06 YZ450 engine noise

My yz450f has always been a good runner, and is clean jetted, but for the past few weeks it has been extremely hard to start, it will fire right up when cold but after that it wont start well. I figured it was due to the valves being out of adjustment. Halfway through a two hour hare scramble yesterday, which was a complete mudfest, the bike began to overheat due to lack of airflow through the radiators and so much abuse. Any time i stalled or shut off the bike, it took 20+ feverish kicks to start. Today i rode the bike for a minute to warm up the fluids, and after riding for not even a minute the bike was already overheating and clanking. I shut it off to adjust the clutch which took a lot of abuse yesterday, and when i went to start it, it took a minute of hot starting and regular kicking to get it to fire. The clanking in what seemed like the top end was more noticeable than ever. The valve shims were all within tolerance. The oil looked clean, but there was barely a cup coolant in the system, what would cause the engine to clank so loud?

I understand that 4-strokes are hard to start, i also have a wr426, wr450, and a yz250f which dont start half as hard or inconsistent...so im pretty sure it isnt a user issue, there is something wrong, im not sure what. Any advice would be a help...~Trevor~

The crank,connecting rod,wrist pin....

i was afraid of that, have another race this weekend, the noise sounded higher up in the head, what about the starting issues?...thanks

Sounds like a head gasket.

Your motor will sound horrible with little or no water, the water also acts as a bit of a sound insulation. I notice this when I am racing on beaches, as soon as I have been caught or stuck in a jam i can hear the difference with the loss of fluid. I would agree with the head theory possibly leaking.

alright, i will take the cylinder off when i get home from work, could that make it hard to start also?

Is it still the headgasket if the engine oil was clean and without foreign materials?

It sounds like you may just be jetted lean causing the bike to run hot. Once you puke the coolant out, things can start to get really noisy and shitty sounding. What jetting are you running and what's you elevation, temps and humidity?

If your coolant was that low, there is the possiblity that the piston has been scuffed, and the noise you hear is piston slap. See what condition the skirt's in while you have it opened up.

I put it back together and the noise is gone, but it still is hard to start, and it seems like it is running hot. I have a 170 main, 48 pilot, clip is in the 5th slot, and the fuel screw is almost 2.5 turns out...this seems like it is jetted pretty rich to me....the temp is 70-85 degrees when i ride, and the humidity is up there....any suggestions? thanks

check your spark plug make sure its the right kind and that its gapped. you might also need to maybe find a different heat range for your plug. check the carb to see if the filters and such arent clogged. or you could have possible damaged something(gears or other such stuff) and so the metal shavings in the bottom of your engine could be putting more of a strain on the engine. just some suggestions these other guys probably know more of what they are talking about.

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