Wr/yz 450 won't start

2 replies to this topic
  • hate mcdead

Posted January 08, 2012 - 07:48 PM


I have a WR that is converted to a road racer. Will run Pikes Peak this summer as well as numerous road races this year. Here's the specs:
2008 WR450
J&E 12.75 Piston
Dyna programmable ignition
STM slipper clutch
Kibblewhite ti valves & springs
Ported Head by Orient Express
R6 front suspension with Ohlins 25mm cartridges
Ohlins custom rear shock
YZ close ratio transmission
Oversize rads
Excell spoked wheels, 2 sets, 1 set for rain tires
Brembo master cylinder
Woods rear sets.
Ferris Ion battery
Full body work

Dyno: 59 rear wheel HP
Carb untouched/stock except for some main and needle work on the dyno.

The bike has gotten super hard to start. The electric start works great but the bike just won't quite get running. Leakdown test at only 8%. Adjusted valves, changed coil, changed plug. No difference. I'm pretty sure the engine and ignition are fine so this leaves the carb. I use starter rollers to get it going and once it is running its awesome. But need to get back to where it just fired right up off the starter motor.

I'd like to get the carb tuned to the max since its stock. I would like so help on who to send it to or what to change out.

Any help or comments would be appreciated.

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  • 2grimjim

Posted January 09, 2012 - 10:34 AM


8% leakdown is awefully high for a fresh engine. If you have a good ring and valve seal it should be less than 6%.

You didn't mention what cams you have. If they are YZ spec cams it may be a compression release issue. The YZ compression release doesn't release enough compression for the WR electric starter to function reliably. If it worked when the engine was new but it is hard to crank now, it's probably becaused of the rings taking a set and cranking compression increasing.

You might to redo your leakdown test with a warm engine and see if it improves.

The electric start WR is very sensitive to idle speed, pilot jet size, and idle mixture screw adjustment for the electric start to work well. You also didn't mention if this was a problem when the engine is cold or warm.

Edited by 2grimjim, January 09, 2012 - 10:52 AM.

  • grayracer513

Posted January 09, 2012 - 11:16 AM


Two things to mention at the start:

Leak down testers are not standardized and as such, the same engine may very well put up significantly different numbers on different testers. The only thing one can do with any accuracy is to compare two engines with the same tester, or the same engine/tester combo on different occasions.

Secondly, if I understand the OP, the bike has been set up as is for some time, and was starting normally in its current configuration, and this is a condition that has developed in the meantime.

Does the e-starter not crank against compression, or does the engine crank freely, but not start?

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