Wont run without the choke. yz450f "03" - Yamaha Forum : Your Yamaha Motor Products Community & Resource
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post #1 of 5 (permalink) Old 06-24-2011, 12:27 AM Thread Starter
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Wont run without the choke. yz450f "03"

I just got my 03 yz450f and the guy told me that one of the jets might be clogged because it would only run with the choke out. I took apart the carb and cleaned the jets, the pilot jet was clogged. After I soaked it in solvent I was able to see through it. So I put it back together and it's still the same, maybe it got clogged again. So, I was wondering if anyone has some input? Oh, and is it bad for the bike if I run it with the choke out?Dang!
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post #2 of 5 (permalink) Old 06-24-2011, 06:18 PM
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If PO tried to tune it with plugged pilot circuit, that thing may be all out of whack.

Lots of critical circuits on that carb. You may have cleaned the jet, but did you clean the passages in the carb body? Dis-assembling and soaking the entire body would be the ideal way to prevent continued fighting with it. Time for a kit, and a good soak. Be sure to blow out all the ports/passages. If the thing is really caked up and passages are plugged, you can use a welders tip cleaner or welders tip drill set (example http://www.acehardware.com/product/i...ductId=1292551) to remove most of the muck. Just don't force the cleaners or drill bits in, and don't remove any aluminum. The passages are a certain size for a reason. DO NOT use this procedure to clean the actual jets, just the bored/machined orifices/passages in the carb body.

Last edited by rooster; 06-24-2011 at 06:30 PM.
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post #3 of 5 (permalink) Old 06-26-2011, 01:58 PM Thread Starter
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Okay, so I cleaned it out like you said. I took out all the jets and opened up the carb and blew compressed air through the holes the jets were in. I also found that the pilot air jet screw that lets air in was screwed in " all the way"! I un-screwed it about 2 turns out like the mechanic at yamaha said. After all of this the bike now runs " without" the choke. Yay!
But, I have another problem now. The bike will idle when first started but after I take it for a spin and as I come to a stop it dies. As I ride, I have to give it gas when I hold the clutch in. I have now changed the spark plug and it was dark gray. It starts up easier than before but haven't taken it out yet. I will know by tomorrow or the day after.

Last edited by Tgigser; 06-28-2011 at 12:13 AM.
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post #4 of 5 (permalink) Old 06-28-2011, 08:29 PM
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That's good news. The plug might have been coated from running so rich. Correct jetting should give you a tan to light chocolate color. The ideal way to read a spark plug is with several "chops" at different throttle settings, under load. The plug shouldn't be "read" at the tip (ground strap), but rather down at the base of the ceramic insulator. That's a whole different story. Do a search.... I'm sure it's been explained many times on this forum.

IMO, it still sounds like it's running rich. I'm not a guru on the 450F, but most carbs are set for ideal adjustment at 1-1/4 to 1-1/2 turns on the air screw. Anything either way from that means you need to contemplate a different pilot jet. And, the pilot jet will have a lot to do with how your motor idles.

Good luck.
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post #5 of 5 (permalink) Old 01-29-2015, 03:48 PM
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Great information. Thanks for the posts.
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