yz450f starting problems...please help!

i have an '06 yz450f, it takes a million kicks to start it and when i do get it to start(rarely) it runs very hot, backfires alot, and stalls. I get good spark and have fresh fuel....what else may it be? Please help as i dont have the money to pay a dealer to fix it and just wanna ride. I have a service manual and nothing seems to add up.

-Thanks in advance

check your fuel screw, count how many turns out it is. thats where i would start.

I had the same problem with my 450. Kicked it so much a cracked the kick starter arm (which cost $160 to replace). I sent my carb to: http://www.tokyomods.com/ and now it starts on one or two kicks, idles nice and no popping! I think they charged me $175 and you can mail it to them and they mail it back modified with the proper jetting for your elevation. Best $175 I ever spent.......

how do i check how many turns out the fuel screw is?

do you know what sizes jets they put in yours?

Turn it in all the way and count how many turns it takes to get there. Just run it in till it stops, not to tight or you will damage the tip. A good carb cleaning probly wouldnt hurt too, if the bike sat for any length of time. I cleaned mine 3 times before it started easy and ran right. It sounds like the pilot circuit is clogged. Make sure when you cean it, pull the jets and clean out all the little passages in the carb.

Edited by nor-calYZ426
how do i check how many turns out the fuel screw is?
do you know what sizes jets they put in yours?





Your '06 should probably be jetted with a 45 pilot and a 168 main as starting point. Your idle speed may need to be raised to help it start better, too.

When staring an '06 cold, be sure you have pulled the "choke" (black knob, left side of carb) out, and that you twist the throttle from closed to half 2-3 times to get a prime from the accelerator pump. If it doesn't start in two kicks with the throttle CLOSED, give it a couple more twists. If it doesn't start on the next one with the throttle closed, crack the throttle open JUST barely above idle and hold it there for the next kick.

Hot starting is different; never twist the throttle first.

alright ill try taking the carb apart and cleaning it out and after i do that ill try starting it the way grayracer513 said to. thanks guys....ill get back and let you know if its better or not asap

With regard to cleaning the carb, avoid dipping/soaking where possible. Dips won't harm the bearings but they aren't good for the main body/bowl joint gasket. This is the joint held together by 4 screws that are visible once the float bowl is removed that hold the upper float chamber casting to the main body of the carb. The gasket in that joint IS NOT SERVICED (you can't buy it anywhere), so DO NOT REMOVE those screws.

Dipping is also not beneficial to the TPS. You could remove the TPS for cleaning, but readjusting it on an '06 is a huge PITA, so don't unless you have to.



how do i go about taking off the carb the easiest way...ive done it before but its a bitch and how do i remove the hot start cable?

The hot start cable unscrews from the top of the carb by means of the 12mm plastic nut at the carb. Be careful with the nut, it's quite fragile as far as the threads go.

  1. The easiest way to remove and reinstall the carb is to do it my way:
  2. Remove the seat, side number plates and muffler.
  3. Remove the 4 bolts holding the air box to the sub frame, leaving the air box clamped to the carb.
  4. Remove the 3 bolts holding the sub frame and slide the sub straight back off of the air box.
  5. Remove the air boot from the carb, unbolt the top of the shock, and remove the carb.

To reassemble, install the carb, install the shock, clamp the air box to it, slide in the sub frame, and put the bike back together. Trying to get the air boot in place around the shock while it's bolted to the sub frame is just too big a PITA.

okay guys...sorry its been a while i havent had the time to work on the bike, but heres a few more things that may lead you too more ideas that could help me. When i first got the bike it started and ran but took about 15 or 20 kicks and ran hot, stalled once it got too hot and backfired alot. So by what i was told i checked the valve clearances and found there were 3 off so i replaced them with the correct sizes and now it wont even start. As far as the timing goes, you line up the dots on the camshafts at 9 o'clock and 12 o'clock for exhaust and 12 o'clock and 3 o'clock for intake and line up the mark on the hole at the bottom end seen through the plug hole. Is there anything wrong w anything ive done, is there anymore to timing it (timing light maybe).

Double check your valve clearances again. Make sure you are at TDCC. Look at the cam lobes also and make sure they are pointing away from the valves. If you got to big of shim in there, the valves are gonna stay open. If you have a manual it will show you step by step how to do it. As far as the hard to start, running hot and backfiring, I'm gonna stick with carb issue. My yz426 did the same exact thing when i got it. I cleaned the carb twice and it still ran the same so I to thought it must be the valves. Checked them, were all in spec. Cleaned carb the third time and the bike runs great.

haha...yea theyre a bitch. Ill try that tom, im just really hesitant about pulling the carb apart cuz it looks like a million piece jigsaw puzzle

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