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Another Rejet and Needle Question

497 Views 3 Replies 1 Participant Last post by  GASoline71
I have a 2008 YFZ450 that I bought a couple months back and am finally digging in to it to see what I have. Guy I bought it from was clueless to any modifications as he bought it the way it sits now. This thing rips pretty good but I think it has more in it. It also has a wicked stumble sometimes at part throttle when you pin it, it will damn near throw you over the bars as you are anticipating it to go, and it stalls out and sometimes dies.

It has a full Yoshimura RS-2 exhaust and also has an Athena 480 BB kit on it. I pulled the carb out today to see what was in it and what I was dealing with. Someone rejetted it already, and there is a 175 main and a 45 pilot. The needle has 7 positions on it and the clip is the 7th slot. I don't know if it is a stock needle or an NCVQ. Is it easy to tell what needle is which (stock vs. ncvq)? I did a search and couldn't find an answer.

I'm at sea level and I'm thinking of moving to a 178 or 180 main and a 48 pilot and moving the clip up a couple of slots to the 5th slot. Smart move or nah? Any advice would be awesome.

Thanks for helping out a new guy.

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I forgot to mention that the rig has been getting a little warm during rides and the "overheat" light came on last ride. The radiator is full of a clean blue coolant and the reservoir out back has a bit in it too. The reservoir is pretty scummed up inside, so I need to pull it and clean it out. I have not ensured that the fan is working yet, but wanted to check to see if it was jetted way too lean. Someone has rejetted, but I'm not sure if it's enough. Going to check the fan today, and see if the radiator fins are clear of crud.


I rejetted to a 180 main and a 48 pilot. Installed an NCVQ needle on the 5th clip. The leak jet has been blocked off by whoever had been in this carb before. Looks like they were on the right track. I also did the zip tie mod to the accelerator pump. Then noticed that the accelerator pump has been upgraded to a Boyesen QS3.

I'll report back...

Been awhile... LOL... since I'm the only one in this thread, I can keep it for me to look up later. ;)

I ended up having to replace the water pump seals and a new water pump impeller shaft. Also had to get a new head pipe from Yoshimura as one of the prior owners tried to get a little creative attempting to weld a new flange on the titanium head pipe. Had to wait almost 6 weeks for a new head pipe from Yoshimura. They no longer make the titanium exhaust for older YFZ's so I had to get a new stainless steel head pipe. However, it fits like a glove into the old titanium mid-pipe.

Anyhoo... after all of that, I got it running today and holy crap does it rip! What a difference a new (non-leaking) head pipe and a rejet of the carb made! I was really thinking I had a dud on my hands until this afternoon before work, when i got it started up and took a test ride. Super happy with it!

I guess I need to take a pic or 2 of this thing and post it up here.


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