I have done a lot of reading, research, trouble shooting, and work before I posted this. I apologize for how long this post is, but wanted to include all the details of what I've done to keep the thread in the right direction.
So, I am having issues with my bike, and have done a ton of trouble shooting. Let me start of by saying I have checked my timing about 13 times, and have three other people verify it as well….I don’t think timing is an issue. I’ve also disconnected the kill switch. I’ve also rebuilt 4 top ends on various YZ250Fs in the past, however this is my first FI bike.
My Bike: 2014 YZ250F GYTR head, FMF Ti Exhaust, 51 hours. Primarily ride track and race C Class (8-10 events per year).
Work performed this time on the bike: Timing chain, a new 2015 stock piston, wrist pin, rings, and wristpin oil spray. Verify valve clearance after install, and rotation. I checked the cylinder, piston, rings, for clearance and tolerances. I checked the crank for tolerance as well. The piston has the F mark towards the front of the bike (which correlates with the intake valves, larger sized)
(NO SPARK ISSUE):
I put the bike back together and it would not start, no sputter, no burp, nothing. I diagnosed it as a no spark. I checked the timing and valve clearance (its dead on, and yes I know the exhaust valves go towards the rear of the bike), I checked the chain tension as well. I was trying to ground the plug to the valve screw and or the frame. I Disconnected and inspected all connections off the wiring harness, and checked for any fraying especially up around the radiators/frame area (all looked good). I followed the manual checking resistance on the kill switch, primary and secondary coil, spark plug cap, crankshaft position sensor, stator, checked ground, spark plug resistance and gap (also a new spark plug). I made sure the ECU was in the upright position. However, I was a retard and measured the secondary resistance of the coil including the cap…so it was 9k ohms over. I thought this was the issue, so I purchased and installed a new coil…but found this mistake after I already installed it.
I pulled the clutch in and kicked the bike and Finally got spark!! My neutral switch is directly hardwired into the harness, so I could not pull it to check resistance. And for some bizarre reason, I get spark every time with or without the clutch pulled in. So the no spark issue should be cured....I think (see last few paragraphs). (I'm only able to see the spark when the spark plug is grounded to the frame, I don’t have the tool to inspect what happens when its installed in the head.
I still am having trouble with a no start (next step CHECK FUEL SYSTEM)
With spark figured out I’m still not getting a start, a sputter, any sign of life. I checked the timing again (its dead on). I checked the woodruff key on the flywheel, and can shine a light down the keyway and see the woodruff key in the keyway. I also checked that TDC is actually the same as what is marked on the flywheel by putting a long screwdriver in the spark plug hole and rotate the motor to see its highest position. I checked the timing again (its dead on). I dug deeper into the electrical system. I checked that I get voltage spikes from the stator, rectifier, and condenser. Unfortunately, my multimeter is just a handyman’s so it doesn’t hold the peak voltage, and takes the RMA so the spikes are lower than expected. However, I do see a spike in voltage for each of the electrical components listed above. I grabbed a GYTR programmer and connected it to the bike, No trouble codes showed.
I checked the timing again (its still dead on). I continued looking into the fuel system. I set up a system to clean the injector with brake cleaner and a 9 volt battery, spraying cleaner into the fuel nipple and pulsing the injector. It sprays a large good mist, and did from the first spray. I then pulled the tank and connected the 9 volt battery to the fuel pump and can hear it spin. Checked the TPS with the GYTR programmer and shows no errors (throttle 5 deg at 0 and 88 deg at open I know I can adjust this better, but should not be a no start issue).
I kicked 150 or so times. Variation of throttle open, closed, mid, Cold start open, closed….nothing. I pulled the plug and the plug shows only a little wet residue on the furthest parts from the electrode. The piston has a sheen of fuel when you shine a light down. The fuel line is not pinched, and you cannot squeeze the line, which is telling me the fuel pump is working, and the injector is spraying fuel. I also disconnected the fuel to injector connection and fuel sprayed like it was under a significant amount of pressure. As I was using compressed air (about 50 psi) to blow out the residual fuel from the top off the piston, I noticed air blowing out the exhaust. I rotated the motor to TDC, checked the timing, and blew again, still a bit of leak by…..ahhh leaky valves causing leak by and not allowing spark. I verified the valve clearance and it was still right in spec.
So I pulled the head off to pull apart the valves. I found a bit of carbon buildup on the valves, and assume that during the cleaning, some of the carbon deposits were removed, and others weren’t which masked the valve clearance and sealing. Looking at my head, it needs seats to be cut and new valves. Fortunately, I know someone at Yamaha, and I had a spare GYTR head sitting in a box with 0 hours on it.....same part number as my existing one. I assembled the head, checked the valve clearance and timing. Rotated the motor lightly, and checked the timing and valve clearance again and chain tension. I kicked the motor over a few times, and checked the timing and valve clearance again. I also checked the timing chain tension, and the tensioner is doing its job. Assembled everything back together…….and still no spark…..WHAT the hell!!??!?!
Checked the spark, and I still have spark. I tried spraying starter fluid in the intake and kicking….nothing. Sprayed starter fluid in the spark plug hole and then install the spark plug, still nothing. I checked the timing again, still dead nuts on. Had two other people verify the timing. I tried bump starting it, it sounded like bump starting a 2T with a fouled plug, just bog, bog, bog, wheel lock.
Since there was absolutely no sputter, or sound of life with starter fluid, I’m thinking that it’s a electrical issue or a spark issue when the spark plug is attached to the motor. Thinking it might be a grounding issue, I pulled the ground wire off the frame (it looks as clean as the day it was installed), and reinstalled it. Still nothing. I am getting a fairly bright blue spark when grounded to the frame. I double checked the gap, and also tried a new plug....still nothing.
I am now at a loss and feel like a retard. I really want to get back and ride some moto. I have talked with Yamaha on the phone a few times, and have helped me thus far. They have been great, but I'm a stubborn engineer, and would prefer to fix this on my own.
I'm thinking the next steps are pulling the fly wheel and check the key (although I would think that verifying that TDC with the location of the mark on the fly wheel would prove this is accurate). Then replacing the Condenser, Stator, and/or ECU, then cam position sensor.
I apologize for the extra long post, and have read and searched here and Vital (yes I saw the TPS thread on the 2015 YZ250F).
Are there any other directions I should try, any other things I'm missing?…or should I give up and send it into a shop/dealer to diagnose?