All Good Mechanics, Please Read And Help!!!

[raptor_02]

I have a 2004 YFZ450. It has a full Big Gun race exhaust, 172 main jet, 45 or 48 pilot. (The biggest pilot jet in the GYTR JET KIT). My exhaust cam is retarded 1 tooth. Well a about a month ago I posted on here about my quad cutting out every now and then. I could ride it for days and it wouldn't do it then it would start doing it again. We went through the carb, cleaned the tank, checked the little screen and all the jets and also changed the plug , new gas and etc. Quit for a day then it started doing it again. Well over the month I have noticed a few tendacies the quad is having. It mostly does this when I am mx riding. When I land hard off jumps or just hammering through whoops or whatever is when it does it. To me it's like it won't hardly take fuel or something. It will start up , idle but then when I apply the throttle it kind of dies. But this past weekend it done it as I was going to the gate right before my race. I let it idle and kept revving it up and it got lined out before the race and I thought it would be fine. Makes you think it is bad gas or something but a person don't get bad gas as many times in a row as me. But during the race it started to do it, i got it lined back out but during the race it quit and died and cost me 2nd place. Please good mechanics, give me all possible solutions. We are going to go through the whole carb and all the electrical stuff on the quad including CDI box and stuff. Any suggestions would be greatly appreciated

[Quad18star]

My buddy had the same thing happen to his bike . I'll try and get a hold of him later on today and ask him what the problem was . But I know he was having the exact same problem as you are having right now .

[xc400ex]

Jetted to rich, put in a 165 and it will run great, its ok to run them a litttle lean.

[crayfz]

Originally posted by xc400ex
Jetted to rich, put in a 165 and it will run great, its ok to run them a litttle lean.
I agree, been there done that.

[Mobile Dyno]

Check your electrical system. A guy at an event had the same problem. He didn't exactly know what it was that was causing it but he thought it was the stator. He checked and cleaned everything also. He was :mad: I heard they have had electrical Problems. We dynoed another yfz and we had to run it with the headlights on because of a similar prob. Thats how he was riding it. We turn the lights off and it would cut out. :confused: It looked like a banshee or blaster does with the lights on ,Fades in and out. There was something going on. If I find out more I'll put it on here.

[raptor_02]

come on guys, help me out here??!!!!!??!!

[400grl]

Post this on another YFZ only website and you might get more help.........

Sounds electrical........

[Splatter Matter]

you should check you stator and rectifier they are the main thing that go bad. and will give you the problem you stated

[jlhughes750]

Haaaaaahaaaaaa!!!!!!!!!!!


This may sound like the stupidest thing ever..................but I can almost guarantee this is your problem!!!!!!!!!!!!!!

Next time the bike does this, stop pull off the tank and plug your cap back onto the top of the spark plug!!!:eek:

I have heard the same problem from nearly everyone I know that race the YFZ through some real rough terrain or lotsa jumps on a MX course!!! I took a rubber from the rear portion of a 250R frt. fender and glued it to the top of the coil!!!! Now my IMS tank, and the rubber bumper, hold the cap on while I'm riding!!!!!!

The vibration alone will make it cut out while sittin still and revving the motor!!!

Hope this helps !!!

later, J

[daddio]

my kid's yfz had the same problem. It turned out to be a wire near a shock tower had rubbed thru the insulation, and was shorting out, sometimes.

Originally posted by jlhughes750
Haaaaaahaaaaaa!!!!!!!!!!!


This may sound like the stupidest thing ever..................but I can almost guarantee this is your problem!!!!!!!!!!!!!!

Next time the bike does this, stop pull off the tank and plug your cap back onto the top of the spark plug!!!:eek:

I have heard the same problem from nearly everyone I know that race the YFZ through some real rough terrain or lotsa jumps on a MX course!!! I took a rubber from the rear portion of a 250R frt. fender and glued it to the top of the coil!!!! Now my IMS tank, and the rubber bumper, hold the cap on while I'm riding!!!!!!

The vibration alone will make it cut out while sittin still and revving the motor!!!

Hope this helps !!!

later, J


happened to me also! Make sur it clicks all the way down on the plug.

[Splatter Matter]

Originally posted by sinister450
happened to me also! Make sur it clicks all the way down on the plug.


yea if not this is what will put out of a race. look at the top of the plug it melted off.


http://www.imagestation.com/picture/sraid148/p6166084b0f3a9eba2f674d685a306e5c/f6115b7c.jpg

[daddio]

Originally posted by Splatter Matter
yea if not this is what will put out of a race. look at the top of the plug it melted off.


http://www.imagestation.com/picture/sraid148/p6166084b0f3a9eba2f674d685a306e5c/f6115b7c.jpg

that is what happens when the cap is worn out or is not on all the way. the top of the plug "arcs" and melts. this happened to my banshee.

[4TraxRider]

Mine was doing that also adn was told it was my Pro-design kill switch. It's run fine with the new gunnar I put on, but I didn't really understand why.

[raptor_02]

guys are sure do appreciate the help. Hey JLHUGES, my dad said something about having to push down the spark plug cap like you mentioned. I bet that might be the problem But we will do some testing and make sure. If anyone else has anymore ideas of what it might be please post them but i think JLHUGES figured it out for me. Dude if your right I about this I can't thank you enough man cause this has been agravating me for months now. I'll post and let you all know if that's the problem.

[jlhughes750]

NO Problem!!!!!!!!!;)


I put 21 Harescrambles (1.5 hours each) on the YFZ plus the 6 hours of Rausch and 2 GNCC's!!! not to mention all the riding and practicing!!!!! I had this problem early in the year, but never during the race!! I DNF'd one race due to a broken frt. sprocket, and had the battery die, only once all year!!! When the battery died I had 3 races on the bike with out using the lights....all other 18 races I raced with the lights on!!!!!!

I guess I'll knock on wood, but I have had great luck with the YFZ!!!! Gotter all torn down now, goin to see Pappy soon!!!!

[raptor_02]

turns out that that was not the problem. Man this sucks. Were going to go inside the whole carb and check all the electrical stuff and hopefully we will find it. If we find no problems I guess it would have to be the CDI box. Could someone explain to me about the TPS (throttle position sensor) and how that works.

[daddio]

the "tps" senses the position of the throttle and adjusts the advance/retard of the ignition.
I have heard of people having problems with the performance of their bike, because they "broke" or "cracked" the sensor while changing jets in the carb. I feel it's real easy to damage this unit, because it can hit the frame when you "trist" the carb to access the float bowl from the left side.
my 2 cents.