2000 yz426f issues

[cole40]

Hey guys, I just got a 2000 yz426f yesterday. I am having a hard time starting it, it has been sitting for a while. I changed the spark plug and took the gas tank off and emptied it and put fresh gas in it. I noticed when I turned the petcock on it started leaking fuel out of the bottom of the carb bowl. I went ahead and ordered a new petcock because the current one is pretty rough. I guess my questions are: 

1. What is the best way to start this monster? (I read a lot about how hard this bike is to start)

2. Why is fuel leaking from the carb bowl?

3. Can someone explain the hot start function? 

 

Thanks guys!

[Pegleghero]

I remember my old 426 leaked fuel like you said, the float ended up being stuck and tapping the carb with the back of a screw driver ended up freeing it up. I know it wasnt the right thing to do but I was out on the trail and didnt have much to work with. Either way it stopped the leak and I never had the problem again. And as for starting mine was the same. Luckily, I have a nice hill next to my house so I'd always end up just bump starting it down the hill. After it popped off a few times I could kick it no problem after that. Thats until the next time I let it sit lol. And as for the hot start I never used it, just the de comp lever.

Edited December 16, 2013 by npverhey1

[cole40]

Thanks man, I might as well pull the carb and do a check and clean. How does the comp lever work? And whats its purpose?

[Pegleghero]

In simple terms it allows you to kick the piston through the stroke. Hopefully one of the more knowledgeable guys will chime in and give you a better answer than I can lol. But I know for me to start my 426, I had to push the piston to TDC and then pull the comp lever just enough to get the piston past TDC and then kick it like you have a pair. If it didnt start, I just repeated the process until it fired up.

[cole40]

Alright cool, thats what I saw on a video of how to do it too. Im gonna clean the carb first then ill give it a try again. Thanks man!

[grayracer513]

The correct starting technique is shown here:

 

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_a.mpg

 

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_b.mpg

 

The function of the compression release is to release compression while setting up to start by allowing you to advance the engine through the first part of the compression stroke without resistance.  It does this by raising the right hand exhaust valve off its seat slightly.

 

The hot start plunger opens an air passage from the intake bell in front of the carb slide to the intake tract on the engine side, basically creating an air leak of a controlled size.  When the engine is very warm, as when it was stalled while running, it is exceptionally prone to refusing to start for reason of being too rich.  The hot start helps with that.  It's not usually needed in cases where the engine has just a minute or two to cool down.

 

Fuel leaking from the carb is usually a problem with the float/level controls.  Either the float is physically stuck (or assembled upside down), there is dirt between the needle and its seat, the needle tip is worn or damaged, or, in your carb, the O-ring that seals the needle seat to the carb body is leaking. 

 

When working on the carb, DO NOT remove the four screws inside the top of the float chamber holding the upper and lower body halves together.  No gasket is available for it.  Also, do not remove the throttle position sensor unless you want to have a whole bunch of fun trying to recalibrate it.

[NitrousR1]

The correct starting technique is shown here:

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_a.mpg

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_b.mpg

The function of the compression release is to release compression while setting up to start by allowing you to advance the engine through the first part of the compression stroke without resistance. It does this by raising the right hand exhaust valve off its seat slightly.

The hot start plunger opens an air passage from the intake bell in front of the carb slide to the intake tract on the engine side, basically creating an air leak of a controlled size. When the engine is very warm, as when it was stalled while running, it is exceptionally prone to refusing to start for reason of being too rich. The hot start helps with that. It's not usually needed in cases where the engine has just a minute or two to cool down.

Fuel leaking from the carb is usually a problem with the float/level controls. Either the float is physically stuck (or assembled upside down), there is dirt between the needle and its seat, the needle tip is worn or damaged, or, in your carb, the O-ring that seals the needle seat to the carb body is leaking.

When working on the carb, DO NOT remove the four screws inside the top of the float chamber holding the upper and lower body halves together. No gasket is available for it. Also, do not remove the throttle position sensor unless you want to have a whole bunch of fun trying to recalibrate it.

I don't recommend removing the 4 tamper proof Torx screws for the FCR mid body either but they do make a replacement gasket if you absolutely have to. I had to take the mid body off one to free a clog in the accelerator pump circuit.

