2009 YZ450F Won't Start, Timing Issue? Please help!

[SoCalRider84]

Thank you in advance for reading this and any suggestions you may have. I've been riding and working on two strokes for 15 years and decided to give 4 strokes a try. I bought a 2009 yz450f with a blown top end and have rebuilt the engine but cannot get the bike to start. I will describe what I have done and the symptoms below. 

 

I split the cases and went through the entire motor, checking specs, cleaning and lubing and re-torquing everything. For the top end I bought a new OEM cylinder, piston, rings, bearings, gaskets, timing chain, tensioner and guides. I bought a used OEM head with valves from a friends whose bike ran great and sold the head because he put on a GYTR head. I disassembled the head and measured the specs on the valves and springs, all were in spec and were put back in. I used the cams from the blown head as they appeared to be in better shape. I have checked and rechecked all of the valve clearances, all intake are 0.13mm - 0.14mm and exhaust 0.22-0.23mm, I also disassembled the carb, sprayed cleaner through all passages and replace all jets with oem sizes. Bike is all stock with a new air filter and spark plug (I've tried multiple plugs). 

 

When I attempt to start the bike the engine feels "tight" (too much compression?) when I kick it. If I remove the plug everything moves smoothly as would be expected. I've kicked the bike hundreds of times, primarily following the manual guidelines (no throttle, choke on, gas on) but have also tried every conceivable combination of throttle, pet-cock, choke and hot start. Out of those hundreds of kicks it has backfired 3 times. I also tried to bump start it three times, the first two it attempted to run(1-2 seconds) and immediately shut off, the third time it did nothing. I have pulled the spark plug and I am getting a good crisp blue spark each time I kick. The plug is also appropriately wet and hence I believe the issue is not in the carb. At one point I even put a water bottle cap full of gas in the cylinder and tried kicking it, no difference. I have also checked that the flywheel is properly keyed and that TDC is actually TDC using a straw.

 

I've read dozens of posts on the forum about this and related problems, it sounds like a timing issue but all my marks are almost perfectly aligned and I have "13 pins" between the "12 oclock" cam punches. Before I move them 1 tooth in either direction to see what happens I wanted to get so input from you guys. It sounds like I have the cams advanced 1 tooth from reading forums but I don't know which direction that actually is? I have attached pictures of my current timing; any help would be appreciated greatly!

 

 

[grayracer513]

Pull the plug and verify that the mark on the flywheel is at TDC. You may have dislodged the flywheel Woodruff key when you assembled it.

[SoCalRider84]

Pull the plug and verify that the mark on the flywheel is at TDC. You may have dislodged the flywheel Woodruff key when you assembled it.

Thank you for your feedback, your comments have helped me numerous times on various projects and I appreciate all the time you spend helping others such as myself!

 

I have checked and the woodruff key is in the proper location and the mark on the flywheel is indeed TDC, as determined by using a straw in the spark plug hole while rotating the crank to find true TDC. Any other ideas on what could cause this (possibly unrelated to timing that I haven't come across yet)? Is it possible the timing marks are punched that far off? Would I risk damaging the piston/valves to move it one tooth in either direction and see what happens?

[grayracer513]

The timing looks fine.  What made me suspicious was the "too much compression" remark.  That can be the result of advanced exhaust cam timing, but if your TDC mark is correct, that's not the case.  The lobe positions relative to the marks are also normal.

 

If you have good hot spark, I'd be looking at the carb again.  You may have an obstructed passageway up beyond the pilot jet.  Be certain that your pilot fuel trim screw is at about two turns out to begin with.

[SoCalRider84]

The timing looks fine.  What made me suspicious was the "too much compression" remark.  That can be the result of advanced exhaust cam timing, but if your TDC mark is correct, that's not the case.  The lobe positions relative to the marks are also normal.

