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Starter doesnt seem to be cranking the engine fast enough?

This is a discussion on Starter doesnt seem to be cranking the engine fast enough? within the Yamaha YFZ450/450R (2004-Present) forums, part of the Performance /Technical category; I have a 04 yfz450. My problem is that the starter doesnít seem to be turning the engine fast enough to start. Its a new ...


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Old 06-05-2009, 01:04 PM   #1
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Default Starter doesnt seem to be cranking the engine fast enough?

I have a 04 yfz450. My problem is that the starter doesnít seem to be turning the engine fast enough to start.

Its a new battery (that tested good), a new starter, the valves are shimmed to .125-.150 on the intake and .203 on the exhaust, the connections are clean and secure without any short or drain on the battery.

My main concern right now is either the auto decompression system or possible a bad new starter.

The decomp seems to be working properly. However, once there is pressure on the decomp pin, it is difficult to move the arm thatís on the sprocket. Once I put enough pressure on the arm, it gives off a "click" sound and will move freely. When there isnít any pressure on the pin (like if the cam was removed) the whole decomp system will move freely. Is this normal?

Any other possible thoughts? Iím out of ideas on what to check next...
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Old 06-05-2009, 03:35 PM   #2
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have you spun the motor manually? does it spin over easily, are you sure the starter isnt spinning fast enough? maybe the whole motor isnt spinning easily.

does it run at all? just not spinning fast?
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Old 06-05-2009, 04:35 PM   #3
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Yeah, it actually runs like a raped ape once I get it going but it just wont start under its own power... I have hand cranked the motor (when I was shimming the valves) and it moves without much force.
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Old 06-05-2009, 04:54 PM   #4
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sounds like a bad starter then.
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Old 06-05-2009, 05:04 PM   #5
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Has anybody had any experience with a PowerSonic battery? The guy at the batter store told me that the PT7B-4 is the one I need. I just looked at the specs and the manual says I need a 6.5 amp battery and the one I bought is a 6 amp. Is that enough of a difference to make it not start?
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Old 06-05-2009, 06:28 PM   #6
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I would have a hard time thinking that .5 amps would make a noticeable difference in cranking, you could try exchanging it or borrowing a buddies and seeing if it changes the cranking speed.
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Old 06-05-2009, 07:30 PM   #7
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there is a CBR battery that a lot of guys use, its a little high amps, you have to cut the divider out that holds the owners manual on your plastics, the battery is just a tiny bit bigger, but its supposed to be a much better battery, i could find out exactly which one if your interested in it.
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Old 06-06-2009, 09:59 AM   #8
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Yeah, absolutely! Thanks for all of your guys help! Still not sure what the problem is but I'll get it sooner or later.

Can somebody with a yfz450 please check to see how much the voltage drops on their battery once they try to start the quad?

The multimeter reads 12.8v when the battery is fully charged. Once I press the start button the voltage drops down to the high 9's or low 10's. The first crank of the engine really sounds labored but ove the initial crank is done the volts go back to the 11's and it sounds pretty much normal. When the battery isnt fully charged (12.5v) the voltage drops down into the mid 7's.

Does this seem correct? I cant figure out why it would drop so much...
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Old 06-06-2009, 10:59 AM   #9
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Sounds like a weak cell in the battery or a bad starter putting a heavy drain on the battery. I just tested mine, and while cranking, mine only drops to 11.3 to 11.5 volts. Also double check all your ground wires and make sure they are making good connections.
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Old 06-06-2009, 11:45 AM   #10
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Thanks a lot! I'm leaning towards the battery right now... Ill try to swap it out with my friends raptor to see if that will start it.

Thanks again!
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Old 06-12-2009, 12:27 AM   #11
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Quote: Originally Posted by leveldrummer View Post
there is a CBR battery that a lot of guys use, its a little high amps, you have to cut the divider out that holds the owners manual on your plastics, the battery is just a tiny bit bigger, but its supposed to be a much better battery, i could find out exactly which one if your interested in it.
Believe its for a Raptor 350 or CBR 600 I installed one in my 07 450. Used a knife and a hand held propane torch to keep the knife hot to cut out the extra plastic. Pretty easy job.
I wanted the extra amps because I installed a Rekluse Pro Autoclutch and there is no push starting if your battery goes bad. Had this happen at Glamis at night with stock battery. Had to be towed by a Bombardier 650. Man that was a wild and fun ride though!
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