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Thunder Alley Jetting


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After installing to pipe, ride it. When you get on it hard, if the power flatens out on the top end, bump the jet up one size. Most people just bump it up one size anyway. Once you bump it up, you should feel a big change. Hold on and be ready for it.

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TMoo is right bump the main up then take her for a ride. After that change one thing at a time. It took a little while to get the jetting worked out. I still think the 48 pilot is to rich but the next size down is a 45 and that is too lean.

I run my T/A with the following adjusted for weather and altitude.

EMN #4, 160-162 MJ, 48 pilot, 1 turn out air screw

FYI If you run the spark arrestor you'll have to go down 2-3 mj steps. Did you buy the complete system or just the muffler?

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I'm running from 500-4000' in So. Cal. any thing over 2000' and I put the 160 in.

I would leave your jetting alone and take her for a ride before changing anything. That's a good place to start. You didn't spec a pilot I found the 48 too rich and the 45 seems too lean so I went with the 48 just to be safe.

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48 is a good place to start. Sounds like your jetting should be close. It took a little testing to get mine to where I feel it's spot on though.

Better bottom end than stock and a harder pull through out the powerband the motor "barks" now- Rev's out much faster. Felt like a 4-5 hp gain. Mid to top end is where you'll notice the additional power most. I rode mine back to back with a new 525sx and my motor with the pipe reved out faster and pulled harder.

Let us know what you think after you ride with the new pipe. 🙂

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  • 3 weeks later...

Hey Travis thanks alot for the specs.I just talked to Bob yesterday and the pipe is not back from getting coated yet,I told him not to worry there is no rush, It doesn,t show on my signature but I,am from the northland (Canada)so it will be a couple of months before I need it!

I disassembled my carb cleaned it the diaphram for the pump was full of crud and jetted one size richer. I was really worked up to install the new fuel screw I got from zyptye racing with the nice knurled Knob that hangs below for adjustment,I bought six of them gave them to my buddies for christmas they slipped into their new yz450,s ktm450,s and crf,s no problem I went to put mine in the 520 and the hole in the bowl is oblong and it would not go up ,okay filed it round no problem,it will not bottom out because the knob hit,s the bowl plug,give that a little turn to get the flat side to the knob and a slight file on the flat side and down it goes., turn it back 1 1/4 turns and there is no tension it, it would vibrate out,oh well back to the stock brass one I,ll just have to get a new 450 to go with the fuel screw.

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Hey All,

I put a TA on "Motoman393" 2003 YZ450 and moved up to a 170 main jet. This was up two sizes from stock. Makes a HUGE difference in the bike all across the power range. Darn glad I purchased a TA. Pics can be seen in the YZ450 forum.

🙂

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