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2012 CRF250X Valve Clearance Questions

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Bought a 2012 CRF250X new and have ridden it for the last year.  Just now learning I need to check valves.  I have noticed the bike backfiring a lot.  Intake valve is .004 spec is .005.  Exhaust valve is .005 spec is .011.  My question is can, I shim the exhaust value and get a little more riding out of the bike before I do valves or is that to far out of spec.  Should I shim the intake valve or is the .001 okay since it is within spec.

 

Thanks.

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Good rule of thumb is set intake at .006 and exhaust at .010-11 clearance. If your exhaust is at .005 it is way tight and most likely the reason its back firing. Also the valves and seats are showing wear. if this is the case I would adjust your valves before I ride the bike again. Both intake and exhaust. Its better the have the clearance a little on the plus side then tight. 

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The spec is +/- .001, so your set on the intakes.

 

 But I'd double check the exhaust.  They can be tough to measure properly.   A feeler gauge that is bent on the end is the ticket, or I find coming in from the opposite side easier (for the one on the left, I com in from the right side).

 

 The back fire could be nothing more then running lean.  Have you re-jetted as yet?   and have you had the backfire always, or is it something recent?

 

Jim.

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The spec is +/- .001, so your set on the intakes.

 

 But I'd double check the exhaust.  They can be tough to measure properly.   A feeler gauge that is bent on the end is the ticket, or I find coming in from the opposite side easier (for the one on the left, I com in from the right side).

 

 The back fire could be nothing more then running lean.  Have you re-jetted as yet?   and have you had the backfire always, or is it something recent?

 

Jim.

Thanks for the tip on coming in from the opposite side.  That made a huge difference I can slide a 0.10 gauge in with ease and if I push hard and hold the exhaust rocker arm tight against the cam I can get a .011 feeler gauge in on both sides.  So valves seem to be okay and in spec.  I thought something was up that they would be that far off when I was getting the .05 reading.  I have re-jetted.  Put a JD Jet kit in earlier this year.  It backfired before and after the kit.  It is not a major backfire but just notice that my son's 250R never backfires. 

Edited by upontheridge

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Interesting just looked at plugs.  Changed plug before I re-jetted and that plug is tan around the center.  The plug after re-jetting is black in the center. So not sure the bike is running to lean.

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Interesting just looked at plugs.  Changed plug before I re-jetted and that plug is tan around the center.  The plug after re-jetting is black in the center. So not sure the bike is running to lean.

 

 Well good news on the exhaust.   I thought it sounded a bit odd for the exhaust to be so tight and it's a real pain to get an accurate heading with the head wall so close.

 

 As for the plug reading, it's hard to do that well on a modern 4 stroke, but in general, sounds like your approx in the right place with jetting.  However you still can be lean on the slow (pilot) circuit even with the plug looking like that.

 

  So, a few things to check:

 

1. Exhaust is tight, both at the cylinder and at the slip joint in the back.   If fresh air gets sucked in, your going to get popping.  I'm assuming your have removed/plugged the PAIR valve - if not, that's what the problem is.  It injects fresh air into the exhaust in order to reduce emissions.  You'll always have popping if it's working.

 

2. Check the band clamps on the carb, make sure their tight.

 

3. Check the hot start cable, make sure it was free play lock to lock and it's not getting pulled.

 

4. *IF* you've have the slide out of the carb, verify that it's in correctly (it's very easy to put it in upside down).   Note that because of the difficulty getting to this, I'd probably leave this to last.

 

5. Follow the fuel screw adjustment procedure (get highest revs by turning screw, turn idle down, get highest revs again, and repeat until you can't go lower, then bump up the idle a bit).   Once you have that, see how many turns your out.   Less then 1 1/2 turns, you need a smaller slow jet, more then 2 1/2, you need a larger one.   Depending on mods and where you ride, you'll probably be either at a 42 or a 45.

 

   A quick test to see if you have it right; with the bike fully warmed up at idle, if you pull the hot start slightly, it should pick up slightly, and if you pull it more the motor should die.   If you pull out the choke, the motor should die.

 

6. If you still have popping, turn out 1/8 of a turn on the fuel screw and see if that gets rid of it.

 

  Basically, your looking for anything and checking something that will make the slow (pilot) circuit lean.

 

Jim.

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What is the PAIR valve?  Haven't heard of that or done anything with it.  Need to do the fuel screw and idle adjustment again.  Thanks for the list of things to check.  Will plan to look at that this weekend.

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What is the PAIR valve?  Haven't heard of that or done anything with it.  Need to do the fuel screw and idle adjustment again.  Thanks for the list of things to check.  Will plan to look at that this weekend.

 

 Some call it the smog pump... is on the right side up by the cylinder.  Funny looking thing with a few hoses/connections.   Connects to the airbox and exhaust.   It's job is to inject fresh air into the exhaust to burn off any un-burned mixture.  This gives you lots of popping on decel.

 

 You can buy a block off kit, which lets you get rid of it entirely (saves about 1 1/2lbs in weight), or you can JB Weld the passeges.  

 

Jim.

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If the backfire you're experiencing is under engine braking while decelerating, it may be caused by a lean idle circuit. I also run the JD jet kit, and added an adjustable fuel screw to easily fine tune. Try slightly opening your fuel screw and decelerating while in gear until the "popping" is gone. Just make note of your original fuel screw setting in case this procedure doesn't correct your problem. My bike runs very clean w/the CCC airbox mod (top only opened, not the sides), JD jet kit, stock exhaust (I like quiet bikes) and adjustable fuel screw (remote version with a handy turn screw on the side of the float bowl since the X e start motor just under the float bowl makes it difficult to reach the fuel screw). I hope this helps.

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