07 decompression mechanism help

[RedRider501]

I recently bought a used 07 crf450. When I went to look at the bike the owner started it up, only took one kick, and it ran great. I got it home and kicked for about 45 minutes and it never fired. I drained the gas, put fresh 93 octane in it. cleaned the air filter, new sparkplug. I got it to fire after kicking for about 20 minutes. The kickstarter is extremely hard to kick. I thought valves may be out of adjustment so I pulled the valve cover and all the decompression stuff is gone. He said he recently put stainless steel valves in it, so I guess when he did that he didnt put the auto decomp stuff back in for some reason. So I ordered some parts on ebay, but it looks like the decomp base/weight has a long allen bolt that goes through it into the camshaft. I dont see anything for the bolt to thread into in my cam. All I see is a dowel going through the center of the cam. How does this attach to the cam? I looked at the microfiche and it didnt really show anything. Sorry for the book. Its just depressing to buy a bike and run into stuff like this from the getgo.

[MELK-MAN]

i don't think you know what your looking at, take the valve cover off and post a photo of the cam gear. That is where the decomp mechanism is for the 07. Then order a manual. The decomp is WAY different on later models than early models. There is nothing on the right end of the cam, that is why you might think it is gone.

If the decomp was gone, you would NOT have been able to kick the bike for 20 min.

There is a weight on the cam gear, you whould be able to move the weight back and forth on the gear, and see it actuate a lever that runs inside the cam that actuates the decomp to the exst valves.

It could be you just don't have the starting technique down yet.. they take a squirt most of the time, but if you flooded it.. sure, it would not start for a long time.

[RedRider501]

It is very possible that I dont know what Im looking at. There is a weight with a spring attached to it on the cam gear that turns a shaft inside the cam which moves the dowel pin in the center of the cam. Whats throwing me off is there is a hole in the cam holder for the decompression arm like Ive seen in pics of other bikes online. I dont understand why Im 210 pounds with strong legs and when the bike gets to the compression stroke I cant budge the kickstarter. I just have to stand on it with all my weight and let it slowly get past the compression stroke then I can kick it.

[JJRace]

look at the sticky at the top of the page on timing the crf450r. it will show you a 07/08 decomp cam

More than likely your carb is plugged. You need to clean the pilot jet out. then check the hotstart piston in the carb, clean it, lube it and make sure there is play in the cable.

[RedRider501]

Ok so I was wrong about the decomp. I didnt know the 07 had a different style than previous years. The guy before me ran rotella 15w40 oil in it, I changed filter and oil to honda 10w40 synthetic. After a few kicks it started to get alot easier to kick. About to what I would call normal. It still wont start. Im gonna go clean the carb and see if that helps. I checked the sparkplug, Its firing good when I hold it against the frame and crank the engine. Thanks for the help.

[Rocksalt]

Check your cam timing. If you are off a tooth it will be hard to start.

When starting the bike slowly move the kick to where you feel compression. Keep pressure on the kick starter and it will give way then stop. Move the kickstart to the top and give it a full kick. Should start in one kick if the fuel mixture is right on the low speed.

[MELK-MAN]

Ok so I was wrong about the decomp. I didnt know the 07 had a different style than previous years. The guy before me ran rotella 15w40 oil in it, I changed filter and oil to honda 10w40 synthetic. After a few kicks it started to get alot easier to kick. About to what I would call normal. It still wont start. Im gonna go clean the carb and see if that helps. I checked the sparkplug, Its firing good when I hold it against the frame and crank the engine. Thanks for the help.

.. your wasting your money on the expensive honda synth. MANY use Rotella, it is very very good oil. I have a thread with a photo of my original cylinder that had nearly 900 hours. No issues, pretty much in spec but i replaced it.. but sold it and it is running well in anothers bike. not to get off topic, sorry.

Cleaning the carb won't change your compression. be sure when you look at the pilot jet that you inspect/clean the 8 holes on the side AND the thin hole that runs right down the middle.

As JJ mentioned above, it is possible the timing is off 1 tooth that is causing your high compression issue.