 

If you have good hot spark, I'd be looking at the carb again.  You may have an obstructed passageway up beyond the pilot jet.  Be certain that your pilot fuel trim screw is at about two turns out to begin with

Today I tried a couple hundred more times to start the bike. Before I tried kicking it again I pulled the carb out and this time I sprayed carb cleaner through the jets with them in place in the carb to ensure no blocked passage ways. I also bought an easy adjust pilot screw and put that on. I have tired every combination from 1 turn out to 3 turns out on the pilot screw, all with no change. Is there a way to determine if the pilot circuit is operating correctly installed on the bike? how wet should the plug be when you pull it out after trying to start? Any tips or tricks to testing a carb to ensure it is "close enough" to get the bike running and then tune it from there. After kicking a few hundred more times I believe the "too much compression" comment was really just it gets hard to kick when you start close to TDC, if I start just after TDC or on the bottom it kicks easily so I do think its a carb issue but don't know what to do about it. Also, can you test spark quality or if I have a nice blue spark is that evidence enough? BTW, I also tried bump starting another 10 times, each time with the pilot screw slightly different, and in each case the bike starts but only for a second or less. If I do nothing in that second it dies and if I blip the throttle (light or full) it dies. Is it possible I just need a bigger hill to get it started so I can tune the carb?

[SoCalRider84]

One last question I was unclear on while rebuilding the carb if anyone can help me understand. It says in the manual to adjust the slide on the carb such that the opening is 1.25mm. I found a 1.25mm dowel in my garage, slid that under, and then adjusted the idle screw until it touched. I noticed that this was basically the end of the downward adjustment for the idle screw, is this normal? Did I misunderstand and need to have that opened more to get the bike started and idleing? 

[Bass Mechanic]

based on everything youve said the thing that has my curiosity is why the plug is wet, thats a sign your flooding the engine and why the compression seems high. either your spark is not proper or your jetting is causing it to flood. the simple solution seems to try a new plug. ive seen fouled plugs still spark when out of the engine but fail to light the mixture. when a plug fires in the compressed cylinder it takes more energy to create the heat necessary to light it off.

a funny story.. once i was riding with a friend on a trail, he had an older bike. the bike wouldn't start unless the plug wire was disconnected and held at a distance of about 1/8 inch from the tip of the plug. every time we held it there to check spark it fired right up.

we ended up using a twig from a nearby tree, wedging it in between the cooling fins of the head and wrapping the plug wire with electrical tape to the twig to hold it in that position. bike got him all the way out of the woods that day with no problem.

to this day i still cannot understand why this plug worked that way. only thing i can think of is that somehow it had some internal resistance and when directly connected the coil couldn't light it because the plug was shorted internally. with the air gap the voltage was high enough to cause some kind of spark inside. (in addition to he spark outside)

a spark plug seems cheap enough and since you've rebuilt everything else why not try one?

everything leads to the plug, even a very rich mixture will run initially when cold.. and your plug is wet..

so unless its water on your plug you should be getting a bang out of it.

[SoCalRider84]

based on everything youve said the thing that has my curiosity is why the plug is wet, thats a sign your flooding the engine and why the compression seems high. either your spark is not proper or your jetting is causing it to flood. the simple solution seems to try a new plug. ive seen fouled plugs still spark when out of the engine but fail to light the mixture. when a plug fires in the compressed cylinder it takes more energy to create the heat necessary to light it off.

a funny story.. once i was riding with a friend on a trail, he had an older bike. the bike wouldn't start unless the plug wire was disconnected and held at a distance of about 1/8 inch from the tip of the plug. every time we held it there to check spark it fired right up.

we ended up using a twig from a nearby tree, wedging it in between the cooling fins of the head and wrapping the plug wire with electrical tape to the twig to hold it in that position. bike got him all the way out of the woods that day with no problem.

to this day i still cannot understand why this plug worked that way. only thing i can think of is that somehow it had some internal resistance and when directly connected the coil couldn't light it because the plug was shorted internally. with the air gap the voltage was high enough to cause some kind of spark inside. (in addition to he spark outside)

a spark plug seems cheap enough and since you've rebuilt everything else why not try one?

everything leads to the plug, even a very rich mixture will run initially when cold.. and your plug is wet..

so unless its water on your plug you should be getting a bang out of it.

