installed auto decomp cam and fuel screw and now my wr426 wont start...

5 replies to this topic
  • jenham

Posted May 04, 2008 - 05:02 AM


i have just finished reassembling my wr426 after powdercoating the frame and a full motard conversion. i installed the yz450 decomp cam while the motor was out, all valve clearances were slightly out of spec so i replaced them all with CRF450 shims(.025 increments).also changed the fuel screw to an easily adjusted version. now it wont fire?? previously it started first kick every time. i checked the plug before reassembly and the gap was fine,colour was fine. checked the coil with a multimeter, all good. havnt tried bump starting because i have a rekluse so i cant.

one thing i did notice is that there was a lot of fuel being dumped from the lower carb tube???

any advice??

  • ncampion

Posted May 04, 2008 - 06:06 AM


Fuel dumping sounds like a stuck float or leaking needle/seat. Fix that first. Did you check for spark at the plug, if you had all the wires apart, maybe you have a wrong/bad connection somewhere. Are you sure you timed the cam correctly, it's a little tricky as the timing marks no longer line up like stock. good luck.

  • jenham

Posted May 05, 2008 - 12:45 AM


by needle/seat do you mean the fuel screw/oring ???

i actually got it started after a few kicks and disconnecting the TPS, it idled fine and ran fine but i had to kill it pretty quick as i had to go. tried to start it again after a few hours and it was extremely difficult. finally got it to run again and again it ran perfectly untill i put it in gear and it stalled....... then it was impossible to start:censored:

im going nuts:confused:

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  • jenham

Posted May 05, 2008 - 09:48 PM


even though it seems im talking to myself, it helps to say it out loud sometimes.....

finally got it started again, choke in/hotstart in/no throttle/TPS plugged in but it took half an hour of trying to kick it, tipping to drain the float bowl,trying other peoples routines that ive read about on this forum.PITA

warmed it up for 2 minutes, clicked first gear and away i went. it ran extremely well. no hesitation, minimal popping on decel. shut it down and could not start it again:censored:

what are some possibilities that would cause hard starting but not effect it while running?? previously it has started first time every time, only exception being if i dropped it and it stalled, or if i stalled taking off in first..... that situation was also a PITA to restart.

im open to any suggestions??

  • matt4x4

Posted May 06, 2008 - 03:43 AM


Ok, your problem sounds carb or valve related.
If it's valves, then your likely tight on your specs, it's a 15 minute procedure to check that, it's usually NOt a problem that comes on overnight, it's something you'd notice more like a deterioration.

If it's the carb, then it's likely dirty - this could explain the stuck float valve.

The float valve is the valve that is opened/closed by the level of the float, it's like a cone that slips into an orifice, plugging the orifice. This is essentially the valve that keeps letting gas into the bowl as needed to keep the bowl topped up for the carb to function properly. if dirt jams between the valve and it's seat, it'll keep trickling gas into a full bowl and it will come out the overflow tube.

When you start a bike, the carb circuit at play is the pilot circuit, it allows your bike to get a certain amount of fuel (based on the jet size) and a certain amount of air to provide the appropriate air/fuel mixture to get the bike running. The fuel is predetermined by the jet size - the air is adjustable to fine tune using the screw at the front of the carb underneath.

If either the air passage or the jet are plugged or partially plugged, it will affect your starting dramatically.

My first thought would be to take the 17mm drain plug off the bowl, look inside it for debris - this will give you an indication of possible debris getting into your jets. (likely you WILL see foreign matter in there unless you've kept on top of cleaning your carb.).
If there is dirt, I would recommend taking the carb out and thoroughly cleaning it. DO NOT remove the TPS when doing this, however, everything else you can strip off the carb is fair game.
Also remember your EXACT idle and air screw settings - to do so, turn them in until lightly seated and record the number of turns it took to do so.
Also remove and blow out the breather lines coming off the carb - sometimes a plugged line can cause issues.

  • jenham

Posted May 07, 2008 - 12:15 AM


problem solved:applause:

thank you to the 2 that offered suggestions...... it helps alot.

took the valve cover off to check the valve gap which was perfect. so i decided to check the timing and it looked good from the sprocket side but @ TDC the lobes looked suspect. anyway i rotated both cams 1 tooth clockwise which made the lobes look perfect but the timing marks on the intake cam look way retarded(compared to pics ive seen of the decomp cam install). put back together and it fired up with a half ass kick wearing slippers.:eek: :p :applause:

the annoying thing is that i checked the timing 4 or 5 times before i reinstalled the engine and it looked good.

with the benefit of hindsight if doing this mod again i would ignore the cam/head alignment marks and rely on TDC/cam lobes/14 pin count between top cam mark.


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