New yz426

Just picked up an 02 yz426f last week. It was sitting for 2 years so got it at a steal. Cleaned the carb up and learned how to start it (lol) but it pops a lot so I haven't riden it really. Prob take it to the shop and have it fully serviced and put the new tires on since I'm new to these bikes. A new seat cover and maybe some other dress up stuff, it will look nice.




Save yourself a trip to the shop ... the 426 will pop and run great at the same time.


Meet some Thumpertalk folks and have then hear the bike 1st.

Really?? It sounds pretty nasty. I have one friend who heard it and the first thing He said was dont ride it till the valves are adjusted. And another who says just ride it. Adjusting the valves myself sounds easy enough If I have to. Pretty excited to take her out tho being the first big 4 stroke I've ever had. I'll put a video up of it. And a question, I heard it's not good to let it sit and idle, whats the best way to warm it up?? How long?

Pops on decel, or when you are reving it up? Change the plug, did you check the jetting? Mine needed jetting it kept fouling the plug and it popped alot on excel and decel, they all pop on decel but that can be reduced with good jetting.

Deceleration, I didn't check the plug though. I cleaned the Jets and then started adjusting the fuel screw

Congrats!  I just picked up my first yz426 today.  Super stoked to get out and ride this weekend, just hope I can figure out starting it by then :|

I checked visually for leaks and nothing, I'll do the carb spray test today though. And I put a new adjustable fuel screw and it seems to be a little better. It starts always on first kick. But ya me too! I'm hopiing to ride soon. Starating is easy once you get it down. When the compression gets its hardest pull the decompression lever and just barely move the kickstarter, then release the lever, bring the kickstarter back up and kick.

Runs a lot better but still a couple pops on deceleration. And is it normal for the Vin numbers not to match on the neck and motor?



The engine numbers never match anything. 


But, that frame is a 2000 model, not an '02.

Ohhhhhhh. I was told it was an 02 when I bought it. My fault I guess. I noticed the y last night making it a 00. And is there a big difference on the 00 than the 02?

Not big, but there are a couple of things.

I searched on here and couldn't find anything on this but I'm cleaning the carb and I'm wondering if I should take off the bottom part of the carb? Is there any reason why I shouldn't?? Or is it necessary for me to?


No, you shouldn't remove it.


That's less an absolute than it first looks like.  You can, but there's a problem.  The problem is that Yamaha nor Keihin either one service the formed "O-ring" gasket that seals the two halves, and there is only one source for replacements, as far as I know; JD Jetting.


Not so much in the newer carbs, but every now and then on the older FCR used on the 400/426, it is actually necessary to separate the upper body from the lower because a passage is clogged with old varnish.  But if you think you need to do that, you should wait until you have the new gasket in hand before you take it apart at that joint.

Thank you, I had started on one screw before I posted, good thing I did. And I've been cleaning varnish out of.the passages, especially where the fuel first enters the carb, there's a lot of green no wonder it popped like that . I'll just clean it a few more times. Thank you!!

Another question. The valves were checked before I got it I guess. But I replaced the pilot jet (160 main 45 pilot) and no air leaks but still the popping on deceleration when I ride it somewhat hard. It runs great, idles and starts on first kick hot or cold. But the question, will changing to a 48 pilot maybe stop the popping? I was gonna try it Tuesday but just wondering in the meantime. It also bogs now if I twist the throttle fast now, it didn't before changing to new 45pj.

I picked upa 2002 YZ426F about 3 wks ago. I did soe researchbefore I got it,said they're hard to start(stubburn). So I ordered the jet kit from JD Jetting,and got te Hot Cams Exhaust cam w/ auto-decomp. Was said (in my research) that those 2 upgrades should make this bike start a lot easier. Have any of you done this,and does it mae it easier? I get the bike back tomorrow from teshop installing the parts. Thx

The 426 is not that difficult to crank up in stock trim IF you follow procedure correctly, and keep the carb tuned.

The cam does simplify things by relieving the rider of having to locate the "sweet spot", but proper tuning and technique still matter some.

I don't use or recommend anyone's jet kits. Most are too expensive, and include things you don't need. I'd much rather make whatever specific adjustments are required using Kiehin parts.

I got the 426 back rom the shop today. They installed the new Hot Cams Exhaust cam, JD Jetting jet kit. It starts nice n easy.I put all new engine ice in it,oil and filter change. It's ready too tear some stuff up.I should be taking it, and my 300exc to a hare scramble and an endure this wknd. See how it does.

I have a 2000 yz426 (stock) and it starts first kick every time and if I dump the bike max 5 kicks with hot start.

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