00 YZ426. I'm at my wits end.

Hey guys I am new here. I picked up a 2000 YZ426 this week for a song and dance. I knew it needed a little work but I love doing this stuff. Anyways I get the bike home drained the fuel from the tank and carb and replaced. Tried to start it using the "start method" and it would fire for a second and that was it. So yesterday I did the valve adjustment and all are in spec. Timing dots are dead on, carb was pulled completely apart and cleaned, New plug ( tried 2 different new plugs). Now if you turn the idle all the way up and use the start method it will start for 5-10 seconds ( sounds rough ) but the second you touch the throttle it dies. I checked the acc. pump and it shoots a nice stream of gas when applied. This bike is completely stock with stock jetting. Any help much appreciated. You could save what little sanity I have left LOL.

How do you have the fuel screw set? It should be in the range of 1 1/4 - 2 1/4 turns out from seated.

Your problem sounds most like a carb issue, but it could possibly be ignition (like a faulty connection in the harness or internally within the coil).

Will it restart immediately when it dies?

Yes it will immediatly try to restart. I set the fuel screw at 1 3/4-turns out to begin and haven't messed with it since. It has a new stator and spark is strong every kick. When it does fire it almost sounds like a lawnmower, real rough and choppy.

A common mistake made by FCR first timers is the throttle slide spring plate. This is the plate on the back (engine) side of the slide. It can be installed upside down, and actually looks like it should go that way, but it doesn't. When properly oriented, the square side with the hole adjacent to the edge goes down, and the curved edge goes up. Check that.

I didn't pull the slide or plate. I will however check to see if the PO did install it backwards at some point.

Plate was installed correctly.

Did you play with the throttle position sensor at all; By "play with" I mean did you take it off the carb at any point?

Did you play with the throttle position sensor at all; By "play with" I mean did you take it off the carb at any point?
Good question.:thumbsup: If you had it off, unplug it and see if the bike runs better. If so, you will need to go through the adjustment process laid out in the manual.

Never removed the TPS, just unplugged it but don't know what the PO did before I bought it. We pull started it and it would run for a minute or so but ran like garbage and then would die. It started shooting water out of the weep hole so I checked my oil, you guessed it nice and milky. I just put new oil in yesterday. Engine is out due to the seals for the water pump being toast and upon pulling the oil filter, it's full of metal shavings. I yanked the engine and started to tear into it. It has a Moose clutch basket and the bolts coming through the back of the basket chewed the inner part of the basket. Guess I know where the shavings came from. The crank case and tranny look really clean from what I can see but who knows how much of the shavings went through both. All bearings are tight and clean and everything looks good so far.

I did notice however when pulling it apart that when the dimples on the crank were lined up and timed that the lobes were quite a ways different. The intake side was straight back and the exhaust side was tilted up and facing opposite of the intake which it's supposed to do as far as I know. Could the gear on the intake cam have slipped? We also noticed some compression coming back through the carb which tells me the intake timing is off but the dimples were lined up. Any thoughts?

Intake sprockets have been known to slip on the shaft, particularly when the shafts seize partially in the head.

Also, the water pump seals cannot contaminate the engine oil because any coolant that leaks by at the shaft escapes to the outside through a port under the pump designed for that purpose. Your coolant came from elsewhere.

The seals for the pump had been leaking for some time and the weep hole was mostly plugged. The water pump shaft was also worn with a groove. We layed the side cover flat and poured a little water where the impeller is and it all drained right through the seals and bearing. I am going to flush the cases real good and replace all the seals and gaskets and get a new set of cams. Guess doing the auto decompression will be sooner than I expected.

Welcome to TT and the 426 brotherhood! Good thing you picked it up cheap! You will love it once you get it going. Great bikes and reliable as a claw hammer if you do proper routing maintenance.

New question. Will both intake and exhaust cam from a 450 fit the 426? I don't really have the money for Hot Cams right now and with the 450 setup I will get the auto decompression and a new intake cam.

I don't know. I don't recall anyone ever asking before. Why do you want the 450 intake cam? I'm not sure the specs are really any different than the 426 cam...

Well it's my intake cam that's junk but I want to go to an auto decomp. exhaust cam. So if the 450 cams will fit, then I can buy a set off of Fleabay or something and I fix 2 problems in 1 shot. To do what I want I am going to have to buy 2 cams and that's the cheapest route I can find.

They will physically fir in the head, but the timing is going to be a problem, as will, possibly, the mismatch between the chain/tooth profile.

The 450 cam tooth profile is slightly different, and although this has never caused any trouble with those running the E cam in earlier engines, it was a concern early on. It might be significant if running both cams with this minor mismatch.

Also, the timing marks on the 450 cam are useless in an earlier head. Using the 450 E cam requires that the intake cam be timed on its mark, and then the exhaust is spotted off of that by counting chain pins between the top marks. With two 450 cams, you would have no reference at all, and would need to get the OEM timing specs from a cam grinder and use a degree wheel to set them up.

I don't recommend it.

Thanks Grey. That's what I needed to know. I will just find another 426 intake cam and a 450 exhaust cam.

Hey bud, I have the same bike, and when I first got it it did the same exact thing. Check, or have the compression tested. If low it definately wont run.


We couldn't really check compression due to the cam issue. The bike does however have a new piston and rings. Cross hatches in the cylinder are quite fresh and the piston has no visible wear on the skirt. Even with the timing being off it still had a good amount of compression. I am almost certain that this will be fixed by replacing the cams. But good idea and thanks for that.

Okay so I am going to buy a new set of Hot Cams. Seems to be the better way to go. Now why would the inner clutch hub rub the bolts from the basket? It is a Moose basket and in really great shape but the inner hub is toast.

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