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fowler175

crazy jetting?

5 posts in this topic

OK, so I just changed the head gasket in my 04 yzf450, got it all back together, and now it won't run. However, while I had it apart, I changed the pilot from a 45 to a 48 because of a bad low speed popping when I let off. I had assumed that this was due to a lean condition in the slow curcuit, but maybe it wasn't? Could I be way to rich now and that's why it won't fire. I just bought it and still don't have a manual, so I don't know what the stock jetting is. What I DO know is that I have a very healthy spark, the timing is correct yet when I pull the plug, it is soaked. Even after draining the carb and kicking repeatedly with WOT, the best I could get was a half-assed backfire out the exhaust :applause: . I will be changing the pilot back today to try it again. Sound like I'm on the right track? or is there something else I should be looking at. BTW, the bike is currently running a 172 main, 45 pilot, 72 whatever it is, fuel screw @ 1 3/4 and I have yet to check the needle (will do that later today). Is this way outta wack or pretty close to average. Oh, the bike is bone stock otherwise. Thanks for any info

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I have no experience with the 450s but from what I see there, you are definately not on the lean side...

Have a look at the yamaha -motor website and find the parts catalog. By clicking on the carb, you'll be able to see the stock jets (they are labelled "STD" in the table just beside the part number).

The 72 is your starter jet... I think 72 is stock. I would guess your 45 pj is stock as well. I don't think the 172 main is stock though but I could be wrong. The 426 were running 162 mains at sea level.

Also consider that you are in BC... which means high humidity I guess. This tends to "artificially" richen the mix as oxygen is partly conjugated with water making it less available for combustion.

Are you at see level or do you ride the Rockies?

Go back to your 45 and try to adjust with the fuel screw before going to the 48 pj.

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id say your prolly rich on the main,your pilot might be just fine though.I swapped out the stock pilot to something richer in my 450 because it was too lean.I think i went to either a 48 or a 50 but im not sure off the top of my head.

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Obviously, you have some type of rich condition, remove your choke, clean and lightly lube the plunger and reinstall. I would also check you float bowl height, sounds like it might be to high. Lastly, make sure you have enough play in your throttle cable to prevent the carb. slide from lifting prematurely due to lack of throttle cable play.

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lemme ask this,before you changed the pilot out,how did the bike start when cold?

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