Thank you for your input. I do believe it is my jetting causing the issue but cannot figure out if its too lean or too rich. I have tried 3 plugs, first a new NKG C8ES then a new NKG C8EI (the iriduim one, I think thats the part number) and the old NKG C8ES that came from the used head I'm using. I have checked the spark plug gap and it is correct and I have also check the plug caps resistance and its in spec.

 

I guess I'm using the term "wet" liberally, the plug is not dripping or anything when I remove it, just has a fuel residue on it I would assoicate as being the proper amount of fuel if it were a two stroke (I don't know what a four strokes plug should look like, this is all new to me). Today I took out the pilot and replaced it with a 48 (was stock, 45), still no luck but seems "closer". My biggest question is where is the slide supposed to be to get in the ballpark and get the bike started (or does this have no bearing)? Is the 1.25mm gap in the manual correct or am I misintrepreting? I know the affects idle and the bike will start when bump starting but dies instantly choke in or out.

[grayracer513]

Idf you can bump start it, keep it running by hand and turn the idle speed up until it will actually idle.  Warm it up, adjust the pilot screw, and set the desired idle speed.  It should kick start much more easily after that.

 

The 1.25 mm slide positioning is for timing the accelerator pump, not a base idle. 

[SoCalRider84]

Idf you can bump start it, keep it running by hand and turn the idle speed up until it will actually idle.  Warm it up, adjust the pilot screw, and set the desired idle speed.  It should kick start much more easily after that.

 

The 1.25 mm slide positioning is for timing the accelerator pump, not a base idle. 

When I bump start it it only runs for 1-2 seconds no matter what I do so I don't have a chance to adjust anything. Once I've timed the AP, is there a base idle you can recommend to get me in the ballpark? I'm currently using a 48 pilot jet at 1.5 turns out on the pilot screw if that helps.

[Bass Mechanic]

When I bump start it it only runs for 1-2 seconds no matter what I do so I don't have a chance to adjust anything. Once I've timed the AP, is there a base idle you can recommend to get me in the ballpark? I'm currently using a 48 pilot jet at 1.5 turns out on the pilot screw if that helps.

Once you get it running the idle mixture is not all that critical. You should be able to open the throttle and keep it running. If it won't idle you can mess with the idle speed and mixture.

I just fixed a Ktm that had a similar issue and all I did was clean out the idle circuit. Now it runs fine.

If you have a little carb cleaner you can try spraying a few shots in the air intake by removing the filter. If it fires right up on carb cleaner then you know your jetting or carb is the culprit

[grayracer513]

It really does still sound like a pilot circuit issue.  When you spayed carb cleaner through things, did you find that when you sprayed through the pilot jet seat that the spray came up into the carb throat just on the engine side of the slide?

 

Bear in mind that the pilot jet itself may be partially clogged.  The metering orifice is only .017" , and if a film of varnish no thicker than .001" dries in there, it makes the jet work like it was a number 32 instead.  Read this:

 

https://www.thumpertalk.com/topic/681801-bike-wont-start-dont-know-what-to-do/#entry6879695

 

The problem may also be:

 

• Clogged air jets
• Damaged or missing O-ring on pilot screw
• Damaged or missing seal on hot start plunger
• Hot start stuck open or no free play in cable/cable out of place
• Slide vacuum release plate upside down/cracked/chipped

[RMK800]

Have you changed the fuel screw at all? I've seen an issue where a buddy changed his file screw and messed it up by the missing parts. Make sure all the parts are there with the fuel screw.

[SoCalRider84]

 

It really does still sound like a pilot circuit issue.  Wen you spayed carb cleaner through things, did you find that when you sprayed through the pilot jet seat that the spray came up into the carb throat just on the engine side of the slide?

