Signs of tight valves

9 replies to this topic
  • byw

Posted July 12, 2006 - 06:58 PM


My 01 426 has had some issue's I'm wondering what the symptons would be of tight valves..It won't start when hot and it will kill a plug in short order.Plugs are dry black and sooty.I checked valves a few weeks ago and by me they were in but not really sure how tight the guage should be under cam lobe.I also checked out all electricall componets all are good .Cleaned carb very very good.Jetting all stock bk mod done.Thanks :ride:

  • grayracer513

Posted July 12, 2006 - 07:40 PM


Dry, sooty, black plugs are usually a sign of weak ignition. Try to have the coil output tested.

One sure sign of tight valves is when the clearance measures below spec. Otherwise, weak low speed performance, and hard cold starting, marked by less than normal compression.

  • byw

Posted July 13, 2006 - 02:59 PM


Well I didn't mention it but I replaced the stator,cdi, and coil.Stator and cdi out of a 01 426 used,coil out of a late model wrecked R-1 street bike (stick coil)After changing all this nothing changed.Runs exactly the same.I can run the bike on the stand for 5 min. and it will start to blacken the plug.Could I be that unlucky to have bought bad used parts,god I hope not that would be my luck.Anything that I'm over looking.It will kill a plug in 15 min of riding revved out sounds and runs fine.At lower revs there's a slight popping sound.I'm ready to throw in the towel been trying to figure this out for better then a month.

  • rlp1

Posted July 13, 2006 - 05:11 PM


Has the weather changed a lot recently? Have you changed the oil recently? Changed your riding spot? Checked the air filter? Dry black and sooty but with popping at the low end sounds like a jetting or air circulation problem to me.

  • getdrunk

Posted July 13, 2006 - 06:12 PM


1 of my quads had tight valves. it would bairly start.

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  • tom nolan

Posted July 14, 2006 - 01:46 PM


I might be a float level issue, too much fuel perhaps?

  • 642MX

Posted July 14, 2006 - 03:38 PM


It sounds like a tight valve. Mine fouled a few plugs and was a bitch to start when it was hot. The center intake valve was too tight. I reshimmed it and all the problems went away.

  • SurvivorMan

Posted July 14, 2006 - 04:45 PM


Have you played around with your low end circuit on your carb. Try fattening your pilot jet. Thats the jet (along with a couple others, but this one makes the most difference) that takes care of idle-1/4 throttle. Its easy to get at and change.
I guess I should ask if you have played with your fuel screw first. The fuel screw and pilot work together for bottom end jetting. try asking our very knowledgeable jetting expert in the jetting column

  • MichiganMXer

Posted July 14, 2006 - 07:13 PM


Before you tear that m-fer apart, clean the air filter. If you use too much oil in your filter, it makes it run rich...fouling plugs with the very black soot.

And get some good gas..

It could be as simple as that.

  • grayracer513

Posted July 14, 2006 - 08:16 PM


One sure sign of tight valves is when the clearance measures below spec.

When I said that, I intended some wry humor, but I wasn't joking. If ever you suspect a tight valve, it's one of the easiest things in the world to verify.

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