Dave and Bill gave excellent advise. I have the same bike as yours and when I bought it used and it leaked gas with the fuel on. Thus, I took it home and decided to clean it up since it had been riden in the sand alot. I decided to completely clean out the carb and did what everyone recommended. Unfortunately the 2001 bikes did not get the rubber boot to cover the side plastic cover where the cables enter the carb like yamaha later did in 2002 and it was filthy with old gas, sand and other grime. I only noticed this because my son's '02 has it and his carb was nice and clean. (NOTE: FOR THOSE WHO EVER WONDERED! After talking to YAMAHA engineers, they appologize that the schematics for even the '02 426 does not show this boot, but did pull an '02 cable assy off the shelf and verified that it comes with the new OEM throttle cable.)
Anyway, FIRST get your manual open to the carb section. You need to remove the side plastic cover, which has to be removed anyway to remove the cables, to clean the actuator and pump rod areas. Second, with the carb out, remove only the four bottom carb fuel bowl screws to clean the bowl and passages and check the valve seat and float level. Float level check is given in the manual as well as the valve and valve seat that is retained by the one phillips head screw within the bowl. I didn't have to adjust my float at all, but you should check yours to see if the shop messed around with it. (My fuel leak was from the worn o-ring on the valve seat, which I found out as it just fell out when I removed the screw. I replaced it with a new o-ring from the hardware store and it hasn't leaked yet.) Third, carefully remove the three small screws to your carb pump cover located on the bottom of the fuel bowl already removed. Be sure to carefully remove the rubber pump diaphram. I found tons of junk build up here and in the small pump fuel holes from where the dirt gets past the plastic cable cover and down thru the pump plunger rod hole. Whatever, you do, just make sure that all rubber is removed before blowing out the passages with carb and choke cleaner.
Once all is clean, you can put it all back together but leave the side cover off. To check if the slide cover is upside down, you have to remove the two screws on the top carb cover and remove it's phillips screw to the slides actuating rod mechanism inside. It's pretty easy, just make sure you note it's turns for the spring tension to it for reassembly. Carefully slide it out to verify the cover with the picture of it in the manual. If the V end is down, the shop screwed you over. Be sure to add some grease to the rods needle bearings if they look dry upon reassembly.
After I cleaned my carb and tried to start it, I had the same problem for two reasons. My dumb butt put that slide cover upside down and I removed the fuel screw on the carb bowl for cleaning without counting the factory set turns. I'm sure the shop messed with this to set your closed to 1/4 throttle setting. (I highly recommend an aftermarket fuel screw that you can turn by finger unless you have a fuel screw tool. I got mine for $10, TUSK brand, from rockymountainmc.com)
With a clean carb, correct float level, properly installed slide cover, and properly adjusted cables as also listed in the manual, I started my bike with the fuel screw 1 &1/2 turns out from all the way turned in. With the bike cold at TDC, fuel on for about 20 seconds to fill the bowl back up, and three quick primes of the throttle, my bike fired right up. However, I had turned the idle screw to far up to compensate for the lack of turns out at the fuel screw and it raced like crazy with the choke out and I noticed my header pipe start to glow red. I shut it down immediately and then turned my fuel screw out a 1/4 turn at a time with the same process above and eventually found my setting to be best at 2 & 1/2 turns out. This allowed me to set the idle screw lower each time to get rid of the glowing red header. Once I found the right setting for the fuel mixture screw and idle, my bike has never had a problem starting on the first kick since. I do periodically remove the side plastic throttle cable cover from the carb to check for dirt after a few rides now and you don't have to remove the carb to do this if you remove the coil first.
Hope this helps. Please post any questions on this that you may have. I know I wanted to shoot my bike after a weeks worth of disgust, but the friends here at ATM saved it from death.
Brian
Semper Fi!
Quote:
Originally Posted by bgdaddyn  I have a 2001 yz426. I bought the bike new in 2002. After about a year of riding, I started having problems with the carb. The bike has been in and out of the shop since then. Everytime I take it in, it cost me about $400 to rebuild carb. When I first got the bike, you could not touch the throttle or it would not crank. Now you have to twist the throttle 10-12 times with choke on and it will fire and then cut back off. Eventually it will crank and stay cranked, but it takes forever. The last time I took it in to the shop, they replaced something in the carb that recycles the gas and it worked for about a month and then it was back to what it was doing before. I haven't been able to ride much because the bike stays in the shop. The carb has been rebuilt 4 times over the years. If anyone could offer some suggestions or solutions, I would appreciate it. |
01-08-2007, 03:51 PM
2001 yz426 carb problem (need help) 
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Go to [Only registered and activated users can see links. ] and you can download the entire 01 426 manual in zip files... just click on the tech articles link. 
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