JD Jetting sells the genuine Keihin gasket. For your cleaning you shouldn't need to

[grayracer513]

I don't recommend removing the 4 tamper proof Torx screws for the FCR mid body either but they do make a replacement gasket if you absolutely have to. I had to take the mid body off one to free a clog in the accelerator pump circuit.

JD Jetting sells the genuine Keihin gasket. For your cleaning you shouldn't need to

 

Do they have one for the FCR and the newer FCR-MX, or only the newer one?  I'm assuming they differ.

[suzuki son of a bitch]

Not to be a dick but those bikes are ticking timebombs from what i heard. You should have gotten a yz450f. The 400 and 426 are stepping stones to the 450

[NitrousR1]

Jd says he has them both for both the FCR and FCR-mx. The one I did was just a FCR, not the mx Version.

It had a very tiny spec of dirt clogging the acc. Pump right where the gasket goes. No amount of carb clean and compressed air would get it out. Separated both case halves of the carb and it came right out. I'd imagine that's pretty rare though, but good to know they can be bought just in case.

[NitrousR1]

Not to be a dick but those bikes are ticking timebombs from what i heard. You should have gotten a yz450f. The 400 and 426 are stepping stones to the 450

They are decent bikes. I'd prefer the 450 myself but had 400's and 426's before 2003 and they were reliable then.

Most people's problems with them come from previous owners never taking care of them. no preventative maintenance with valves pistons and timing chains. They just ride them Til they blow. Properly taken care of and maintained they should be as reliable as a 450.

Putting in a auto decomp exhaust cam makes the starting drill alot easier for a new owner.

[essex426]

I still have an 02 426 with the 450 cam mod and jd jet kit, that i have owned for eight years, starts in 2 or 3 kicks every time, even if it has been left for months.

So dont see them as timebombs at all.

Just a case of looking after the engine.

[cole40]

Thanks for all the great info guys, keep it coming. My carburetor is clean and adjusted correctly and the leaking issue is fixed now. I had to readjust the float. My new petcock works great and its running great. I am still learning a few techniques to starting this thing. This particular bike was very well taken care of and will continue to be. It was at one point owned and ridden by Ty Davis(have a signed form). This bike has a great amount of power. I still cant believe how responsive this bike is, I usually ride a raptor 660 and on road bikes such as a zx11 and a r6. This bike is a whole different kind of monster. 

[mike_dean]

No not time bombs at all, my 2000 426 has over 500 hrs, original valves (stainless steel), one piston it really didn't need, 2 timing chains, keyway, Hinson clutch basket.

 

[Pooley]

Not to be a dick but those bikes are ticking timebombs from what i heard. You should have gotten a yz450f. The 400 and 426 are stepping stones to the 450

You've heard wrong.  I've a WR with over 15k miles of singletrack.  Have yet to adjust the valves and have only replaced stuff like cam chain and valve guide seals...the normal wear and tear items.  Treat them right and they will treat you right.

[cole40]

Hey guys, as I stated earlier I bought a new petcock from the local motorsports place. The problem with the old one was that it would leak gas whether the switch was on or off, and also it would leak and drip from the petcock to the floor. I replaced the petcock and gasket and it functions properly but Im still having the external leak. Is this a common thing? I need to add that I have one of the larger enduro tanks on this bike. 

[grayracer513]

A lot of the aftermarket tanks don't have a flat enough bottom around the petcock to seal correctly using the OEM formed O-ring seal that comes with the petcock.  They normally ship with their own additional gasket.  I've made replacements from pieces of 2mm thick fuel/oil proof "rubber" gasket stock from an auto parts house.

[cole40]

Thanks grayracer, thats on the lines of what I was thinking. The old petcock had one with it that looked aftermarket but its pretty old and cracked so Im gonna get a new one. While I am thinking about it, how long is the regular life of a CR8E spark plug on this bike? Considering at the moment this bike is not being raced, just trail riding.

[grayracer513]

To gauge the condition of a conventional spark plug, look at the tip of the center electrode.  If it appears rounded significantly, rather than a nice square cut, it IS (not might be) interfering with the efficiency of your ignition.  The sharper the edge is, the easier it is for a spark to jump from it and cross the gap.  Because the 426 has a weaker coil output at cranking speeds than does a 450, this is a bigger issue on the older bikes, and will mostly affect starting ability.

 

I run NGK iridiums, and they last me over a year.  I replace them more or less annually.  I would guess a conventional in a 426 would be good for about half that.

[cole40]

Awesome thanks for your help.