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CRF 450x won't start (2006) Please Help!!

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Cannot get CRF 450 to even fire under any circumstances.  I've read so many posts, tried so many things including:

Valve inspection and adjustments: Perfect valve seats and clearances - tested and re-tested

Valve Timing:  All 3 marks line up (right crankcase gear, Left flywheel (rotor) mark and overhead cam) Proven Piston is at TDC when doing this.

Leak down test:  In the very good range. 15% leak (Upper green area) of dial.  Air is escaping through rings I guess.  I hear gurgling which i'm guessing is the crankshaft sump.

Spark test : Spark jumps 4mm - New PLug

Impedance tests on coil and stator - check fine according to youtube video

Carb:  Using starter fluid to rule out carb.  .Have also tried with serviced carb

Have even push started by dragging behind car.  No hint of starting.

Any ideas on what to try next?

Clue:  Last time bike started it had been sitting for years, and started with old oil.  Ran about 5 mins then shut off and has never fired since.

The help is appreciated bigly!

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Thanks so much!  Gas is fresh.  It should at least fire with the starter fluid as well.

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Yes, tried kill switch.  I am getting spark when I kick.  Wondering maybe the spark timing is off, but that can't be right?  Just a little starter fluid, usually does the trick to get it to at least fire momentarily.  The plug will get wet after trying to start.  Not excessively though.

Another clue:  When push starting, there is really no way to get the motor to turn.  The rear wheel locks, even in 6th gear.  Like there was too much compression.  Now, when you kick start everything feels normal.  Do I have a problem with the decompression not kicking in?  Jeesh, any motor should turn especially when push starting it in 6th gear.

 

Thanks for the responses.

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It'd be very unusual, but the timing could get off if the flywheel sheared off the key way. But, is the decompressor stuck? It purposely holds open the exhaust valve. If its stuck, it'll never start.

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Take the plug out and cycle the cylinder put your hand over the hole and see if you get an intake and exhaust stroke.

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I've seen the cam slip in the gear and retard the cam timing. Best way to check is to set up a degree wheel and dial indicator and check the lobe centers. also on TDC of the overlap stroke, both the in and the ex valves should be open about the same amount. You can also look at another cam and compare the cam gear marks with the in lobes. If it has slipped, you should be able to easily see the difference.

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If this is a 450X and your battery is charged/starter motor good then try kicking while also pressing the e-start button. Helps heaps with these bikes when they don't want to start. 

Edited by shrubitup

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Thanks all for the great suggestions.  

Yes, I have the appropriate valve clearances when at TDC on the compression.  On the Overlap stroke I will check in and ex openings.  (Thanks James 509!)  I think it's an excellent check on timing issues.  

In regards to the auto- decompression:  I understand it to work as follows (Thanks Shawn_Mc!):  There is a cam roller riding on a cylindrical cam that has a certain gap clearance.  It does not actuate the exhaust valve until it reaches a "speed bump" where it opens the exhaust valve for very brief moment.  I assume this happens in the compression stroke at a certain point where it will reduce the compression as compared to the normal running compression.  (Once the ex valve closes from the auto decompression there will be more compression as the piston is still rising, but it reduces it for ease of starting).  Once the motor starts, this speed bump which is the centrifugal lever's shaft, rotates.  Since it is a half moon pin the speed bump will flatten and no longer actuate the decompression.  

When trying to push start this bike, the decompression must never be engaging, or is engaging out of time; because the bike won't turn the motor (even in 6th gear!) (There is so much back torque that the rear wheel locks) (It still feels normal to kick-start though - it's not locked - The compression is just too high)   So the centrifugal decompression lever is actuating too easily and never decompresses, maybe because the spring is too weak and does not hold the lever in the decompression start-up mode.   (Or it's out of time)

I'll check your recommendations and advise.

 

Again, so many thanks for the great suggestions including using the starter motor to aid in kick starting.

 

autodecompression.jpg

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If it kicks normally but wont fire with a bump start you've got something really funky going on with the cam timing or your bump technique needs work. If you think about the decompressor like a relay or switch, you'd think of it as normally closed, unless the bike is running. You cant kick it hard enough to disengage the decompressor, if you could, it'd probably start from the brute force being imparted (like bump starting).

I'd like to see the timing marks in the stator cover under the little plug. When the T comes up (There are two marks. T for TDC, F for fire. You want the second mark). When the T mark lines up perfectly with the notch in the case, the timing marks will be dead flat across the cam tower split line (with the tensioner set). This is also the position you should check the lash. You should have .006" intake and .011" on the exhaust.

The thing is, even if the timing jumped a whole tooth, which happens regularly, they still run, heck, if you can get them started, they run pretty good. They're harder than hell to kick because the decompressor comes on way late, but they're start-able.

How long did the carb sit with gas in it? What were the circumstances before any of this "it wont start" business?

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Last time it started was with old gas.  Also old oil.  It ran for 5 mins, then conked and never has started again.  All attempts to start it are with either fresh gas or a quick spray of starter fluid.  And nothing, not a hint of wanting to start.  My experience with bump starting is that a large thumper is so "torquey" that the higher gear you use, the less force required to start.  The con is that the motor will rev slower.  But I'm towing it with a golf cart that can go pretty fast.  The issue is the back wheel locks and I can't get the motor to turn, even in 6th gear.  (But yes I can kick start it).  So I concur with you on timing.  I did not know about the T and F marks.  I will check next.  I will try to get some images up on that.  Again, I really appreciate your input!!!

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plugged up carb with old gas.  And what are you dragging it on to try and start?.  If it kind of starts on starting fluid but not on gas then jets are probably plugged accel pump fouled,  This sounds more like carb to me.

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Ok, lets back up the bus here. I re-read your original post. You say the spark will jump a 4mm gap. Thats huge, that's .160", over an eighth of an inch. Now, did anyone ever actually change the spark plug? Those things aint perfect. Ive seen brand new plugs not fire for some reason. Bad resistors inside, etc...

 

What Id do: New plug (again, if you have already), check for spark, with that plug properly gapped. Then, kick it 15 to 20 times to clear all the fuel from the cylinder (ground the plug cap while doing this, no need to tax the coil) Put the plug/cap back, leave the choke off, kick it, or hit the electric starter

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