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Jtsstn13

99 yz400f carb help, stripped needle/main jet

5 posts in this topic

Hi, first time poster here. I recently bought a 1999 yz400f and have been going through the carb as a maintenance thing. I had been distracted from the project, and finally got time to pick it back up today. I was checking the torque of the main jet and ended up shearing the threads off. The threads of the main jet are now stuck in the needle jet. My question is how do i approach fixing it. The jetting is completely stock, as is the engine other than an add-on stator that acts like a flywheel weight.

1) Do I replace with all stock parts, or do I take the opportunity to rejet? The few miles I was able to ride it before tearing it down didn't show any problem with the stock jetting. Is there a recommended change to go to from the stock jetting (I believe 180 for the main)? I am running the stock exhaust and plan on getting an exhaust with a spark arrestor or running a PMB end cap.

2) It appears that the needle jet is not one that is replaced when rejetting. It also appears to be extremely expensive. If I can extract the broken threads of the main jet out of the needle jet, do I only need to replace the main as part of the rejetting? Or does the needle jet get replaced while tuning?

Thanks!

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get a new main and needle jet. thats what i would do. and to get the shards of metal out try compressed air or wire.

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I should also add the stock main jet is marked as a 180. At the time of tear down, I thought i remember reading that this is the stock size on a 99. The jetting posts for the 98-99 bike says the stock jet is a 175. Does anyone have an input on what main jet to replace it with? Should I stick with 180 or run something richer?

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get a new main and needle jet. thats what i would do. and to get the shards of metal out try compressed air or wire.

DO NOT UNDER ANY CIRCUMSTANCES RUN A WIRE THROUGH ANY ORIFICE UN A CARB.! It will put you in a far worse predicament than you are now. Carb. cleaner and compressed air are the only things that should be used to clean a carb.

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DO NOT UNDER ANY CIRCUMSTANCES RUN A WIRE THROUGH ANY ORIFICE UN A CARB.! It will put you in a far worse predicament than you are now. Carb. cleaner and compressed air are the only things that should be used to clean a carb.
It MAY cause a problem, but if reasonable caution is used, it's safe enough. In some cases, it's the only way to remove a varnish deposit.

The risk is that altering the shape of the entry, exit, or bore of any fuel metering orifice can potentially change the way it works. This is especially true with the smaller jetting circuits, like the pilot.

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