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oscaroc

Struggling with timing and getting my bike started

32 posts in this topic

I have an 07 yz450f I have recently installed a new head and timing chain. I got everything back together and kicked this thing over a bazillion times and it will not fire. I've searched this site and researched all the threads. What I came up with is to check fuel, timing marks, count chain pins, make sure shims are seated and correct clearance. I've tore this thing apart 3x. I have spark, per taking the cap off and kicking it over... It sparks! I've checked timing, flywheel is lined up with the "I" the cams are line up at 3 & 9 on the gasket surface. I have 13 pins between cam 12:00 marks... Not sure how that would ever change. Can somebody give me a direction to look towards, I'm at a loss!IMG_1474738567.563341.jpgIMG_1474738594.940787.jpg

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I might add that the valve clearances are all in spec on the bigger end. The shims are all seated correctly and the carb wasn't messed with at all when I had it off and reinstalled. And new spark plug that I gapped correctly.

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Make sure your bottom end is not full of unburnt fuel mixture

 

Kick it over a dozen times with the kill button on, wot.

 

Then turn the idle way up and try and start it (using choke and no throttle)

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Thanks man, I did all that. Made sure I was getting spark again and BAM!!!! She gave in, happy bike.... Happy life! IMG_1474758494.556200.jpg

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What it sounds like you have the exact same problem I have.. a few questions. First how do you correctly gap a spark plug? Second how do you get rid of any leftover fuel in the bottom end?. And did you hold the kill button down the whole 12 times. Wot= without throttle? Thanks lol

I have the exact same bike as you to so I'm hoping this helps me. I've had this thing torn apart countless times and worked on it all day every day for the last week. I've already completely cleaned the throttle out changed the spark plug, timing looks exactly like yours. I hoping this fixes my problems

Edited by romansam

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Make sure your gapped right per the service manual. Which I believe is 0.7-0.8 mm. Use mm feeler gauges to determine where your plug is currently. While you have the plug out, I would reconnect the plug wire and kick the beast over a few times in the dark. What your looking for is a spark!!! When you pull your plug, notice if it's dry or wet with fuel.

Back to the spark, if there is no spark. Check all your connections & plugs. Make sure they are all clean, no bent pins and all are fully seated when plugged in. If you still don't have any fire, I suspect your CDI may be bad.

As for fuel in the bottom end, I'm guessing it's more fumes than actual liquid fumes. Kicking it over a Few times seemed to clear it out for me, or so it seems.

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Ok i have good spark while the spark plug is out and connected and held up to the frame. I put it back in held the cut off switch down while i kicked 15 times. Twisted the knob on the left hand side bottom of the carborator clockwise 3 360 degree times. Pulled the clutch out and kicked another whole 12 times and still nothing.. Ahhhh this bike will be the end of me.. does it sound like I attempted what you did correctly?

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Did you say that you've checked you're valve clearances already?

Two things that made my bike hard to start were a zeroed out intake valve and a wet/flooded spark plug.

I reshimmed the valve and fixed the flooding problem and now it starts reliably.

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Did you say that you've checked you're valve clearances already?

Two things that made my bike hard to start were a zeroed out intake valve and a wet/flooded spark plug.

I reshimmed the valve and fixed the flooding problem and now it starts reliably.

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[emoji106]what thumbster said, make sure your valves are set up within the clearance specs. I assumed you had done that already. That will definitely make it hard starting. My 07 250f was hard starting and after messing with the carb for a few runs I finally checked the valves and reshimmed. It started and ran great afterwards.

Are you completely sure you have fuel getting to the cylinder?

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Did you say that you've checked you're valve clearances already?

Two things that made my bike hard to start were a zeroed out intake valve and a wet/flooded spark plug.

I reshimmed the valve and fixed the flooding problem and now it starts reliably.

Ok how did you fix the flooding? I think that's my problem. I can get it to start only after tipping my bike over getting all fuel out and trying to start it

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[emoji106]what thumbster said, make sure your valves are set up within the clearance specs. I assumed you had done that already. That will definitely make it hard starting. My 07 250f was hard starting and after messing with the carb for a few runs I finally checked the valves and reshimmed. It started and ran great afterwards.

Are you completely sure you have fuel getting to the cylinder?

Yeah i sure do. To much I think. Like I told the other guy I finally got it to fire up for 10 seconds. Only after tipping the bike over and letting all fuel spill out of the carborator and motor. It runs for 10 seconds shuts down and won't restart until I tip it over and empty fuel from motor and carb again.

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The zeroed out valve would have created his wet/flooded plug. Shimming the valves would remedy that situation.

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I checked my valves and they weren't perfect at all. Both exhaust side were at .20 and I think my middle intake was at .15. But the other 2 were both like .25mm so those are about .10 over. I don't have any shimms right now so I'll have to wait to fix that. But being high is weird right? I see everyone talking about zeroed and really low but have no idea what it means when those numbers are high

Edited by romansam

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Ok how did you fix the flooding? I think that's my problem. I can get it to start only after tipping my bike over getting all fuel out and trying to start it

Mine was flooding because my fuel screw would not turn all the way in. The last couple threads inside the carb were stripped/cross threaded.

Basically when I thought it was in it was actually 2 1/2 turns out. I ran a tap through and fixed it.

Apparently I'm the only one in the history of carburetor ownership to have had that problem. Your carb troubles, if that's what it is, is yours and yours alone. Lol

As for your valves....yes it does seem odd that they are too loose. They get tighter with wear. I'd guess someone haphazardly shimmed them at some point.

It was my center intake valve that had zeroed (.000) out. As in, I could not fit any feeler gauge in there. The center intake valve is the first to tighten up.

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It's possible, with your 2 intakes bing so far out, that it's making it hard to start and run. I'm not sure that would cause a flooding issue though.when you had the carb apart, did you put the o-ring and washer back on the pilot air/fuel mixture screw? That can create a host of fuel problems... don't ask me how I know!

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I'll take the carb back apart and check it out. I've never done carbs befor this so I just followed a video and had no idea how to set anything. So I did screw the fuel screw 2 and half turns out like someone recommended. Now wait is that 2 and a half full 360 turns? As far as valves go maybe I'm just doing it wrong

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