 

Bear in mind that the pilot jet itself may be partially clogged.  The metering orifice is only .017" , and if a film of varnish no thicker than .001" dries in there, it makes the jet work like it was a number 32 instead.  Read this:

 

https://www.thumpertalk.com/topic/681801-bike-wont-start-dont-know-what-to-do/#entry6879695

 

The problem may also be:

 

• Clogged air jets
• Damaged or missing O-ring on pilot screw
• Damaged or missing seal on hot start plunger
• Hot start stuck open or no free play in cable/cable out of place
• Slide vacuum release plate upside down/cracked/chipped

 

When I spray carb cleaner through the pilot jet orfice it comes out the pilot screw (primarily) and pilot air holes (just a little). If I spray throught the pilot screw hole it is a nice jet only on the enigne side of the slide with just a little (5% or less) out the pilot fuel and air jet orfices. The pilot screw definatly has the oring, spring and washer in the correct place and I've tried 2 different sets of parts. I did notice the seal on the vacuum release plate is "wavy" and swollen, looks like I got carb cleaner on it so I'm ordering a new one. All of the jets with the exception of the needle are new (including both the 45 and 48 pilots I've tried). In addition to the seal I'm ordering, I'm going to buy a carb rebuild kit and try one last time.

 

If that doesn't work my buddy has an 07 YZ450f, also all stock and runs excellent. Any issues with me putting his carb on? I believe they are the same thing? (I haven't done this already becuase he's on vacation until the middle of the month)

[grayracer513]

It should drop right in place and work.  There may be some minor differences in idle trim because of the cam differences between the two, but not much.

[grayracer513]

If you let the seal sit overnight, it will usually return to its original size and shape, then you can reuse it without difficulty. 

[04 wr450]

You seem to be going through process of elimination ok. I would get a timing light and get someone to kick bike over with plug out ,while you see if it is actually firing a spark at the right time.had a bike once that refused to start.after checking ignition timing we found it was advanced.replaced c.d.i and instantly fixed it.also make sure exhaust system is not blocked! Just a couple of ideas to help.

[SoCalRider84]

Thank you everyone for your suggestions. I have still not been able to get the bike running (I was on vacation and just got back to it yesterday).

 

I have again rebuilt the carb with another new kit and all new jets (all stock sizes, 45 pilot and 2.25 turns out on the pilot, I have also previously tried a new 48 pilot). After I reassembled everything I can now start the bike but only if I hold the throttle at ~1/3 open. The bike starts within 2-3 kicks everytime with the throttle open and choke on but dies within 3-5 seconds as I try to feather the throttle and adjust the idle. Obviously the bike is not getting enough fuel through the pilot circuit to start without the throttle but I don't know why. I have sprayed carb cleaner through every orfice and nothing is clogged.

 

Could the float level cause inadequate fuel pickup from the bowl? No fuel leaks out when kicking it so I know the level isn't too high but possibily too low? I set it to 8mm from the carb surface to the lowest part of the float at the point where the needle valve just starts to move in its bore (when holding the carb upside down and rotating as the manual suggests). When I hold the carb upright and blow into the fuel inlet while operating the float this corresponds to fuel shutoff approximately 15 degrees past horizontal (15 deg further into the carb body). Does this sound about right? Lastly where should the idle adjustment screw be approximately? I currently have it set 2 turns in from the point it just touches the pivot that connects to the throttle cables.

[SoCalRider84]

I know its been a while but I realize I never followed up to close this out. Thank you to everyone who gave their suggestions.

I never figured out what was causing the problem but did get the bike running. After trying everything I could think of I took the head off my friends 07 and put it on my 09, it fired right up. I then put my 09 head on his 07, to my surprise it too fired right up. I put both bikes back together with their respective parts and they both ran perfect. I'll die never knowing what was wrong but at least they run!