[RedRider501]

Ok I cleaned the carb. Everything looked good, didnt see no clogs but I cleaned it anyway. Timing marks are lining up like they should. The last time the bike ran for me I had forgot and left the fuel petcock off and it ran out of gas. Havent got it to start since. Its acting almost like a diesel engine when in runs out of fuel, like it isnt primed or something. I kicked for 15 minutes and pulled the sparkplug out, it still looks as new and white as when it came out of the box, not wet either. I guess Ill try to find a long hill and roll down it and try to start it that way.

[sick 96 250]

what is your procedure for starting it? Besides just kicking the crap out of it, do you choke it, twist the throttle a few times prior, etc?

[RedRider501]

gas on, choke on. slowly push kickstarter until motor is at TDC, let kickstarter come all the way up, then kick hard all the way down. Been doing that 5-6 times, then a couple twists of the throttle, repeat. Ive busted the sole out of my rocky boot kicking it so much.

[MELK-MAN]

you looked under the valve cover from what i read in your first post.. but did you actually measure the clearances?

[idsmokeu2]

Don't give it any gas goober.. It's got accelerator pump that will do it for you... Only give it one initial turn on the gas else your going to flood it..

[MELK-MAN]

Don't give it any gas goober.. It's got accelerator pump that will do it for you... Only give it one initial turn on the gas else your going to flood it..

? umm.. ya gotta twist the throttle to make the a.p. squirt.. LOL THere is a small rod that runs down to the ac diaphram, it is actuated by a cam when you twist the grip. It ain't automatic ?

I give my bikes a good twist or 2, pull the choke, get the k.s. near the top and a good swift kick. Usually 1st or 2nd kick will get it started as long as the valves are in spec. If real hot and i need to restart immediatly, i may use the hot start but usually never need to.

[RedRider501]

Ok so I got the bike at the top of a steep hill. Got it rolling and as soon as I popped it in 2nd gear and released the clutch it started. Didnt have to give it any throttle. It runs perfect, idles great. No bogging, hesitation, backfiring, nothing. But after warming it up I shut it off and still cant kickstart it. So Im leaning torwards valve adjustment now. I checked them when I had the valve cover off. exhaust valves were .009" and .010" the intake was .005" and .004". I know thats slightly off spec but I didnt think that was enough to keep it from starting. It wont kickstart period, hot or cold.

[MELK-MAN]

they be tight. not zeroed out, but not in spec. Bumpstarting easily is classic tight valve situation as your bypassing the decomp. the motor spins over fast enough to not actuate the decomp..

[RedRider501]

Im glad I finally found what the problem is, hopefully. Ill order a shim kit and a micrometer. The valves that are in it are kibblewhite SS valves and I dont think they have been shimmed since they were installed.

[JJRace]

also the carb could still have issues. Hotstart plunger?? did you inspect it? Did you blow out the jets?

this is a new bike to you so it may not be running so perfect. You just dont know any different.

[RedRider501]

I blew the jets out when I had the carb apart. I didnt really examine the hotstart plunger. I didnt figure anything was wrong with it. When the bike is running and I pull the hotstart lever it pops, cracks, and backfires. Without it pulled it runs smooth.

[Rocksalt]

It could be that you are not using the correct starting procedure. These bikes are sensitive to A/F mix. Using the choke or accidently twisting the throttle will not get the bike started.

Usually you can twist the throttle and try and start it, no choke. If it does not fire off hold the hot start in and kick it. Learning what the bike needs for starting is a trick in itself.

If the fuel screw is not set properly you will have trouble starting.

Get the bike started and do the "idle drop method" to set the pilot circuit. Once completed properly the bike should start with ease.

Don't get affixiated on valves! When the valves are being held open the kickstart will move with your hand. The bike will run fine with .004 intake and .008 exhaust. Usually when the valves are being held open it happens when the bike is hot due to thermal expansion of the metal. When they hold open the bike will run rough, backfire and may not run at all.

It took me a bit to understand what to do when the bike won't start to see if the mixture is lean or rich. You will have to do the same.

The reason the mixture is so critical is because of the decomp system. The cranking compression is sub 100PSI (usually 75LBS). Not many motors like to run under 100PSI so the mixture needs to be very close.

[RedRider501]

one more quick question. What color spark should the spark plug be producing? I took the plug out and grounded it against the frame and cranked it over fast as I could by hand and its making a purple spark. The old sparkplug is the same. I thought it would be a bluish/white spark but I really dont know.