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pez 04 yz450f

HELP! think i might have got burned

20 posts in this topic

Hopefully someone can help me out here! I just bought an 04 yz450 and the guy said "it ran great last summer" but it sat all winter and we couldnt get it started. it had spark but it was harder than normal to kick. my mechanic says its something in the engine or clutch but cant tear into it without charging me. has anybody had this happen or know what it could be?

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Yeah it was in neutral and the oil was changed. I used to be all about 2 strokes until I rode a four stroke and ill never go back! But this is only the second four stroke I have owned and don't know a whole lot about them. It was super hard to kick so I'm thinking the compression is good and my mechanic says its only 10psi. Does that still sound like valves? Do you think the just need adjusted or could there be bigger problems?

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If it were hard to kick the compression would be to high, not way to low like 10psi... If the valves are to tight could be rubbing the cam lobes and causing it to be harder for the piston to go up and down therefore harder to kick...

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Hot start is kind of a reverse choke.

The decompression release is inside the head.

Harder to kick would mean more compression.

Valves are probably out of spec.

After working on a 4 stroke, I'll never go back lol

Edited by DevinMx7

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If you paid a guy good money for a bike you couldn't hear running and took his word that it ran good then your the 1 who burned yourself,that being said I think you need to get it to someone who knows what they are doing as by your questions it seems you don't know these bikes very well.I know its nice to do things yourself and feel the accomplishment but there comes a time when you have to bit the bullit.If your interested in repairing these bikes then find someone who will let you watch and learn.First thing to check is timing,pull the plug and see if its still hard to turn over.If it still hard then your into something starting to seize,did you notice it turning good then locking up?If timing is off enough the valves will hit the piston.

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If you paid a guy good money for a bike you couldn't hear running and took his word that it ran good then your the 1 who burned yourself,that being said I think you need to get it to someone who knows what they are doing as by your questions it seems you don't know these bikes very well.I know its nice to do things yourself and feel the accomplishment but there comes a time when you have to bit the bullit.If your interested in repairing these bikes then find someone who will let you watch and learn.First thing to check is timing,pull the plug and see if its still hard to turn over.If it still hard then your into something starting to seize,did you notice it turning good then locking up?If timing is off enough the valves will hit the piston.

This! You made a big mistake buying a non running bike and are in way over your head. Get help, you have no business touching that thing. Don't make things than they already are.

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I paid $800 for it knowing I was going to have to put more into it. I was unsure of how much though. I never worked on four strokes just two strokes and from the sounds of it four strokes are alot more difficult to work on. I have a mechanic getting ready to start tearing into it but I love the advice an feedback from these forums and would like to learn alot about the bike.

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get yourself a manual

Check your timing chain tensioner. I'm not familiar with your bike, but ya might wanna pull the cover(s) and view the timing chain mechanism.

Edited by Slackkinhard

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If it has freakishly low compression (10psi), either the gauge is busted, a valve/s is open, or the spark plug is out... After cleaning the carb, spray a little wd40 into the spark plug hole, and kick it over (with the plug out). This should seal the rings a bit. Put the plug back, see if it has compression. If yes, try to start it. If not, check valves/timing, and for the love of god, get a manual and a friend to help

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I paid $800 for it knowing I was going to have to put more into it. I was unsure of how much though. I never worked on four strokes just two strokes and from the sounds of it four strokes are alot more difficult to work on. I have a mechanic getting ready to start tearing into it but I love the advice an feedback from these forums and would like to learn alot about the bike.

Before you have a guy tear into it and spend good money what do you mean "a little harder than normal"? What are you comparing it to? I own blue and can tell you that some of the earlier 4Ts were bears to start both cold and hot. Take the advice of the guys and change the oil, drain the gas, clean the carb, check the exhaust , then get a manual or go online get the right tools and adjust the valves if it is still a problem then look at more complex stuff . You could do things a step at a time and see if it helped but I would definitely do the oil gas and carb first. Have doubts about your mechanic's conclusions if your quotes are anywhere near correct BTW.

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Thanks guys appreciate all the feedback! I'm going to check the gas in the carb, valves etc and ill be back in a day or two. Again thanks for the help!!

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you are pulling the decompression lever in right.you can kick them over without but its hard as hell to start the stroke and i got some bigass legs and not the fatty kind good luck and welcome to 4 strokes happy learning

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All advice is good,I'd say either the rings are low or the valves need work.

You can download the manual from Yamaha & have it printed by going to HERE

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