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By Braaap04,
in YZ400F/426F/450F/450FX

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Braaap04

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Sorry I was working and typed that up really quick before boss man seen what I was doing lol. But I shimmed the valves. Not sure how it started to be honest the first time. Only done valves a few times. But It seemed like I was always off a tooth. Brought the bike to a very knowledgeable guy and found the timing mark on the fly wheel isn't accurate at all. Which would explain why I was never dead nuts on. He worked on it and starts 2nd kick every time now. But another question I do have, the bike is EFI but it still has a "chock" if you will call it that? Again new with efi bikes.. But if its pushed all the way in it will die if not on the gas, and when on the gas runs terrible. If chocked at all it will run mint. Any ideas? 

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Grand Master

grayracer513

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Starting with 2010, the timing mark on the flywheel is no longer located at TDC, so you can't verify it by checking TDC.  It needs to be timed to the marks, and if it's always off by a half tooth or something, that can mean that the timing chain is worn. 

 

The "choke" is actually the cold start/idle speed knob.  Idle speed is adjusted by turning it out for faster, in for slower.  All that it does for a cold start is open an air passage so as to increase the idle speed.  Cold enrichment is accomplished automatically by the ECU, based on coolant temperature.

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Bass Mechanic

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the knob you speak of is not a "choke" it is actually an "enrichment" which essentially does the same thing, a choke chokes off the intake tract causing more fuel to enter the engine on cold starts. an enrichment adds more fuel into the intake tract thereby enriching the mixture. it also tends to make the engine run a little faster where as a choke will slow it down because it restricts airflow.

 

but as for the valves, i would suggest you recheck them cold if they are too tight your losing compression because they aren't fully seated when closed.

hard starting engines are usually the first sign of worn valves or valve seats. if you have adjusted them too tight it causes the exact same symptom

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Grand Master

grayracer513

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the knob you speak of is not a "choke" it is actually an "enrichment" which essentially does the same thing,

 

 

 

That's true of the FCR and FCR-MX carbs, but not of the EFI YZ's.  There is no enrichment function in the cold start knob on any of the '10 or later models.  That's all handled by the ECU.

 

You are correct, though, that it isn't a true "choke" and neither is it on the carb'ed models.

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Braaap04

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So more questions. Went for a small ride through the woods. Bike starts awesome now, runs great except for full throttle. Full throttle and it bogs down bad. I noticed it in 4th. ( didn't have much room to give her ) didn't check through the rest of the gears though.. Timing and valves are fine. But when we did the valves we messed with the TPS to try and fix that "choke, not really a choke" issue I stated above. We put it back to where it was before. But my queation though is that electronically set? As in if it off even a hair could that mess with it?

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