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Discussion Starter · #1 ·
Hi all,
I'm having an issue with 2010 yfzx and I'm not sure where to start. Heres the story. Traded for the bike used back in June. It had a wiseco shelf piston, wiseco intake cam, hmf slip on, and msd. I wasn't happy with the tune and how it ran. I race GNCC so I opted out of the msd and bought a vortex. That fixed a lot of my early issues. It apparantly had a better tune and all was fine. Ran a few races and swapped the wiseco cam out for the 08 yz which suited my riding style better. All was perfect. The week before the St. Clairsville race I went to a certain former 9x champ's mechanic for a weekend to do some test and tune on suspension. That's the first time it acted up when I got to really revving the bike out it wanted to stutter and miss kinda like the timing was being pulled or something. He told me it was probably my Vortex went bad that I need to replace it. I was slightly apprehensive about dropping that cash again not knowing for sure so I took it home and cleaned up the ecu connections, fresh dielectric grease and hooked it back up. Seemed to work fine at home, but honestly I live in town and have no room to really open it up. At St. Clairsville immediately upon the holeshot it starts missing in the upper rpms. It was a mud fest so I would short shift and keep it somewhere below probably 8000rpms and it ran fine. Sometimes I would rev it out though and it wouldn't have the miss. Then sometimes it would. Regardless a new problem came about. I would be hammering down a trail and all of a sudden it would just die like fuel was cut to it. That happened 4 or 5 times in three laps until it finally stranded me and would start back. I assumed electrical but upon inspection I found it wouldn't start back because the starter brushes had grenaded. Explained the no start, but still not why it died. I replaced starter and went for a ride. Ran flawlessly. The week before Ironman I wanted to freshen the engine up. I had put a lot of hours on the top end and had a new gytr piston sitting here from a deal I made. I am in the process of building a second bike for next year so this machine will now be my Mid South winter and practice bike so I wasn't concerned about every drop of hp. I took it apart to find a nasty little crack in the nickasil and dropped a fresh cylinder on it. Now I had a spare head that I had did an epoxy part on after studying the old mixxer porting thread. This was my first port and I thought it honestly came out pretty good. I resurfaced the valve seats and everything looked good so I decided I would drop this head on and see how my work did. I assemble everything. Fires up first try and idles beautifully. Revs out clean. I shut it off and think it's good. It rained all week at my place leading to ironman so I never go to try it out until I went to load it up. Pulled it out started up fine. Idled great. Went for a spin around the yard. Revved good. Pulled good. I was happy. Turned around to start toward the trailer, touched the throttle and it died. Absolutely did not want to start back. I push it back to to the shop and start checking over things. Found nothing. Went ahead and loaded my other equipment up and bike cooled off. Went again and started perfectly. Run great again....until it warmed up. Then it died. Cooled off again and started it and rolled it into the trailer thinking I'll get some other opinions at the track and loaded up my spare head and gaskets and stuff like that. At this point I'm still thinking electrical. In the back of my mind I did question my head, but figured if I had an issue with the head it would start sometimes. It would idle cleanly, and it sure wouldn't pull great under a load. I get to the track and won't start. Someone tells me to pull the ecu connector apart and check all the pins inside that one hasn't slid back some. One pin was slightly further back. I push it back forward and secure it. Assemble and bam it starts. Warms up, runs fine. I ripped it up and down a field for about 30 minutes no problems. I went back to my pits and made some minor suspension adjustments. Bike cooled off. Later on I wanted to take it up to a friend of mine in pro pits who had the vortex software and just let him take a look and see if he could nail down any problems with that. Started fine rode to his trailer. Shut if off by the key to talk to him. He tells me to push it under his tent hooks computer up and says start it. That was the end of it. It never would start back. We checked ecu connector again, looked fine. Checked valves, looked fine, double checked timing, looked fine. We messed with it for an hour or two and finally gave up nearing dark. Towed it back to my pits. The next morning it's race day I go to try and start it. No go. Cranked it until the battery was too weak. Chalked it up and decided I was spectating. Never touched it again until I got home pushed it out of the trailer and into the garage. Let it set for a week. I sold the shocks off of it so it's been sitting there unsuspended for a couple weeks until my new ones come in, but for kicks I decided to hit the starter the other day. With a very weak battery it makes about 2 sluggish rotations and fires and sits and idles perfectly again. I have no clue where to start with this thing. I was told to throw a new harness on it, which sounds practical but with harnesses in the $400 range I hate to just throw one at it not knowing if that's the issue. I still think about the head in the back of my mind, but I think if something was bad wrong there it would never run right. Then could it really be that ECU doing that. Or could it be something I haven't even checked yet like I thought about the possibility of the stepper motor sticking that might cause then condition. Shocks will be here today so I'll be able to start testing on it, but I wanted to get some opinions on just where on earth to start. Maybe someone had an issue like this before. Sorry for the very long read, but felt like it was important to have all the background info. Thanks guys.
 

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Discussion Starter · #2 ·
Has anyone ever had a Vortex go bad?
 

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I by no means am a mechanic, and i don't know a whole lot either but just trying to help out and spit ball ideas. I would try to check the fuel pump....had a kfx450 last summer and had similar problems! ran fine on the bottom end, then get into the higher rmps and it would just stutter like yours. I took it get the valves and everything checked, turned out the plating in my cylinder was chipped so got a new cylinder and threw new rings in sure that the problem would be solved. Ran it and still stuttered on top end, i was dumbfounded. I had no idea what it could be. Just guessing i ordered a new coil thinking it was maybe going bad, and it still didn't fix it. I took it to a shop and they said the fuel pressure was a little low but not bad, they honestly said "we don't know whats wrong with it, i would just get rid of it". i was about to sell it, but my buddy found a guy that had some parts laying around and had a good fuel pump he would sell. I got the fuel pump for $50 bucks and installed it. quad ran perfectly fine after that! so it turned out it was the fuel pump after all. Kind of similar to your symptoms so just thought id throw you my 2 cents. good luck man!
 

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In the years I have had this thing, I have had those symptoms caused by something different each time. I had a wiring harness ground at the front against the frame by the radiator. Then I had a wire break at the Idle air Control valve and would die and not start. Pissed me off cause neither issue would throw a trouble code. I bought a harness on ebay for $100 and tore it apart and took out the wires that I don't use like the on off switch, clutch switch, and the lights. I wrapped it with an abrasion resistant tape and has not been a issue the past few years. The most recent reason I have had this issue is due to the battery connection. It would bog and die and not start and that's all I would have to do is tighten the connection and it would be fine till it worked its way loose again. I also changed that so that problem is gone too. I always wondered why chad wienen's list of mods included upgraded battery leads.
 
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