Got the carb off. Now what?


5 replies to this topic
  • beairmo

Posted August 06, 2013 - 05:21 AM

#1

First, I have searched the forum and done a ton of research on this subject before posting. I didn't find specifically what I am looking for so thanks in advance for the advice.

 

My 2009 WR450F has the following setup

 

Year: 2009
Model (450):
Cam Timing (WR/YZ): Don't know
Main jet: 165
Piloticon1.png Jet: 48
PAJ: 105
Leak Jet: 55
Starter Jet: 72
Fuel screw (turns out): ?
Needle Model/Clip position: 5th clip up from the bottom
Grey Wire Mod (Y/N): Yes
TPS Connected (Y/N): Yes
Airbox Snorkel/Lid (on or off): OFF
AIS Removed (Y/N): Yes
Airfilter Brand: Twin Air
Exhausticon1.png Brand: FMF 4.1 with powerbomb header
Average Altitude: 800-1000'
Average Temperature: 60-90F
Average Humidity: 70-80

 

The symptoms I am trying to correct is the steady RPM stutter and backfire-popping on decel (real bad)

 

The bike starts good off button and idles fine. I had Yamaha dealer check exhaust with analyzer and they said it passes.

 

I have tried disconnecting the TPS and although it does make it run smoother, it still stutters pretty bad. Since I DS the bike I really need it to run smooth on pavement. I even replaced the TPS earlier this year and had no effect.

 

i have taken the bowl off and cleaned all the jets and every little hole I could find with carb cleaner. 

 

I checked the exhaust front to back, put in fresh gasket, and verified no leaks. Re-packed the muffler.

 

Before I put the carb back on, I would greatly appreciate any advice as to what I can do to make it run better.

 

Again, thanks in advance!!!

 

 

 



  • Thommo_400f

Posted August 08, 2013 - 02:55 AM

#2

2 issues:
Popping on decel is probably lean on pilot jet. Try a 50 or 52. Or initially wind out fuel screw a bit.

Stutter when cruising is usually slightly rich on the needle as it is only just lifting up when cruising.
I would try a leaner needle on the straight diameter with the clip down 1 or 2 notches. but maintain same taper etc. it allows you to lean it at low throttle without putting it too far down into the main jet hole.

  • Krannie McKranface

Posted August 08, 2013 - 12:19 PM

#3

Leaking/cracked hot start nut

Sticky hot start plunger

Leaking ACV cover.

Missing / worn oring on fuel screw

 

NEVER EVER USE CARB CLEANER ON A MC CARB

You will melt the internals!

 

Use only spray brake cleaner and compressed air.



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  • beairmo

Posted August 15, 2013 - 08:51 AM

#4

Leaking/cracked hot start nut

Sticky hot start plunger

Leaking ACV cover.

Missing / worn oring on fuel screw

 

NEVER EVER USE CARB CLEANER ON A MC CARB

You will melt the internals!

 

Use only spray brake cleaner and compressed air.

Thanks for the great suggestions. I really appreciate it. Looks like the fuel screw o-ring was missing. If it is stuck in the carb I can't see it or feel it with dental pick.

 

After researching and examining the carb over the last two weeks I have found a number of potential issues. missing spring on diaphragm. Needle valve was sticking. I ended up ordering all new gaskets and o-rings and anything rubber. Hopefully when I get it all back together it runs like the beast it wants to be! Great learning experience about carbs...



  • Krannie McKranface

Posted August 15, 2013 - 12:13 PM

#5

http://www.dirtrider...r_carb_rebuild/



  • stevethe

Posted August 15, 2013 - 02:01 PM

#6

If all else carb fixes don't fix the stutter try installing a dynatec ignition.




 
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