450f locking up!!

I just finished changing the head gasket on my 04 yzf450, and on the first ride, I was only out about 5 minutes just kind of blipping the throttle when it locked up and died, skidding the back tire. I immediately pulled in the clutch and coasted to a stop. I could turn the engine over by hand no problem, but just pushed it home. I double checked my timing, which was still spot on, and pulled the spark plug, which was very light in colour but otherwise in good shape. I re-assembled and started it after changing the oil(no chunks) and making sure the oil pump was working. It fired right up and ran fine, so I headed out for a little ride. I got about a minute down the trail with it running fine, I gave it about 3/4 throttle cresting a little knoll, when it did the same thing. As before, I clutch it and came to a stop, and tried kicking it over. It fired right up and ran perfect. I did notice that the drive chain was fairly loose and slapping. Anyways, I rode it home at about 1/4-1/3 throttle and parked it. I have tightened the chain, but I am a little nervous to ride it now in case it is something seriously wrong internally. Could it maybe be that the loose chain was snagging the case gaurd(no obvious damage) or the rear chain guide? Or could it be something in the tranny? I have only had this bike for a week, and the decomp plug on the head has blown out, I've had to change a head gasket, and now this. Needless to say, I'm a little frustrated. :applause:

I would appreciate any advise/words of wisdom

thanks

Did you check:

1) Your coolant (did you remember to add it?)

2) that the oil pumps are indeed working (loosen an oil line with it idling and look for oil).

Just my immediate thoughts..

The coolant was good (full). And after I changed the oil, I made sure that the oil was making it up to the frame resevior. As it was empty before I ran the engine and full after I ran it for a couple minutes, I assumed it was alright.

thanks

Why did the head gasket need changing?

If you are the second owner---did first owner recently change the piston?

What happens when the bike would idle for the same amount of time that you rode it?

The head gasket was leaking & pressurizing the cooling system, causing it to spit coolant out the overflow. No recent piston change, supposedly low hours and well maint. Idling seems fine, and I can play with the throttle in nuetral or with the clutch in, with no probs.

There are 2 oil pumps; one to put oil into the frame, and one to take it from the frame and pump it around the motor. Sounds like you're sure the first pump is working, but be sure to check the second pump too by loosening the oil line while it's idleing.

Has it got a complete set of teeth on the cog at the bottom of the timing chain?

I will check for oil flow today. I haven't inspected the bottom timing drive, but being that the timing is still good, I would think it's alright, no?

I just finished changing the head gasket on my 04 yzf450, and on the first ride, I was only out about 5 minutes just kind of blipping the throttle when it locked up and died, skidding the back tire. I immediately pulled in the clutch and coasted to a stop. I could turn the engine over by hand no problem, but just pushed it home. I double checked my timing, which was still spot on, and pulled the spark plug, which was very light in colour but otherwise in good shape. I re-assembled and started it after changing the oil(no chunks) and making sure the oil pump was working. It fired right up and ran fine, so I headed out for a little ride. I got about a minute down the trail with it running fine, I gave it about 3/4 throttle cresting a little knoll, when it did the same thing. As before, I clutch it and came to a stop, and tried kicking it over. It fired right up and ran perfect. I did notice that the drive chain was fairly loose and slapping. Anyways, I rode it home at about 1/4-1/3 throttle and parked it. I have tightened the chain, but I am a little nervous to ride it now in case it is something seriously wrong internally. Could it maybe be that the loose chain was snagging the case gaurd(no obvious damage) or the rear chain guide? Or could it be something in the tranny? I have only had this bike for a week, and the decomp plug on the head has blown out, I've had to change a head gasket, and now this. Needless to say, I'm a little frustrated. :applause:

I would appreciate any advise/words of wisdom

thanks

It sounds like at small throttle openings everything ok. But at higher throttle openings you have problems ---main jet too small causing a lean condition? Maybe piston is expanding too quickly in the cylinder due to lean main jet???

new2blue, I tore the engine down, and there is not a mark anywhere. Not on the piston, cylinder, clutch, all the gears in the tranny look good. Also, it has happened with a 172 main, as well as with a 165 main. I don't really want to put it together without finding something, but I'm stumped.

It sounds to me as if the bike is just dying. With the compression as high as it is, it will feel like it's locking up, but actually not. If it was anything else I believe you would see physical damage by now.

It runs fine at lower RPM's, but fails to run while on the gas?

I would think the CDI isnt supplying enough juice under power, but that wont cause the motor to lock up.

-Does this happen in only one gear or has it been random?

-You said it happened when you 'blip' the throttle. I assume that you are at low RPM's when you blip it and the fuel is coming through the pilot circuit. What size pilot is in there and where is the needle at?

I was in 3rd gear both times. Pilot jet is a 45, 72 starter, 172 main, and the needle is in the middle position.

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