MrYfz
A Class
My YFZ and I love to fly high
Posts: 241
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Post by MrYfz on Jul 28, 2007 18:55:55 GMT -6
Okay, heres the deal. Took the head in to Jackson to check the valves. All looked good other than shims.  Put it back together and it now starts but wont hold an idol, and back fires really bad.  Checked coil, stator, throttle positioning sensor, cdi box, rechecked timing marks, and cleaned carb. Running out of ideas, and becoming very flustered as never came across something I couldn't figure out.  Don't get me wrong here I'm not a mechanic, but I can usually figure out whats wrong then decide if I can fix it or if she goes to a shop. Any ideas or known similar situations out there? I'm in MISERY without my baby! |
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Post by grizzly660 on Jul 29, 2007 16:16:00 GMT -6
Check spark plug or the plug wire could be broke inside,and clean all contacts............
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xman
Seasoned Pro
Push it to the X-treme!
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Post by xman on Jul 29, 2007 23:14:27 GMT -6
When you cleaned the carb did you take it apart and clean it or just spray cleaner through it. When I rebuilt my 350X it did something very similar after I got it put back together. I thought it was timing related and ended up taking the rocker cover back off and readjusting my cam and reset the timing.
Turned out when I had taken the carb apart to give it a good cleaning a needle jet had fallen out and I didnt notice. Needless to say it ran like crap and once I reassembled the carb with all parts present she ran perfect.
Its not likely you have the same problem, but if you tore into the carb at all I'd double check that everything is good. Or something could be stuck in it too. Just some thoughts from my personal experiences. Hope you figure it out, I can sympathize how you're feeling!
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Post by Weck on Jul 30, 2007 6:51:13 GMT -6
The "won't idle and backfire" issue may be caused from being very lean.
Like Xman said can you give us some details on how you cleaned the carb. If this thing took a big shot of water to start this problem originally maybe the pilot jet is plugged. The idle mixture screw and how far it is turned in or out determines how much gas the pilot jet will flow. The easiest thing to do is make sure the idle mixture screw is at least 2 turns out and in your case I would say 2.5 turns out from fully seated.
Then make sure the floats in the bowl are not stuck up or down.
Stupid question but is the air filter clean or even on. Water will turn filter oil to slimey gunk. Here is another dumb one that has bit me twice. Make sure the air vent on the gas cap flows freely. Take the cap off and start it. Any difference.
I'll think about this a lil more and see if anything else comes to mind.
Start a post or search the posts on bluetraxx.com and / or yfzcentral.com
I'm no pro either but could stop by if needed.
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MrYfz
A Class
My YFZ and I love to fly high
Posts: 241
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Post by MrYfz on Jul 30, 2007 7:44:48 GMT -6
Ah the carb.  We have opened it twice now as we are all seeming to think the same thing. We have cleaned every passage, every diaphragm, every jet and checked float ability. Today it will go back in. Last night me and my buddy went back through all the connections and made sure everything was testing correctly again, and made sure all connections were solid. Before we tore the crab back out we did get it to idle but it still back fired and would shut down for no reason. Oh yes and Weck I did check the gas cap. As this has gotten me in the past also. Did that one piss you off as much as it did me as it seemed to be the very last thing you think of? Now it seems to be the very first thing to think of. |
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ubnpast
Seasoned Pro
Board Member
Posts: 1,473
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Post by ubnpast on Jul 30, 2007 8:45:37 GMT -6
It sounds like a symptom of a throttle override sensor. I have been stumped because of one of those before. I remember being stumped working on a Blaster because the sensor on the emergency brake was tripped.
Just a suggestion, as I dont know if the YFZ has anything like that, but most all Yamahas seems to be notorious for those switches.
Possibly along the lines of it being lean like Weck said, is there any air leaks between the carb and the cylinder?
