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Crf 450 2004 need answers

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I have recently had a rebuild ( picture ) and there's not much compression as it's easy to kick over. What could it be?

Also I had the valves checked and was told they were in spec, yet it's hard to start when hot, does it need re-shimming?

Finally, it bogs quite a lot. When I snap the throttle back while at idle and pulling off/out of corners without high rev's. Would the ap mod help this?

Other than these, it's goes quite well.

Any help would be appreciated.

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Could be they got the timing off one tooth. Or the decompression lever needs to be set up correctly. Has the carb been worked on as well?

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Before the rebuild I messed about with the carb settings but the shop re set them and fitted a fuel screw witch I have not touched since. I don't think the timing is of because it runs fine when started and it starts with 1-2 kicks from cold.

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Before the rebuild I messed about with the carb settings but the shop re set them and fitted a fuel screw witch I have not touched since. I don't think the timing is of because it runs fine when started and it starts with 1-2 kicks from cold.

Ive seen motors do exactly what your saying and  be a tooth off. Little hard to start and a horrible bog out of the corners but other than that runs fine? I seen a guy replace his entire electrical system trying to chase these same symptoms only to fine out it was a tooth off.

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Mine is only hard to start when hot, could this still be a tooth out or am I looking towards valves?

Cheers

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Key is low compression.  Hmmmm how low?  I think the spec is 78psi, due to the decompression lever!  Actual compression is much higher.  Still should be hard to kick over.  I hate to say this, but I never trust a shop.  too many small things missed (forgot to tighten this or that).

 

  1. +1 on timing  If you are not mechanically inclined  this is still very easy as long as you can remove the plastics, seat and tank, you have the skills to take it the rest of the way.  I have a manual if you need it.
  2. +1 on carb needing to be cleaned...again, or it at all.  My 2005 was a bitch to start cold, cleaned carb (starter jet) and now its great. Again this is pretty simple stuff, since its all plug and play inside the carb.  You should only need to use compressed air for cleaning and maybee a bit of fishing line for the pilot hole where it enters into the throat.
  3. +1 on the decompression lever not adjusted correctly.  Needs 0.35 mm plus 0.28 mm at the valve (if my memory is correct).  Thats a huge clearance and if the mechanic was not thinking may have forgot to do the simple math needed to get both close to 0.65 or what ever the spec is.
  4. Check plug is screwed in LOL  but seriously
  5. Check carb boots make sure they are on correctly, particularly the air box to carb one.  It can be tricky to get in on all the way, since its pretty hard to see if it fits.  Not impossible by you need a flashlight and several angles.
  6. Make sure hot start cable is not too tight at the lever on the handle bar, and that the attachment on the carb is screwed in all the way.  make sure its not pulling with side to side movement.  set the fuel screw to 1.5 turns out, or what ever the manual says.
Edited by bikedad1

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Thanks for the info!

I have a manual and I can do little things like valve clearances but I don't

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Want to mess something up as i've just spent a lot of cash on the rebuild. I have only been out on the bike for about 40 mins since. Having the time to sit down and have a go at fixing it is the problem as I'm very busy with work. I will see if I can have a look at it and let you know what I find and go from there.

Once again, thanks for the help !

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Just managed to have a look at my bike and look what I found!ImageUploadedByThumper Talk1380299080.349203.jpgImageUploadedByThumper Talk1380299095.036424.jpg

Correct me if I'm wrong, but this is out right!

Could this be the reason for not starting when hot? Didn't manage to check valve yet as the mrs needed to go to work, but that's the next thing to look at!

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Just managed to have a look at my bike and look what I found!attachicon.gifImageUploadedByThumper Talk1380299080.349203.jpgattachicon.gifImageUploadedByThumper Talk1380299095.036424.jpg

Correct me if I'm wrong, but this is out right!

Could this be the reason for not starting when hot? Didn't manage to check valve yet as the mrs needed to go to work, but that's the next thing to look at!

The way the cam sets in that picture it appears to be a tooth out....But before jumping to a conclusion make sure you line the mark up on your flywheel. DOnt go based off the timing dot on the clutch side. That is only used to get your flywheel mark close enough to find. If your flywheel timing mark is lined up and your cam is still setting like this...then yes you are a tooth out

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I have lined them up in the picture using the primary drive gear in the crankshaft hole, then the marks on the cam sprocket and the camshaft holder as shown in the manual.

If there's another way please let me know as I just want to make sure it is all timed properly. Cheers

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Thats one tooth for sure. Do yourself a favor though. Dont bother with that crank side plug too much other than turning the engine over with a wrench. Use the other side of the engine, the timing cover hole. The marks much easier to read. 

 

Check the sticky I put at the top of the forum. 

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I know on my RMz that their are two marks, one for timing advance and one for TDC.  The TDC is the second mark that comes around (its about 1cm away for the timing advance mark) when rotating counter clockwise.  Can't remember on my CRF, but you have to be careful with the RMZ that you get the right mark and on some bikes, holding at TDC, exactly is a very delicate operation since the piston can be pulled off TDC with a tiny nudge or bump.  Just be careful and double check everything.

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Just checked the valve clearance and here us the results:

Left intake .006 right intake .006 ( in spec )

Left exhaust .011 right exhaust .009 ( right exhaust is out of spec )

Decompression clearance .005 ( out of spec )

So next thing is to buy a tool that measures shims, can't remember what they are called.lol. Then buy the right shim and install it.

Once I get my right exhaust back in spec, correct me if I'm wrong but the decompression clearance is .025? I do have the manual but just wanted to make sure.

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I work in milimeters sorry can't verfy inches with out checking manual. 

 

Did you figure out that the clearance measured at the decompressor is decompressor + exhaust valve.  So you measure exhaust valuve clearance (EVC), measure  decompressor clearance (DC) and then do a bit of math.  At least it is on my 05.

 

Total clearance measured at DEcompressor = EVC + DC

DC= total clearance - EVC

 

Tecnically you do not have to measure the shims, since they are marked (unless marks have worn off your old shims).  Next step is to extract your old shims, before you get new ones and figure out what size they are and then do a bit of grade 7 math, which strangely enough requires a bit of thinking!  THis will allow you to target the shim sizes that you need to buy. 

 

I think you are right, its wise to buy calipers (digital) is easier and I got a pretty good pair for 20bucks on sale.  You can pay 100 or more, so shop around.  You will really need these if the numbers are worn off your old shims.  When shims go in, rule is number up, bit of oil on them, then rotate engine to squish oil out from between lifter and tappet, then set TDC and  remeasure.  Does not hurt to oil up the cams and other stuff once your ready to sew it all up.

Edited by bikedad1

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Ok, so the next step is to get some calipers and work out what shims I need ( only one but will double check ) and hopefully get the valves back in spec.

Once this is done, if this does not stop the hard hot starts, where do I look next?

Once again, cheers for your help!

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