wr426 starting / timing issue

I have attached 3 images (cams, flywheel, air boot).



This bike has been modified before I bought it. Exhaust cam was set forward 1 pin.

A blue wire is severed also. It ran, but owner always had it warmed up before I got to his house.

I haven't been.able to start it. I also reset the timing.

( chains have slipped since, so there is no way to get back to original teeth.). It backfires when we try using starting fluid in the air box. The boot also gets hot while trying to kick start. IMG_20130603_181143.jpg

I've moved both teeth forward 1 pin from shown location with no better luck...

Any ideas?

Moved the intake can right 1 pin. Still backfires...

Timing looks OK in picture.

Backfiring = Too much fuel

What is your starting proceedure ?.....

NEVER EVER turn the throttle when kicking. FCR carb will flood cylinder and cause a big backfire.

ALWAYS kick from just past TDC in compression stroke with one hard kick. Any other method will just stuff your ankle or the kickstart shaft (unless it has Auto Decomp cam).

If jetting is correct it should start in 3 kicks max. (with Choke when cold)

You need to confirm your carb jetting to be sure. Otherwise you will just go in circles.

The manual will tell you the stock Pilot, Float and Needle settings. Start there. Also make sure your idle screw isn't turned up too far (which often masks jetting issues)

post back if you need help

Thanks. I'll reset the timing to how it looks in the image and try the Carb.

Also, it may help to mention the backfire comes from the air box. Not the exhaust.

If you have time and want to cover all options. Post full jetting specs here as there are always a few jetting guru's lurking.

With a CLEAN carb....

Here is a starting point

Pilot jet (42)

Pilot Air Jet (75)

Fuel screw (1.5 turns out from bottom)

Main Jet (165)

Main Air Jet (200)

Needle model and clip position (OBDRR #4)

Stock as far as I know. I only changed timing because he said he had it changed.

Was pretty tired when explaining.my trouble. Let me try to be.more.detailed.

Only.time it backfired is when.I.use a starting.fluid.

It.backfires through the air box.

Cams are set as shown in photo.

Jets are stock as far as I know.

Carb is clean and clear. Just checked.

New spark plug.

Starting procedure....

Turn.on key

Open fuel

Open choke (cold)

Set kick to compression stroke


Feel disappointed

Go to step four and repeat

Exhaust valves seem to open somewhere around 3 to 4 pins after tdc. Can someone show a picture of what the cam lobes look like at tdc when correct?

Edited by s3v3red

Seems the diaphragm (12) is warped? Could this be the cause?


Ummm. Should this hole be here? (Top of the float bowl)

That looks very suspect...I don't have a 426 carb but the hole looks home made!

Does it go right through to outside?

no, not sure it goes anywhere, but it looks as though its been corroded away...

I'm not much more hlp unfortunately.

I would remove the Pilot, Main, PAJ, MAJ, Starter Jet and soak them in Carb Cleaner.

Set needle to #3 clip

Remove fuel screw and check O-Ring, then reset to 1+1/2 turns from bottom.

Make sure slide plate valve isn't upside-down (often stuffed up and causes all sorts of strange results).

Make sure Idle screw is only lifting slide by a couple of mm.

Re-assemble and try again.

I found a pic of the upper bowl, using google, and that hole does not belong there.

The clip is currently set to #4. Which way is #3? Down 1 or up 1? That lowers or raises the needle?

Thanks for all the help... hope I'm not out of a bike. I just bought this thing.

Clip #3 or #4 should be fine, only effects low-mid throttle, not starting. BTW Clips are counted from top.

You could try tow starting it and then see if it starts after that. My WR400 did it once. Had to tow it on tarmac to get it going and then never had a problem after.

Starter fluid is just hiding some other problem.

I have a carb apart today and mine has same hole, bike has been sitting so cleaning it now will let you if it runs ok

I found a pic of the upper bowl, using google, and that hole does not belong there.

Oh yes it does and should look just like you described it but it is not from corrosion...


The timing seems perfect in your pic. Maybe you are 180* out. Remove cams, turn crankshaft counterclockwise one revelution until the ''I'' mark on the rotor is aligned with stationary pointer. Now refit the cams as pictured in your pic.

Can't hurt to try.

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