CRF's Only Forums

i recently picked up a 07 Crf450r from a guy who said "the bike just stopped running". when i got it, i tried kicking it over and it had literally NO compression. almost like an 80cc. i cleaned the carb, changed the spark plug, fresh gas and still got nothing from the bike. no pop or any sign of it wanting to start. i tore it apart to check the valves and saw my timing was off a tooth. i advanced it 1 tooth and got the marks lined up for the timing, put it all back together and tried kicking it over. now it's CRAZY hard to kick over! the bike has so much compression that it takes my full body weight (190lbs) and more to even kick it down once. and still it has no sign of wanted to start.. has anybody had this problem before? what can i do to get this beasly bike running before desert season is over? please help...

Welcome to the site !!

You mentioned you were going to check the valves then noticed the timing off , did you check the valves ??? , if so what did you find , was it within spec ??

Also , if it was out of time and you only put it in time and now its really hard to start , does it turn over completely without binding up (like something is hitting ) ?? , if so , did you check the Decompressor is working correctly ?? , if the decompressor sticks or was installed incorrectly , the compression will be like a old Harley and be next to impossible to kick over properly , on these engines , if you do not kick the engine over with force and speed (a full fast stroke) the engine will unlikely fire , it needs momentum to fire , you can't kick it slowly like a 125 , so if the compression is preventing you from kicking properly , that "might" be the reason why it did not start


What i would do is recheck the valve lash , and remove the spark plug and turn the engine over by hand and watch closely at the valves , make sure they are opening and closing correctly and fully , make sure the lash is correct , and triple check the timing and function of the decompressor , if the bike is in time , and the engine has Spark , Gas , and Air , , and there is no damage from valves hitting piston (from timing being off) it will run

Welcome to the site !!

You mentioned you were going to check the valves then noticed the timing off , did you check the valves ??? , if so what did you find , was it within spec ??

Also , if it was out of time and you only put it in time and now its really hard to start , does it turn over completely without binding up (like something is hitting ) ?? , if so , did you check the Decompressor is working correctly ?? , if the decompressor sticks or was installed incorrectly , the compression will be like a old Harley and be next to impossible to kick over properly , on these engines , if you do not kick the engine over with force and speed (a full fast stroke) the engine will unlikely fire , it needs momentum to fire , you can't kick it slowly like a 125 , so if the compression is preventing you from kicking properly , that "might" be the reason why it did not start


What i would do is recheck the valve lash , and remove the spark plug and turn the engine over by hand and watch closely at the valves , make sure they are opening and closing correctly and fully , make sure the lash is correct , and triple check the timing and function of the decompressor , if the bike is in time , and the engine has Spark , Gas , and Air , , and there is no damage from valves hitting piston (from timing being off) it will run

thanks for the awesome reply JimDirt !

How do i set the Decompressor? yes i checked the valves and everything looked fresh and good. but I've read a few forums now and I'm starting to get curious about the decompression thing. how does that work and how can i check to make sure that's not messing me up?

On your year it is non adjustable , it is located on the end of the cam in the center of the sprocket and goes inside the cam itself as well , it is comprised of springs and a detent pin/plunger located on one of the exhaust lobes of the cam , your concern is that everything is working freely and that nothing is broken , sometimes the pin shears or gets stuck , sometimes the spring breaks or gets bound up and it won't release , the decompressor is actuated by centrifugal force , and it slightly holds a exhaust valve open to lessen the compression while kicking the engine , so its not like kicking over a 1949 Harley , and is supposed to do the opposite of what you are experiencing while kicking

I can post some pictures from the Factory Service Manual if needed , but i would also recommend if you're going to keep this bike and work on it , to buy a Factory Service Manual , so you know what exactly to do and have all the correct specs and tools while performing maintenance , you can get one here (just choose your year from the drop down list) https://www.crfsonly.com/catalog/produc ... ts_id/3226

Or you can buy/order one directly from your local Honda Dealer

We are still here to answer any questions even if you do get a manual , as sometimes even if you do have the manual , things can get confusing , or there are shortcuts to doing things that can save time and money that are not listed in the manual , and the people here have either posted them already here , or can answer any questions you have directly in these forums

If you need a few guideline pictures , i can post them , i just have to upload them to my hosting site , so it may be a bit