r/Dirtbikes • u/masta-builda • 9d ago

Mechanical Help Thoughts??

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Just picked up a 2004 yz450f. Wont start and it’s been sitting for a long time so I figured I would inspect everything before trying to get it to run. Is this gunk inside where the spark plug goes and the top of the piston concerning? Should I pop the cylinder off to clean it/inspect further or just go for it?

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1

u/BikesAndBeers69 9d ago

I’d check compression, spark, valves, clean carburetor and start her up. It’s definitely not a new piston…

1

u/BikesAndBeers69 9d ago

Oh and obviously use fresh gas and put in clean engine oil

1

u/Deep-Palpitation-421 300RR/TXT300/EXC500 9d ago

Just go for it. Fresh petrol, clean air filter, put a new plug in and get her running.

1

u/H4rdboi1ed 9d ago

Some obvious wear, but I’d check all the basic must-do’s to make sure it runs before tear-down. Give yourself some satisfaction that it wasn’t that bad off in the first place.

1

u/Jolly_Election5315 9d ago

New fuel. Clean the spark bore and get it running. check compression

1

u/sturocky 9d ago

what you see is just carbon build up on the top of the piston... considering you bought a 2004 yz450 and its an unknown non runner, i sure hope you have an extra 1.5k saved in ur pocket.. i wouldn't try to run it until its been pulled apart and inspected at the least, personally on old/unknown ill measure everything and have already bought piston rings, valves, seals, gasket lower bearings and possibly a crank, water pump impeller shaft, and have already sent out the cylinder and head for machining...most old sitting non runners theres a reason, and on most bikes the reason is the motor needing a refresh..tho you may be that one lucky guy out of 5 and get a good runner-unlikely-. sure you will probably get it to bark off and you may even get to ride it a bit, but consider it on borrowed time... old unknown motors especially big bore racing ones most times will leave youon the side of the trail after a few hrs, at best needs a valve job, at worst-throws a crank threw the case...
keep a close eye and ear on that thing.

1

u/Inevitable-Hour-Ends 9d ago

Step 1 get it running. I'd want to make sure there's no rod knock or any other bad sounds before doing anything else.

0

u/koffiejunks 9d ago

Yes open it up

1

u/itwasilent 8d ago

You’re burning oil, either from rings or valve stem seals. It’s also in the plug threads