Pulling out my hair, 2000 yz426f

So it had been a few years since it ran. I had done a 450 cam swap a few years ago, it was not running great but got stuffed in the garage while I recuperated from back surgery. 3 months ago I tore back into it. Rebuilt carb with moose kit. New oem valves, springs, timing chain, head needed one exhaust valve guide repaired by millennium, wiseco piston, cylinder swap from millennium as well. Adjusted valve clearance/shimmed up. 2003 450 exhaust cam 14 pins from intake cam. Good compression, new plug with appropriate gap, good spark. Turned on fuel petcock gas poured from overflow. Kicked until my foot was sore, backfired once but nothing. This morning turn on fuel, nothing pours from overflow, still won't start. Sweaty, sore,aggravated, losing patience and bleeding cash. Calling our favorite super hero gray racer to the rescue.

Hey man,

Not sure how much this helps, but a bike I was working on an a month ago ab that same year model but a 2 stroke started hemorrhaging gas through overflow after I rebuilt the carb, I tapped the carb bowl with the butt of a ratchet and it stopped (the float was stuck in the carb causing he gas to just kick right back out). Since you said it stopped the next morning I am assuming if it was the issue it fixed itself. A lot of times when you open the carb and you rebuild it or if the bike is older, condensation will cause the float to get a bit sticky, so I would check that if it does overflow again-sorry I can't help anymore man.

it has been a while but I thought it was 13 pins from the intake cam ?

Not when using a cam made for a 450 in a 426 or 400. 


The majority of starting troubles in these are carb problems, usually in the idle circuit.  Be sure that the pilot jet is completely cleared, and the passages leading up to the throat also.  You want to be sure your slide plate is on right side up, too.

I'm pretty tempted to just buy a 2005 or later 450 carb. wr or yz would work right?

I kicked mine for an hour until my foot was so sore I couldn't stand it. Changed the plug the next day and it fired on the first kick.

I'm pretty tempted to just buy a 2005 or later 450 carb. wr or yz would work right?


Avoid WR carbs.  They have unnecessary complications built into them because of the air injection systems on the later ones. 

What are the symptoms of installing the accelerator pump diaphragm up side down?(you can probably guess why I'm asking )

The diaphragm is built with a spring seat and a travel limiting "button" or "peg" on the bottom side.  I'm not sure it's even possible to install the spring on the wrong side, but if that were to be done, there would be no pump action at all.  If the diaphragm were installed upside down with the spring on the bottom where it belongs, the amount of travel could be affected either way.  Never run into it, so I can't say for certain.

Well after several kicks tonight and disassembly, soak in cleaner and reassembly the bike runs. However I have a new problem. As it ran it started to pour oil onto the ground from the top of the engine, the banjo bolt in the head was clean but oil was pooled around the banjo on the right clutch, crankcase cover. I quickly tried to tighten this and I over tightened it. The leaking one was the one obscured by the pipe, it was not fully run in. Don't know how I missed it but now a new problem. Do I just buy a new cover or JB weld the hole with the banjo in it. Seems too thin to drill, tap and helicoil.

Went with the helicoil, all is well, thank you guys

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