Cleaned my carb, replaced jets, still only run with choke on

11 replies to this topic
  • Nitrousman

Posted April 03, 2010 - 04:42 PM


Not sure what's wrong with this thing at this point. Occasional backfire while starting it, and it still only wants to idle with the choke on. I was able to ride it and once I got going it would run with the choke off but I had to keep the rpm's up or it would stall. pops quite a bit when coming off throttle while it's in gear. I blew out all the passages with compressed air and a full can of carb cleaner plus I replaced the jets. The choke button does not like to stay out now so I have to hold it with my hand while I start it. Are my valves screwed? This is the first 4 stroke bike I've owned and so far I really don't like it. The bike is in good shape but I can't figure out why it won't run right. It's a 2005 YZ 450F. I drained the tank when I had it off so it has fresh 93 octane gas in it now. Anything else it could be besides the valves? Thanks.

  • Nitrousman

Posted April 04, 2010 - 06:16 PM


Anyone have any suggestions?

  • grayracer513

Posted April 04, 2010 - 08:26 PM


Did you ever check your valve clearance?

  • Nitrousman

Posted April 05, 2010 - 05:47 AM


Did you ever check your valve clearance?

That was going to be my next thing to check. I've not done any work on a 4 stroke motor before so this will be my first shot at doing the valve check. Do the instructions in the FAQ cover my 05 YZ 450F? It doesn't show my bike in the list of covered bikes. Anything I should watch out for when I'm checking them? Thanks.

  • grayracer513

Posted April 05, 2010 - 07:46 AM


The procedure is the same, yes. The clearances for yours are listed in the manual as is the torque pattern for the cam saddle caps. While you're in there, check the cam timing before you take either cam out (if that becomes necessary).

If you just check them and find them OK, nothing further will be necessary, but if you have to adjust them, some important points are:

  • There is a half circle locator ring on top of each ball bearing. Don't drop it down the chain tunnel.
  • Reseat the caps BY HAND all the way against the head, using no more than a gentle tap or two with a screwdriver handle if necessary. DO NOT pull them down with the bolts if they resist. Figure out what the hold up is and fix it
  • Never remove the chain tensioner unless the engine is in the timing postion (TDC on compression) and never rotate the engine more than 30 degrees in either direction with the tensioner slacked off.
  • Don't turn the engine with either cam out unless you hold tension on the cam chain.
  • Use care in torquing the caps. Use a good torque wrench, don't guess. Take them up in three steps to their final torque specs, and follow the pattern in the manual. The book calls for 86 in/lb. IMO, that's more than needed, and I normally us 75 in/lb instead.

  • Nitrousman

Posted April 05, 2010 - 08:24 PM


Thanks for the info, dealer seems to think I have a carb issue from what I've told the tech so it might be worth a $100 bucks to have them look at it and rebuild the carb again. They think I have some varnish somewhere in the carb but everything seemed pretty clean to me.

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  • 426Dude

Posted April 06, 2010 - 09:38 AM


I had the same problem. I ended up cleaning it again and again but every time I would get the same result. With old street bikes the adage is you usually have to clean them three times. Anyway, I ended up sending it to ZipTy for their clean and mod. Works quite well now for $125. For the extra 25 it is probably worth it.
Good luck,

  • Icon

Posted April 06, 2010 - 10:43 AM


Did you have the slide out of your carb and if so did you reinstall correctly?

  • Nitrousman

Posted April 06, 2010 - 05:53 PM


Did you have the slide out of your carb and if so did you reinstall correctly?

No I didn't remove the slide but it ran like this before I even removed the carb.

  • Icon

Posted April 07, 2010 - 04:06 AM


You really need to check your valve clearance and your cam timing. If there are issues with either one of these, nothing you will do to the carb will make a difference.

  • Nitrousman

Posted April 07, 2010 - 07:41 PM


You really need to check your valve clearance and your cam timing. If there are issues with either one of these, nothing you will do to the carb will make a difference.

After I put the carb back together again if it doesn't run right I might just let the dealer figure out for $100 bucks. These are the times I miss a 2 stroke.

  • gscx

Posted April 07, 2010 - 08:04 PM


either bike will not run if you dont take care of it

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