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cereal killer

Difficult and inconsisent starting. 2008 yz450f

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My 2008 yz450f will start with 3-6 kicks when cold. When I stall it when it's hot though, it can take 7-9. It's not a big issue when I'm trail riding, but when I'm 2hrs into an enduro... It can be a chore. When hot, I pull the hot start and slowly push the kick lever until it gets firm. Then bring the lever back to the top and give it a full kick. Is there another trick to it I'm missing?

My old 426f started 1st or 2nd kick no matter what. With this bike, I'm consistently one of the last riders to leave the line since I have to kick it several times to get going!

I checked the valve clearances. They're all nearer the tight side, but still within spec. I also took apart the carb and cleaned it the other day. I repacked the silencer. The jetting is stock. I live at ~3500 feet, and many of my riding areas are above 5000. Could the jetting be the source of my problems?

I don't have any engine mods or an aftermarket exhaust. Everything engine-wise is stock. I checked the jetting database, but there's nothing close to my elevation with a stock setup to compare to.

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At your riding area, try to see if your pilot circuit will adjust out according to these guidelines:

http://www.thumpertalk.com/forum/showthread.php?t=327405

You can make the bike easier to cold start by giving it more of a prime (twist the throttle a couple of times). If it doesn't start on the first one or two, prime it again. The most common reason for it not to want to start hot is that it's too rich on the idle jet.

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Take the time to do what gray says, your right leg will thank you. It's so cool when your bike starts first kick. Turn your gas off if parking your bike for a while.

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I haven't been out riding yet, but I checked in my backyard today (my neighbors love me). I think I was hitting peak idle somewhere between 1&1/8th - 1&1/4 - turns. My house is at 3550 ft. Should I expect it to change much when I get riding in the 5000+ areas?

I think this is definitely the right track though. I had it set at 2&1/4 before, so this is a pretty big change. According to the instructions in the link you sent me gray, it should be in between 1-3 turns. Since I'm nearer the lean side, would it be worthwhile to try a leaner jet? If so, how much leaner should I try?

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The pilot is a 45. Everything is stock so 160 main, starter 72, leak 55.

In case it's relevant, I have both "twin air" and "no toil" air filters. Haven't noticed any difference between the two.

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I'd run it as is and do a final trim adjustment at your riding spot, then see how it does. The 45 ought to be about right.

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Went out to a riding area at about 5000 feet yesterday. After playing with my fuel screw, it looks like I settled at a setting between 3/4 and 1 turn out. However, I didn't notice any improvement in starting. I remember stalling it on an uphill, and kicking it solidly 9 times before it fired up. When hot, it always seems to take at least 5 kicks and sometimes twice that.

When making the adjustment, I was able to turn the fuel screw all the way in before the idle missed. Is that normal?

I'm also noticing a stalling issue when I go from gas on, off, then give it a little throttle again. I'm not talking about dumping the throttle, just a quarter turn or so. I admit I might not be rolling it on smoothly, but I'm not opening it up that far when it happens.

EDIT: I should add, temps were in the mid 20's (Celsius, or ~77 fahrenheit) and it was pretty muggy out.

Edited by cereal killer

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Went out to a riding area at about 5000 feet yesterday. After playing with my fuel screw, it looks like I settled at a setting between 3/4 and 1 turn out. However, I didn't notice any improvement in starting. I remember stalling it on an uphill, and kicking it solidly 9 times before it fired up. When hot, it always seems to take at least 5 kicks and sometimes twice that.

When making the adjustment, I was able to turn the fuel screw all the way in before the idle missed. Is that normal?

With that screw adjustment, the indication is that the pilot is too rich, and you should try a 42. The reason you can close the screw all the way off and not kill it is that there are two separate discharge passages running from the pilot circuit into the air stream. The screw meters one and the jet the other. The jet baselines the circuit and the screw is used to fine tune it. So especially in the case that the jet is larger than it should be, the screw can be fully seated and the bike will still idle.

Restarting a stalled hot engine is usually a problem of the engine having been partially flooded, so the hot start comes into play. This is normally noticeably more difficult when the bike is pointing significantly up or downhill.

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I've had a chance to try out the new jetting at a few of my riding spots now. Massive improvement. When hot, it seems to take a max of 5 kicks now, with 1-3 being pretty standard. Cold is a bit inconsistent still, but I think that's mostly me figuring out how much to prime it. It seems to want no more than one twist of the throttle. I'm not as worried about cold starting anyway since when I'm do that, I'm not tired yet.

It was hot yesterday (around 32C or 90F) and I noticed that I had the fuel screw between 1 turn out and 7/8ths depending on whether I was at the top or bottom of the mountain). Should I go with a smaller jet still? This is way hotter than usual around here, so I'm inclined to leave it as is. Especially since my hot start problem seems to be resolved now. But I guess this is still on the bottom side of where it should be.

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It was hot yesterday (around 32C or 90F) and I noticed that I had the fuel screw between 1 turn out and 7/8ths depending on whether I was at the top or bottom of the mountain). Should I go with a smaller jet still? This is way hotter than usual around here, so I'm inclined to leave it as is. Especially since my hot start problem seems to be resolved now. But I guess this is still on the bottom side of where it should be.

That does still point to a too large pilot jet, but it sounds like you're getting pretty close. If you're happy with the way it runs, you might leave it that way, as it would give you the flexibility to ride at lower altitudes and in cooler weather without having to make any other changes.

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Thanks Gray. Yeah, I think I'll leave it for now. At least until I can see how it does in cooler weather. It's been much warmer than usual lately, so I'd hate to get it perfect for the heat and then just have to undo it when it cools down.

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