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Old 04-29-2004, 10:30 PM
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Default Backfiring and hard to start CRF?

Hey Ya

Haven't had any problems with the CRF until now. Been riding it since Nov 03 and the last two rides I've had some problems.

First off: It takes over fifteen kicks to get her started from a cold start. Before these last two times never more then four. My procedure has been 1. Pull choke. 2. turn on fuel 3. start her up (don't touch throttle).
After she was started and warmed up and everything it never took more then two kicks to get her back to life in the same ride. Now it takes another ten kicks to get her started. The key to this is nothing has changed over the last two rides. I ride at the same track the same times with the same weather. The bike was jetted perfect out of the box and haven't needed to change any of those.

Second thing: It's starting to backfire after letting off the throttle. Two sections of the track I hit third gear pinned and when I let off it back fires pretty bad and if I drop her down to second to get some engine breaking it's twice as bad.

I'm pretty new to the four stroke world and I'm a little ashamed to say I haven't touched a thing on the engine since I've owned it. I know valve adjustments are coming but didn't think I would need it this soon. I ride tracks mostly at a novice level so I get the thing moving but it's not a daily thing.

Anybody have some ideas, it would be appreciated.

Thanks
Greg

04CRF450
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  #2  
Old 04-29-2004, 10:55 PM
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Default Re: Backfiring and hard to start CRF?

Just a guess, but i'm going to say your valves are tight. Have you checked them?
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Old 04-29-2004, 10:55 PM
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Default Re: Backfiring and hard to start CRF?

Oh, and the hard starting is exactly what happens when the valve clearance goes to 0
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Old 04-30-2004, 12:06 AM
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Default Re: Backfiring and hard to start CRF?

My Yamaha thumper starts first Kick!! What I do for a cold start is give the throttle two LITTLE blips. Only for cold starts, seems to work great!!! remember, LITTLE blips, not the whole way!!
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  #5  
Old 05-01-2004, 10:31 AM
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Default Re: Backfiring and hard to start CRF?

i heard if you even blipped it a little bit it has a chance of flooding, oh well

yeah it sounds like your valves need adjusting, this isnt hard to do...in fact i have an article on the crf250r and valve adjusting(i read to many magazines)

Step 1) It is always wise to start with a clean bike since internal engine parts will be exposed. Try to get the top of the engine and the area under the gas tank as clean as possible. Remove your seat and gas tank to expose the valve cover on top of the motor.
Step 2) Use compressed air to blow out the spark plug hole before removing the spark plug cap, then remove the valve cover. On the Honda CRF250R you need to remove two 10mm bolts to remove the cover.
Step 3) Now that the head is off, it is time to find top dead center(TDC). On the CRF250R the easiest way is to use the kickstart to turn the motor over slowly. Once you hear the decompression lever "click", you have found TDC. The cam gear will have two flat marks that will line up with the top of the head. Every brand will use different marks on the cam gears to locate TDC. Please refer to owners manual for the proper technique for finding TDC. If you try to measure the valve clearance at any other location the measurements will be off and there is a chance of making a costly mistake.
Step 4) First check the intake valves which are the two or three closest to the carburetor. Using a feeler guage, slide the appropriate petal between the cam and the valve. Do not force the petal in; the fit should be nice and snug. Refer to owner's manual for proper tolerances. On the crf the clearance should be between .004 and .006 thousandths of an inch or .09 to .15 hundredths of a millimeter. If your ride doesn't fit these standards, the cam will have to be removed and a different sized shim must be installed.
Step 5) Using the same method, check the two exhaust valves. All brands except the hondas will have a cam above the exhaust valves and look similar to the intake side. Hondas only have one cam, so they need a rocker to open the exhaust valves, but the feeler guage is still placed between the valve buckets and the rocker arm. The crf specs for the exhaust are .010 to .012 thousandths of an inch or .25 to .31 hundredths of a millimeter.
Step 6) Now that it's confirmed that the valve clearance is up to par, the valve cover, spark plug cap, tank, and seat can be installed back onto the bike and you're ready to ride!
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Old 05-01-2004, 10:32 AM
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Default Re: Backfiring and hard to start CRF?

it looks scary hard but once you read it over its pretty simple if you have the tools
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Old 05-01-2004, 10:45 AM
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Default Re: Backfiring and hard to start CRF?

Mine has always started great. I have just noticed it back firing sometimes when I started it. That is what got me to check valves.
The checking part is pretty easy to do. The tear down to remove head and cylinder where really simple , just read and follow directons.
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Old 05-05-2004, 12:49 PM
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Default Re: Backfiring and hard to start CRF?

I hate to say it but it sounds like your valves went to zero clearance. Pull the valve cover off and have a look see.

The starting problems you're having definately sound like valve issues, but I have had similar problems due to a plugged pilot jet. Maybe pull it out and see if you're got anything plugging it.

Also, a friend of mine had similar problems when the fuel screw backed out too far and fell out. The bike would still run but ran poorly - as if it was running very lean.

Backfiring when letting off the throttle can be a lean condition, but I would check the valve clearances before you start chasing jetting problems.
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Old 05-05-2004, 11:33 PM
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Default Re: Backfiring and hard to start CRF?

Thanks for the input, guys. I followed your directions (and the manual) and everything was within specs. I ended up changing the spark plug and guess what? It fixed it. Well at least I learned how to check the valves.

It helps when others convince me it's not as hard as I think it is.

Thanks again
Greg
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Old 05-05-2004, 11:40 PM
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Default Re: Backfiring and hard to start CRF?

Cool. Glad to hear it wasn't your valves. LOL.
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Old 05-05-2004, 11:44 PM
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Default Re: Backfiring and hard to start CRF?

Me too! Good job.
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