'03 CRF 450 - won't start???

My '03 Honda CRF450 suddenly became hard to start this past weekend. After 20 minutes of cranking it finally sputtered then fired off. It ran perfect on the track during my first Moto. But, I encountered the same starting problem after allowing the engine to fully cool following the first Moto. I did eventually get it started again and once fired up it ran like a top.

In the mean time I have change the oil, completely drained and replaced the fuel, installed new NGK plug and cleaned air filter element. Now it won't start at all - actually it only makes a loud "pop" from time to time. I have confirmed spark is present by placing the plug beside the cylinder head. At this point I have no idea what to trouble shoot next in order to narrow down as to what the culprit to my strating problem may be. Has anyone encountered starting problems such as these with their 4-stroke (Honda). If so, what was your remedy to the problem? Note: My bike has very low hours (25 +/-) and valves have never been checked or adjusted.

Note: My bike has very low hours (25 +/-) and valves have never been checked or adjusted.

Might want to check those valves. :)

I 2nd that. You've check everything else.


:cry:I have the exact same problem with my bike right now!!

I could hardly get the thing to start I had to give it 1/4-1/2 throttle to get it to start at all then it would not idle.. the next thing you have to look at is the valve clearence on your intake side.. I toulbleshot mine down to that and found that I have no clearence at all on the intake side.. but this sounds like a bigger problem.. go to this site and check this out..


this is a artical that you need to read.. I am sorry in advance it looks like about a $500 job if you do all the work.. but they say this is the best fix for the problem ok so good luck and keep riding.

I hate to say it but I'm 99% sure it's the valves. I'm sure you have no clearance on the intake. Great bikes but the valve issues are a pain in the :)

The exhaust valves were both perfectly "in" spec at 0.011. The upper decompression arm clearance was also "in" spec at 0.014+. The left intake valve measured .004 and the right exhaust valve was not measurable even with the smallest gauge (.0015). According to page 35 of the OM, "If the feeler gauge cannot be inserted, the shim is caught between the valve lifter and the valve retainer. Remove the camshaft holder asembly, place the shim correctly and reinstall the camshaft holder assembly..." Do you know if

this is this a common finding with this bike? And, if so, does it point to a bigger problem?

I suppose this is where I'm at before the next forward mechanical step.

According to page 35 of the OM, "If the feeler gauge cannot be inserted, the shim is caught between the valve lifter and the valve retainer.

The other, more common, reason for that would be no clearance at all. Either way, you're looking at taking the cam assembly off to re-shim the intake valves.

The symptoms of hard starting when cold and starting fine when warm are the common symptoms of not enough intake valve clearance.

Mine became hard to start when cold last month. I checked the ACR gap and the valves, all were in spec (at nearly 200 hours with no adjustment needed, but constant checking!) I noticed that my compression is very high-it turns out that I have carbon build-up in mine. I doubt that is your problem at 25 hours. THe weather fluctuates alot here and I just leave the bike jetted for cold weather-I guess I need to be more fussy, or use better gas.

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