate mentioned above, and check for tight intake valves.

No. It might cause decel backfiring, though.

For a hanging idle, check your pilot screw adjustment, check for external air leaks, check the vacuum release plate mentioned above, and check for tight intake valves.

Thanks. I went out and checked the plate, no cracks that I can see. I'm going to order a carb rebuild kit. I think the o-ring from the carb to the air boot transition is the culprit. It was wet when I pulled it out.

Anybody know where I can find the stock jetting specs? This is a friend's bike and I don't have a manual. I found a 168 main, 42 pilot, and OBEJ-P needle on the middle (4th) clip.

Thanks Gray! You guys are awesome :)

Am not. :banana:

:)

I'm searching for an air leak and I think I found one near the air boot from the filter to the carb. But I also noticed the exhaust gasket from the header to the midpipe is almost completely worn out. I can slip the midpipe off with the clamp tight. Would this also cause the idle to hang? Thanks in advance!

In most cases a "hanging" idle results from an intake boot leak between the carb and cyl. An intake leak on the air filter side, while not good will not exibit your issue as the fuel has not yet been atomized with air at this point in the flow. I've never experienced this issue with a dirt bike, but it's far more common on vintage street motorcycles. Spray some carb cleaner around the intake boot, and listen for an abrupt change in engine rpm's, if so, now you found your air leak.

In most cases a "hanging" idle results from an intake boot leak between the carb and cyl. An intake leak on the air filter side, while not good will not exibit your issue as the fuel has not yet been atomized with air at this point in the flow. I've never experienced this issue with a dirt bike, but it's far more common on vintage street motorcycles. Spray some carb cleaner around the intake boot, and listen for an abrupt change in engine rpm's, if so, now you found your air leak.

That's a good point. So it's most likely the boot on the cylinder, or one of the hot/cold start plungers???

ok i feel really dumb asking this but does anyone have a pic or number to refer to on the parts diagram of the vacuum release plate? i can't find it in my manual anywhere. :\

ah, ok... thank you. i was having a problem along these lines too but i think my problem was a small pilot. i went up a size but still putting my bike back together atm so i haven't been able to try it yet. my vacuum plate is in correctly so hopefully it was my pilot jet.

ah, ok... thank you. i was having a problem along these lines too but i think my problem was a small pilot. i went up a size but still putting my bike back together atm so i haven't been able to try it yet. my vacuum plate is in correctly so hopefully it was my pilot jet.

Let us know what happens. I've narrowed my issue down to a lean pilot too. It has a white bros r-4 pipe and stock jetting. I'm also getting a loud pop when trying to start it so I'm going to check the valve clearances and buy a new midpipe connection gasket.

*Just to clarify, I shouldn't be able to spin/remove the midpipe with the clamp tightened right?

ok i feel really dumb asking this but :\

Never a dumb question, but beware of dumb answers ! LOL :)

Experiencing a little bit of this myself, so following along.

Bump. :)

I had a bad hanging idle on my 426.  It did it worse as the bike got hotter to the point that it wouldn't even engine brake when I let off the gas - the idle just stayed high or climbed.  It got to the point that I would have to shut the bike off any time I came to a stop because it would idle so damn high. 

 

Here is what I did and it solved the issue completely.  The bike now comes back down to idle as if it were new.  Hope this helps anyone with the same issue.

 

1. Went up one size on the main and pilot jets (165 and 45, stock is 162 and 42) - I don't think the size increase is necessarily required, but I wanted to jet up anyway.  The key is to just get new and clean jets - especially the primary.  I think mine were the originals, 12 years old, and full of buildup from sitting with old gas.

 

2. Replace the gasket that goes around the slide plate.  Part#  4FN-14997-00-00  -  SEAL   My seal was rippled around the edges when I took it apart...Like the edges of a bacon strip.  The new on laid flat and tight.  Just be careful putting it on because it's delicate and make sure you have it facing the right way.  Compare it with the one that's on there.

 

She now purrs like a kitten now and starts second kick - hot or cold.  

2.    My seal was rippled around the edges when I took it apart...Like the edges of a bacon strip. 

 

Pilot jets can be cleaned, but that was probably your only problem.  The vacuum release plate seal normally looks like what you described after it's been used, but most of them will return to their proper shape once allowed to dry for 10-12 hours.  Then again, they're cheap, and a new one wouldn't hurt.

That's kind of what I figured, too.  But better just change everything for the little cost and time while I have the carb apart.

 

So get this...I finally get out on the trails this weekend and the bike is running mint and I was loving it after having this idle issue for so long...And then I stalled it in some tight single track and look down to see fuel pouring out of the bottom of the carb - a nice steady stream.  The drain screw had come out on it's own...FML.  Finally get it running right and my day is cut short because of a simple little screw....

 

If it's not one thing it's another!  But at least this time it's a simple fix.

 

PS.  Big thanks to everyone contributing on TT.  The database of info here is incredible

That screw is a special part, if I'm not mistaken.  It has a tapered point so that it seats against and closes the drain passage in the bowl.  Be sure you order it by part number.

You're correct.  I think it's unique to the 2001-2002 426.  

 

I originally thought any FCR drain bolt would do, but I was wrong.

 

Part # is:  3TJ-14191-40-00   DRAIN PLUG

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