2000 YZ426f not pulling fuel into cylinder?

15 replies to this topic
  • coda426

Posted October 19, 2012 - 09:38 AM


Help! I inherited a 2000 YZ426f which ran great when it was garaged in AZ 5 years ago. I'm trying to get it back up and running and have ran into a fuel issue. The bike is now in Colorado (Denver). I had the carb rebuilt and properly jetted proffesionally (they did it 4 times thinking this had to be the problem). The compression is good and I have spark (along with a new plug). The bike will not start! Nothing happens. It seems as if fuel is not being pulled into the cylinder. Any advice or suggestions would be appreciated. At this point I'l be doing the work myself.

Edited by coda426, October 19, 2012 - 09:40 AM.

  • William1

Posted October 19, 2012 - 10:04 AM


Is the plug wet after repeated attempts to start?
Did you do a leak down test?

  • coda426

Posted October 19, 2012 - 10:21 AM


No leak down test. Plug is not wet.

  • William1

Posted October 19, 2012 - 10:30 AM


If the bike 'feels' like you have some compression and does not run the plug should be wet, assuming the pilot jet and carb passage ways are actually clean.
If you open the drain screw on the bottom of the carb, does fuel come out? If not, either the petcock s clogged or the fuel inlet of the carb is clogged. Above the float needle seat is a screen.

  • coda426

Posted October 19, 2012 - 02:23 PM


Thanks for the help! I'll let you know what I find.

  • etuke

Posted October 19, 2012 - 03:30 PM


I tried for an hour to get my 426 started when I first bought it,I was soo pissed off I could have burned the bike.Guy who owned a 426 saw me kicking it over and decided he couldn't take it anymore and came to help.He had the bike going in 3 kicks,maybe its just your technique.Mine didn't offer once when I tried it the first time either,just a thought.

  • MNellis

Posted October 19, 2012 - 06:22 PM


I changed a piston on a 426 a while back and since I didn't touch the valve I just put the cams back in, timed them and went about my business. I spent days trying to get the motor started. I checked cam timing, ignition timing (sheard keyway possibility), plugs, wires etc. It felt like it had great compression but would never start. I did get it to pop once or twice but that was it.

I finally checked the valve clearances and found one of the valves to be very tight. I adjust the valve clearance and it fired on the 2nd kick. After sitting for so long you might have a sticking valve, or related, issue.

  • coda426

Posted October 19, 2012 - 09:26 PM


If I open the drain screw I get fuel out. I took the carb back off to inspect the jets and make sure everything is clear (it all looked good)(the carb has been off and cleaned now 5 times, 4 times by a shop and once by me). I kicked it over numerous times (around 40 kicks) and then removed the plug. The plug is bone dry. I do not have all the venting/drain hoses on the carb. Would that make a difference? Tomorrow I'm going to grab some starting fluid and see if I can just get it to fire. Any more suggestions would be much appreciated.

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  • coda426

Posted October 19, 2012 - 09:31 PM


I'm hoping it's not just my technique (not ruling that out). I've had numerous people try (some of whom have started these in the past) with the same results. I was thinking and wondering if valves could be an issue. I'll give that a try.

  • Dougie64

Posted October 20, 2012 - 02:30 AM


How old is the fuel? Anything more than a few months old and i'd be gettting new stuff.

  • etuke

Posted October 20, 2012 - 06:08 AM


does you kick start stop at the compression stroke or does it inch by?Mine will stop solid when the compression builds in the cylinder and I cant kick it any further unless I hit the decompression lever.If it inches by then you could have a tight valve.A tight intake will actually push the fuel back into the airbox if its leaking enough.

Edited by etuke, October 20, 2012 - 06:09 AM.

  • marv02

Posted October 20, 2012 - 10:44 AM


Just asking after you turn on the Gas at the gas tank have you tryed to open up the drain screw on the bottom of the Carb to make sure the gas has gas in it.

If there no gas in the Carb bowl check the needle seat and floats level see if the floats are installed up sie down if the floats are clipped into the needle corectly the though of the float should between the wire clip and the spring plunger not on top of the wire clip on the needle blow out the passageway from the fuel tbe inlet the the needle seat there could be crap in it not letting thre gas though.

If there gas in the carb pull the air box put your hand back of the carb Bell and kick the Bike over see if you getting a vacum if not there a problem most likley it in the head Vavles.

If you have a good vacum when kicked over it's in the carb somewhere.

After you get it running malke sure you put winter air the tires summer air dont work it the winter LOL good luck.

Edited by marv02, October 20, 2012 - 10:46 AM.

  • coda426

Posted October 20, 2012 - 11:41 AM


Thanks for all the advice! The fuel is new (about two weeks old). I think etuke is on to something (tight valve). It does "feel" like it has compression but I can kick through TDC. It definitely builds compression and gets much harder to kick unless you use the decomp lever but if you hold your foot on the kick start you can push past it. I've determined fuel is instantly getting into the bottom of the carb and I took another look at the jetting and floats and everything is clean and properly installed. I also checked for a vaccum and got a little suction from the cylinder (had the carb off at this point and checked directly at the side of the cylinder head). It did not feel like a lot of suction. I'm going to check out the valves next. I'm thinking the intake valve is the problem. I'm pretty comfortable with carbs (used to rebuild small gas engine carbs for a living (that was about 15 years ago!)) but not real sure about attempting the valve situation. Any good literature out there to help guide somebody through valve clearances and adjustments.

Thanks marv02...I actually just put fall air in tires to be safe LOL!

  • marv02

Posted October 21, 2012 - 11:20 AM


Look around I dont remeber where but some where on this site there was a link for the factor manual tells you how to adjust the valves thats where I gotten mine.

Or PM me with your Home E-mail and I try to help you out.

  • jbrooks26

Posted October 21, 2012 - 01:06 PM


You will also want to make sure you aren't chasing a ghost here with the compression. Many of the 400's and 426's have had updated cams installed to achieve an automatic decompression. The only way to tell if you don't know is to pull the valve cover and look at the exhaust cam. If it's auto decompression, you will see a small lever looking piece in the center of the gear side and a pin over one of the exhaust valves. I have an 02 WR426 and mine can be hard to start when even slightly cool outside, I have to turn the idle up about 1.5 turns sometimes if its real cold, and then adjust it back down when it comes up to temperature. Also, don't overlook the starter jet, if it's clogged, your choke isn't doing you any good. The starter can only be accessed with the bowl removed from the carb. Hopefully this helps.


  • marv02

Posted October 21, 2012 - 01:37 PM


My 426 has the Hot cams it still has compression and I still have the decomprssion lever also.

I kick my bike though 5 times before I run the bike when it's cold to clear it out and get some oil up into the motor before I start it up.

Normaly then it starts on the 1st or 2nd kick every time.

Edited by marv02, October 21, 2012 - 01:38 PM.

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