My first project bike WR426f

I am not a mechanic. I'm an electronic engineer and Network Engineer. But I dabble in lots of stuff, and I've been looking for a hobby I actually enjoy for a long time. After a trip to DurhamTown in GA, I wanted to get a few dirt bikes for the family, but they are so pricy!

So I did what any technically inclined person might do: I bought a non-running bike for cheap that needs a bit of restoration.

I did my research: as long as it has compression, it should run. So I found this non running wr426f for $900 with a new top end, few new misc parts, bought a hitch carrier for $160, and picked up the beast.

Now, before I can even begin to work on the engine, the fairings, seat, tank, rear subframe and air box had to come off. Not too hard... I followed others recommendation to wash the bike first - it's a good one - even after the pressure wash, it was still messy to handle.

But here it is, ready to dig into the engine!

First three things wrong:

1. The clutch would not disengage the transmission. Simple fix. Turned out the oil had set so long it gummed up and the plates were seized. A bath in degreaser fixed that.

2. Figured the carb would be the main issue, so bought a rebuild kit. Well in doing some research, there are 2 issues with these carbs. 1) the slide develops a gap causing air leaks. 2) there is a fuel pump that doesn't work real good due to weak spring, causing bottom end bog when hitting the throttle. But neither of these prevent starting, and it turned out the carb was clean. The only thing it really needed was the gaskets for the fuel inlet.

3. Oil change. After fixing the clutch, it needed new oil anyway. but don't forget to clean the chassis oil screen on these bikes in addition to changing the oil filter!

Well, still not running, so now what? Well, if it don't run, it's either:
a. Spark
b. Air
c. Fuel
d. Compression

a. I checked spark and replaced the plug. all good there.
b. I have the breather off, so it's not an air issue.
c. I know it's got fuel now, even sprayed starting fluid, got a little hit once, but that was all.
d. Compression is strong, so much so I almost cannot kick past TDC without the decompression lever.

Now what? After doing some research, I found 2 more things to check, related to compression and spark due to these bikes being notoriously hard to start.
1. Valve clearances
2. Timing

So I bought a feeler gauge and pulled off the valve cover and set the engine to TDC.

All valves were at or below minimum spec, which is not good. This bike uses "bucket and shim" style valves lifters, so you want closer to max spec, as I learned clearances shrink with time. But again, this shouldn't keep it from starting, though it could make it harder to start.

Finally, I tool a closer look at the CAMs. The alignment markings looked odd when I put the engine at TDC to check the valves, but I wasn't familiar with how timing worked at first so I didn't pay it much mind. Looking closer, I found the exhaust cam is off by 1 tooth! That could make it even harder to start!

So what to do?

First, I don't want to fight this bike every time I want to start it, so I ordered the HotCams exhaust cam with auto decompression. Everyone says it makes the bike much easier to start.

Second, I have 4 bikes now that take 9.48mm OD valve shims, so I ordered the big AHL shim kit from Amazon for $90. Unfortunately it is coming from China and they shipped USPS, so they won't arrive until middle of Jan... Oh well, I have another project bike to work on until then.

I'll post again once I get the shims and the new Cam is in this beast with properly adjusted valves and timing.

Parts:
$146 Hot Cams Stage 1 Exhaust Camshaft #4035-1E Yamaha YZ426F/WR400F/YZ400F/WR426F
$37 Moose Carburetor Rebuild Kit Yamaha YZ426F 2000-2002
$90 AHL Adjustable Valve Shim Kit 9.48mm O.D. for Yamaha YZ426F YZ426 F 2000-2002 (208pcs)