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Other ATV\'s => Other ATV's => Topic started by: xTHUNDERCATx on June 10, 2014, 12:52:08 PM
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I'm throwing around the idea of adding a YFZ 450 to my collection (that electric start has been tempting me for a while). Something for a decent back up bike but I figured I would jump on here to see if anyone knows of any major issues that came up with any of the years or anything that has a bad reputation I need to be watching for.
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early years had to have the oil mod done to cool the bottom of the piston. lots of issues with the throttle over ride system and throttle position sensor also, although those can just be taken off.
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We raced an 04, still racing it, since 2007. No oil mod done, no throttle issues and I do all the servicing on it year after year and the valves are in spec each and every time. I don't know if we got lucky or what but it flat out rips, gets the holeshot every time and it's a bone stock engine other than the cam mod. If you set the carb up properly with no stupid zip tie mod and jet it properly it never has a bog issue....ever. Key is the leak jet and needle. They are dirt cheap to find and parts are almost as easy if not easier than finding honda parts. If you do decide to get one find an 07 and up as it does have the oil mod done and the suspension on the rear is a little better.
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My dad has the 07 and it runs well with just a pipe and intake
Plenty of torque ,recently dropped a few teeth in the rear for a lil more speed
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[MENTION=66]bholzgen[/MENTION] what yr was racer Dave's? 04? Cuz that thing ripped as bone stock. Almost 330r fast.
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Get a yzf hybrid instead! Lol
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Alrighty so i picked up an 06. Heres the current situation when i went to look it fired right up initially it would bog hard if i revved it quickly (had to be eased on) I was test riding it opened it up and she died and wouldnt fire back up, decided to gamble and bring it home anyways for a better price. I pulled the carb and it had a clogged pilot and was layered with yellow gunk (bike sat for a while according to him) i got new fuel in it and she fired up today. i had it idling for a minute when i blipped the throttle. It bogged like it did initially, back fired and shut down now she wont fire up. What are some thoughts, im going to replace the plug tomorrow, if it has good spark im guessing for some reason it isnt getting fuel but i am not competent at all with a 4 stroke motor some im looking for other possibilities.
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yellow gunk sounds like the fuel was starting to varnish from sitting a long time not being run---if thats the case you need to go through the entire fuel system and clean it out
Just in case you dont already know you have to remove the fuel tank to change the spark plug which is a simple task on the yfz
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My uncle had the same problem with his 06 yfz
Owner before him ran 87 octane instead of 91
Ran like crap
,cleaned the carb,changed the spark plug and put fresh 91 in and ran awesome
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I spent a few hours today with a tooth brush and break cleaner cleaning the carb it wasn't just left powderillusions mybbad for not mentioning that hopefully that's the case an I'd be a happy camper
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might check the petcock make sure its flowing--
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i know im getting some kind of flow its filling the bowl up but ill go ahead and give it a check in the morning
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K so I swapped the plug this morning there was good spark and it fired up. Blipped the throttle and she shut down so I pulled the plug and there is no more spark I bypassed the tors last night. So what ever is happening is killing the spark
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What about the rev limiter box (im clueless to what its called), but i have heard crazy issues about that. ANd i actually had an issue similiar to this with a raptor i had and i had a similiar issue and i replaced the rev limiter, and bingo.
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I'm heading to buy an ohm reader now so I can start trouble shooting
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[MENTION=85]pinned250r[/MENTION] Dave had an 05 with the timing advanced so it was similar to the dirtbike engine. It also had full exhaust and intake. That was pretty fast! Faster than B-Dogs 08 for sure.
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If the TORS is disconnected then check the TPS. Also check to make sure they didn't do any wiring themselves that may be causing problems. Check the main harness where it runs over the frame on the left side, sitting on bike, just behind the headlight. This is a known wear spot and wires get shorted to the frame. As for the carb/engine I would do the cam mod, 45 pilot, 165-175 main, 2.5 turns out on the air/fuel screw, NCVQ needle, 35-40 leak jet and adjust the ACC pump cam screw so it just touches the cam with the carb at WOT, must be off the engine to do this and remove the air box lid.
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^^^ this. i have worked on a couple that was doing the exact same thing when the TORS was acting up. you can just bypass that, or it could be your TPS also.
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i found it, last owner broke a plug and just tried to jam it together instead of fixing it. ive already bypassed the tors, got the cam mod done, checked valve clearances. Jetting is at a 45 pilot 178 main and something like a 90 leak jet. air screw is 1.5 turns out air box is gone entirely and she is just hanging out tell my new accelerator pump diaphragm gets here.
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its a 50 leak jet...thats stock. try a 35 or 40 it will work really well for you. I got a stock 04 engine that is a holeshot deamon! LOL