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Post by Weck on Jul 30, 2007 8:58:20 GMT -6
/\ He's right there are probably two electrical switches or empty plugs that used to go to those switches that could be checked. You said you went over all the connections so you probably already touched on this. Based on a Raptor which I would assume would be similar, I think there are two switches in the stock clutch perch assembly. If either of these are activated it will act like a very low rpm rev limiter. I think both are normally open connections which means the two wires can not be touching each other or frame metal. I am assuming you run an aftermarket clutch perch so these are probably taped up and tucked underneath the front plastic.
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Post by Weck on Jul 30, 2007 9:13:57 GMT -6
Found this on Bluetraxx \/ www.bluetraxx.com/phpBB/viewtopic.php?t=74713&highlight=backfireDo you have a volt meter. Maybe measure the battery voltage with the motor off and it should about 12v. With the motor running it should be a little over 14. I wonder what the volts would do if you increase the RPM. That thread talks about the voltage regulator being the problem. You probably know this but the regulator is that thing mounted to the front of the frame with cooling fins on it. |
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Post by Weck on Jul 30, 2007 9:32:01 GMT -6
Maybe its the tootsie roll on the seat...   |
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ubnpast
Seasoned Pro
Board Member
Posts: 1,473
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Post by ubnpast on Jul 30, 2007 15:22:02 GMT -6
^ Weck is just jealous of that picture because he can't make it over tree roots that size. ....ps We did wait until MrYFZ got a lot of good info before we started teasing anybody on his thread. |
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MrYfz
A Class
My YFZ and I love to fly high
Posts: 241
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Post by MrYfz on Jul 30, 2007 20:02:09 GMT -6
Maybe its the tootsie roll on the seat... Not sure why your looking at my tootsie roll , but don't be jealous.  Oh yeah did I mention SHE'S ALIVE!! ;D Apparently there were multiple problems. Here goes 1. valve shims 2.poor spark plug boot to spark plug connection 3. filthy carburetor 4.poor connection at the pickup coil plug 5.This is the one that really got me, there is a bad wire were the pickup coil and the magneto come out of the crankcase. I twas the darnedest thing, when Id check the pickup coil ohms like the book said it read fine, but apparently when ever id hook it back up depending on how it was moved it would run then it would vibrate for a minute and wallah shut down.opened the taping it the case and found nothing. However every step actually got the d**n thing running better and better. So in many ways you were all right and I appreciate all the advice. X, thanks for the check the carb again advice, That's the same idea my Buddy had and he tore it alot more apart than I thought you would ever have to, and boy it was filthy. |
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Wait4me
Seasoned Pro
Memories....
Posts: 1,387
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Post by Wait4me on Jul 30, 2007 21:03:25 GMT -6
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Post by Weck on Jul 31, 2007 7:20:58 GMT -6
I bet it starts and idles a lot better now too.
You gotta PM.
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xman
Seasoned Pro
Push it to the X-treme!
Posts: 1,272
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Post by xman on Jul 31, 2007 14:18:50 GMT -6
Glad to hear she's back!  It's amazing how many itty bitty parts are in those carbs, and how even a little speck can really reak havok. Guess this solves the question of how many guys help does it take to get a Yamaha YFZ450 running!  |
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Post by grizzly660 on Aug 1, 2007 19:29:36 GMT -6
;D After talking to him by phone , the wire coming out of case ,you wiggle it it quits running . Sounds like the wire coming out is broken or lose connection in the magneto housing.
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Put it back together and it now starts but wont hold an idol, and back fires really bad. 
Don't get me wrong here I'm not a mechanic, but I can usually figure out whats wrong then decide if I can fix it or if she goes to a shop.
We have opened it twice now as we are all seeming to think the same thing. We have cleaned every passage, every diaphragm, every jet and checked float ability. Today it will go back in. Last night me and my buddy went back through all the connections and made sure everything was testing correctly again, and made sure all connections were solid. Before we tore the crab back out we did get it to idle but it still back fired and would shut down for no reason. 
