YZ450 not wanting to run without choke, please help.


7 replies to this topic
  • SquidHunter785

Posted July 31, 2016 - 04:50 PM

#1

Alright so I'm not a rookie, been around the sport for 25 years but I made a huge rookie mistake.

I have an '08 450 that had a leaky float bowl (from the seal between carb body and float bowl) on Friday and I wanted to ride yesterday so I did what anyone (or so i assumed) would do in such a predicament and put some Yamabond on it for a quick fix....but it wasn't Yamabond, it was RTV and i didn't notice until it was already way too late. So fast forward to yesterday and I go to prep the bike to head out and ride. I turned the fuel petcock on and it began profusely pouring from the float's overflow hose. I turned the gas off and tore the bike down to the carb so i could inspect it. As soon as I took the float off I saw the horror which was grey jelly blobs floating around the float bowl in the fuel. So i cleaned the float out, assembled the bike and fired it up. It ran great without any bogs or hesitation so I turned it off and put it away for the night. Today I went to ride, fired the bike up and it ran great, went out on the track and boom...half a lap in and the bike bogs and dies, sounds like it ran out of gas. I went to kick it and the compression felt low, low enough that i could crank the bike by hand. I pushed the bike over to the pits and threw it up on the stand, moved the kicker with my hand for a couple kicks and then the compression came back. I got on it and tried to start it...nothing. I pulled the choke out and it fired right up, idled great and ran great at low-mid RPM's until I gave it full throttle and it stayed at mid-RPM's and then fell on it's face BUT the choke was out so i figured it was normal. I pushed the choke in and the bike idled, as soon as i gave it gas it died. I took the carb apart, the jets were clear, the throttle moved fine, i saw fuel squirt into carb when i applied the throttle so that was all good. I put the carb back together and fired it up, did the same thing, wouldn't run without choke and popped upon decel so i knew it was lean which meant plugged jet or something. When i took the carb off the next time i noticed the o-ring at the tip of the Tusk air/fuel screw fell out and was in 2 pieces. I put it all back together and haven't touched it since.

So....it lost compression after stalling, the compression came back after a few kicks but the bike won't run without a choke. I'm going to clean the carb completely tomorrow and if I have to i'll check the timing. I have to order one of those o-rings too so hopefully that's the issue and we can stop it there.

Thanks for anyones help.


Edited by SquidHunter785, July 31, 2016 - 04:51 PM.


  • Krannie McKranface

Posted July 31, 2016 - 05:07 PM

#2

Ream the passage above the pilot jet with compressed air, fishing line, and mild solvent.

Any loose material gets clogged up there

 

Find the exit point of the passage inside the venturi, and blow backwards with the spray solvent (like brake cleaner)



  • SquidHunter785

Posted July 31, 2016 - 05:19 PM

#3

i should mention that after putting the silicone on i started the bike about 25 minutes later and let it run and heat up to operating temp, that's when i noticed the carb was pouring gas.



  • SquidHunter785

Posted July 31, 2016 - 05:21 PM

#4

also, what effect would that broken A/F thumbscrew o-ring have on the way the bike runs? and what would have caused the temporary loss of compression? I'm fairly new to four strokes.


Edited by SquidHunter785, July 31, 2016 - 05:24 PM.


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  • Krannie McKranface

Posted July 31, 2016 - 06:31 PM

#5

also, what effect would that broken A/F thumbscrew o-ring have on the way the bike runs? and what would have caused the temporary loss of compression? I'm fairly new to four strokes.

 

You can't have a partially working carb and expect it to perform well at all.

It all works together as a system.

 

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

 

 

Your compression issue is not related.

 

If you have not checked the valve clearances, or even better, inspected the valves for mushrooming, you really should.

Your motor is 8 years old.


Edited by KRANNIE, July 31, 2016 - 06:32 PM.


  • SquidHunter785

Posted July 31, 2016 - 06:58 PM

#6

You can't have a partially working carb and expect it to perform well at all.

It all works together as a system.

 

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

 

 

Your compression issue is not related.

 

If you have not checked the valve clearances, or even better, inspected the valves for mushrooming, you really should.

Your motor is 8 years old.


hey thanks for your help, i'll give the carb a good cleaning with Simple Green and then get in there with some air and carb cleaner. I'll give the give the valves a check too, i was gonna get in there to look at the timing just to make sure that wasn't the cause of the compression loss. 



  • Krannie McKranface

Posted July 31, 2016 - 07:33 PM

#7

hey thanks for your help, i'll give the carb a good cleaning with Simple Green and then get in there with some air and carb cleaner. I'll give the give the valves a check too, i was gonna get in there to look at the timing just to make sure that wasn't the cause of the compression loss. 

 

If you have never changed the timing chain, assuming you have typical hours of 30 per year, your are waaaaaay over due.



  • SquidHunter785

Posted July 31, 2016 - 08:01 PM

#8

i just got this bike, the bike has had 2 previous owners, the first didn't ride it because he fell behind on payments and his mom took it and stored it for 4 years while she paid the bank off, she then sold the bike to the guy i got it from. Supposedly it has about 40 hours on it, only aftermarket parts are an FMF Power Bomb with the FMF Ti-Powercore. 

How long should i let the carb soak in Simple Green?







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