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mxmaddman

yz450 issues

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2009 450.. It wont run right. I have cleaned the carb, timing is spot on and checked the valves. the tightest valve is the middle intake at.011. the thing constantly runs lean. I replaced the entire hot start cable and plunger. I have dissected the carb like 4 times and blown air and shined a light through every hole in it. the pilot was increased to a 48. The o ring on the fuel screw looks ok and the slide plate is on with the hole on the bottom. I cant figure out why its running so lean. It will die and wont idle and is a pita to start. header gets beat red in 10 seconds when the choke is off. It acts like a carb issue, but I cant think of anything else to check.

Any ideas at all will help, seriously even long shot ideas are welcome at this point.

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Just for grins, let's check the vacuum plate on the engine side of the slide and be sure that the "square" side with the hole next to the edge is down.

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Just for grins, let's check the vacuum plate on the engine side of the slide and be sure that the "square" side with the hole next to the edge is down.

yup, the hole is down on that. could it go bad?

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If the seal were missing or the plate had a corner broken off, yes, but it's hard to imagine the plate being damaged so soon.

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Your ".011" middle intake valve, is that in thousandths of an inch, or mm?

I meant its .11mm. The spec i think is 10-15.

The shims are factory still.

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Any other ideas? I still cant seem to get it correct. If the pilot is clean and the passage to the paj are clean and the fuel screw is all clean.. what could it be? I mean that's pretty much the whole pilot circuit right?

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2009 450.. It wont run right. I have cleaned the carb, timing is spot on and checked the valves. the tightest valve is the middle intake at.011. the thing constantly runs lean.

I replaced the entire hot start cable and plunger. I have dissected the carb like 4 times and blown air and shined a light through every hole in it. the pilot was increased to a 48. The o ring on the fuel screw looks ok and the slide plate is on with the hole on the bottom. I cant figure out why its running so lean. It will die and wont idle and is a pita to start. header gets beat red in 10 seconds when the choke is off. It acts like a carb issue, but I cant think of anything else to check.

Any ideas at all will help, seriously even long shot ideas are welcome at this point.

Couple of things. I noticed your in Penn. I'm guessing you haven't been riding very much, as the east coast got hammered with storms recently. Was this bike put away for a while, and you attempted to restart? If so, I'm guessing it ran fine before? Kinda seems like you threw some parts hoping for a fix, but you had some good info. that stood out.

I went through an issue on my daughters xr70, where it was running great on start up, but then when it got warm, it was too rich. I had just picked it up, and the bike had sat. I also cleaned out the carb (carb clean and compressed air), and replaced the pilot as it was blocked. It would still run rich once it was warm. It was suggested early on to do a carb dip/bath. I thought that was a silly idea as I had cleaned out the carb. We'll, long story short, that was the issue. Today's gas doesn't hold up well. Carn dip is cheap, and will only cost you approx. 24 hours. It can't hurt!

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yea, I was thinking about soaking it. The only thing with that would be the rubber seal in the carb body thats not serviceable. I worry it will swell up as rubber tends to do in the carb dip.

Im thinking of completly blocking the choke port off and hot start off and starting it to see if I can exclude them as a culprit. Then the only thing left it could be is the slide plate o ring. :smirk:

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What type of gas do you run? This isn't really a fix but I had a friend that had a similar problem that we couldn't find and he was running 93 octane so he switched to 87 octane gas and that helped somewhat. Gray correct me if I'm wrong but higher octane gases run leaner.

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What type of gas do you run? This isn't really a fix but I had a friend that had a similar problem that we couldn't find and he was running 93 octane so he switched to 87 octane gas and that helped somewhat. Gray correct me if I'm wrong but higher octane gases run leaner.

I run 93.. but i did actually try 87 and it seems to run better. I am going to try to take a video ... but its cold as heck out so it seems to be running better in the cold, but its still hanging a little.

the biggest pain is when its been ridden for a while. generaly it starts up and will run and rev for lke 40 seconds then will die. If it starts back up then im good. but if it doesnt i have to kick it WOT untill it revs and dies then pull the hot start close the throttle and kick untill it starts and hope i can rev it and keep it running.

When its hot it acts too rich, when its cold it acts lean.

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Gray correct me if I'm wrong but higher octane gases run leaner.
No problem: you're wrong.

Very highly oxygenated fuels, some of which are high octane race fuels, run leaner, but not that much.

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ok i might be onto something now... the slide seal appears to be a little loose. If i shake the slide plate around the seal goes up and down a little in the groove. is it normal for it to be a little loose when attached to the plate? I dont think it is. Does anyone know where i can find pics of one to make sure it on right?

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ok i might be onto something now... the slide seal appears to be a little loose. If i shake the slide plate around the seal goes up and down a little in the groove. is it normal for it to be a little loose when attached to the plate? I dont think it is. Does anyone know where i can find pics of one to make sure it on right?

I hope I'm understanding ya here....... Are you thinking maybe that seal (#11 in the "exploded view" that Grayracer513 gave..... How come all those parts keep "exploding" in our manuals? Never have figured that out.... :smirk::lol: ) needs replacing that stays on the wear plate? I've read a magazine article stating you need to replace that seal everytime you have the carb apart, but I've gotten away without replacing it that often..... If you do replace it (they're not that expensive....), pay close attention to how it comes off, & put the new one on the same way it came off. It's hard for me to verbalize, but the "bigger" outside diameter of that miniscule seal fits up into the actual slide, if that helps any...... The one I recently put on does fit marginally tighter than the one it replaced. Maybe my old one wasn't all that bad. :rant: It still seems like the wear plate fits a little on the "loosey goosey" side to me, but the bike seems to run fine.... :p

Jimmie

Edited by Diesel Goober
Forgot to add something....

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The picture in the manual doesnt show how the seal goes on. I think Its the seal for sure. I greased the seal a little to test and put it back together. When I fired it up it ran good with very little idle hang. ordering a new one tommorow.

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