Bike won't run properly after oil change.

Try to keep your head up, this seems like an odd problem and uncommon to the yz450f (and 4 strokes in general).

Try taking the top engine mounts off, they mount to the inside of the frame and to the head. That'll give you a little more room to work with. I usually end up seperating the gasket from the head cover, like you I find it next to impossible to get the cover off with the gasket attached.

I'd think the screen on the petcock would be fine, but it's something that's relatively easy to eliminate as being an issue.

If I were you, the first thing I'd do is I'd play with the idle adjustment screw. I'll take a look in my manual (2009) to see what it says as far as where it should be set - if it says anything at all. I'd try turning it in 3 or 4 rotations, something that will be noticeable and then with the bike running I'd turn it down to a normal setting.

The next thing I'd do is I'd check the timing & clearances.

Don't you just love the process of elimination ?

The cam cover comes out with the gasket on the cover, but barely. As pointed out, the upper mounts have to be removed first. Then raise the cover, peel the half moons loose from the cover so they cab turn out horizontally, and remove it by rocking and sliding it to the right side of the bike. The gasket is pretty tough, and not very likely to tear.

I had the engine mounts removed when I was trying to pull the head off, as well as had the half moons pulled out of the cover...it just seemed like I was really having to force it, and was afraid of scratching it on the cam chain and sprocket assembly.

So, got the cam cover off...timing is perfect. Tried to measure valve clearance but the feelers I got are too wide side to side to fit in the space...will have to get some other ones. Any really good ones I should get (Motionpro etc). I'm not sure what else it could be now other then valves are out, or carb still has something up with it?!?

Edited by Fabulous

I cut some of my feelers with a pair of scissors, because as you've said they were too wide. I don't know if that creates an edge and makes them thicker or not, but I did it anyway.

I cut some of my feelers with a pair of scissors, because as you've said they were too wide. I don't know if that creates an edge and makes them thicker or not, but I did it anyway.
It does alter the edge, and often significantly, but if you use it right, the edge should never be between the cam lobe and lifter when you measure anyway, even with an un-modified feeler.

I just use standard 4" gauges, and have never had to trim them for a 450. I don't know where all the fat ones come from :smirk:

Would the jet at the back of the carb (the one where it meets the boot) make the bike not want idle? I can't seem to find a set of feelers anywhere that will work for what I need, so I may have to order some but until then I want to cover ALL the bases.

Would the jet at the back of the carb (the one where it meets the boot) make the bike not want idle?

If it's plugged, yes.

If it got water in it would it not get flushed by the alcohol I added, or is it a good bet to just pull it and clean it? Other then my valves I can't think of anything alse it could be...

Just had a similiar problem with my 2005 WR450. I installed a new slip on and bascically put the bike away for a few months. Went to ride it last week and it took forever to start would not idle and only ran with the choke on. Being a two stroke guy myself I was thinking o crap. The thing that threw me off was it ran like a champ before. What I ended up doing was adjusting the fuel screw out about 3/4 of a turn. Right at 2 3/4 turns. Bike runs like a champ. Try adjusting the fuel screw a little and see if that helps.

Good luck.

I've done that...no change. Bike always runs best at 1.5-2 turns out on my Merge fuel screw.

At this point I would just step back and retrace all my steps. Check everything you touched during the oil change. Pinch a wire with a bolt? Smashed a wire with a tool? Knocked a connector loose with your other hand? Pinched a wire with the straps coimng back from the track? I would just retrace as much as you can and see if there is something stupid that isn't related to the carb. Check the air fliter? I'm just throwing out the stuff I look for when I have a problem that doesn't seem logical.

If it got water in it would it not get flushed by the alcohol I added, or is it a good bet to just pull it and clean it?
If the pilot air jet has water lodged in it, the alky won't ever touch it.

Just a shot in the dark, maybe the TPS got water in it?

Mines a 2008 so it would have the 4 bolt stator plate...

I know of at least one '08 that had a stator fail. Test it.

How about water down in the spark plug hole? If you did a really good washing, it's possible that water made its way down in there. Bike won't run worth a flip if water is down in there. Some of the other suggestions are a bit of overkill if the bike ran fine earlier.

ALSO, I remember a similar issue on my 04 YZ250F. Used to run perfectly. Then it just would not idle right. It would pip and pop and shoot flames out the exhaust. AND it would get hot quickly. Titanium pipe would glow red. !!! I was stumped for about 2 weeks. Valves, Cam Timing, blah blah blah. None were the problem.

Turns out the Pilot Jet inside the carb was actually clogged (thanks to Ethanol Fuel evaporating and leaving the dreaded residue inside.) It was clogged so bad I couldn't even poke through it with my carb jet wire set.

Soooo, I replaced the Pilot Jet with an "unclogged" one. Problem solved.

This was after removing/cleaning the carb like 5 times and I don't know what'all...

This problem almost made me tear my hair out. One small issue that made it run like crap was all it was. After that fix, bike runs perfectly again.

Check all jets for any clogging - especially Pilot Jet. Make sure you can actually see through the jet hole. Don't just assume it is clear because you blew air through it. (I did the same thing and assumed such.)

P.S. DO NOT LEAVE PUMP GAS that has ethanol in it sitting in your carb. When the fuel evaporates it leaves a powdery residue that is notorious for clogging jets and other tiny carb passages. I personally mix 110 race gas with pump gas and problem solved. Or you can use StaBil in your fuel. Those of us who don't get to ride all that often have this problem.

Check all jets for any clogging - especially Pilot Jet. Make sure you can actually see through the jet hole. Don't just assume it is clear because you blew air through it.

The difference between a #45 pilot and a #35 pilot is 0.10 mm (.0039"). You might see that if you held them both side by side, but the fact that you can see through the hole does not always mean there isn't a significant layer of varnish in the jet, either.

If you don't have, or don't trust yourself with a set of small number drills, try soaking the jets overnight in straight fuel injector cleaner, then blowing them out with high pressure air.

I know this post is old, but if you ONLY did an oil change and wash job there should be no water in your carb. thats alot of water to fill the exhaust all the way back to the carb,(and past five valves!) You got some water....might be very little... on the spark plug boot(down at the plug), it only takes a little moisture to get a misfire. remember the spark will always go to the place with least resistance.

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