New to YFZ

[moore020]

I am new to the YFZ. Yesterday I bought a 2004 YFZ 450. I dont believe that it has any engine work done to it. It does have the FMF Powerbomb Full Exhaust.

It is backfiring on deceleration, I am thinking that it is running lean. Any guesses to what it needs to be jetted to? It still has a stock air filter on it, but I plan to change it to a No-Toil.

What are some of the first things you would do to a YFZ if you just bought it used?

BTW, does anyone have an electronic manual they could send me?

[JoePA]

Welcome!! to the YFZ world! You are going tolove the YFZ!

If it were me this is what I would do. Get yourself some good oil, oil filter, air filter, new plug, GYTR jet kit, 35 or 40 leak jet and a Hot cams shim kit.

First thing is lets check those valves and see how they are doing. Get the front plastics off and remove the gas tank, Pull the valve cover off and Set the timing so it's at Top Dead Center (TDC) Once it's up on TDC you can also check to see if the Cam mod was done. If not I recommend that you do that. Check your valves to see if they are in spec. You may need to replace some shims in the intake valves to get them into spec. If you need to reshim and do the cam mod..re shim the valves then do the cam mod last.

Once you are done there. Pull that carb off and go through it. Pull the bowl and see what jets are in there. The stock jeting is very lean from the factory, probably why she is popping on decel. Replace the pilot jet with a 45, main jet to a 165, leak jet to a 40 (located in the bowl) Pull the top of the carb off and replace the needle witht he one supplied in the GYTR kit. Place the clip in the center position. Reinstall teh needle. On the sideof the carb where the throttle cable goes in remove that cover. If the throttle cable is still hooked up, hold the throttle wide open and adjust the screw with the spring on it so it is just touching the cam then release the throttle. Adjust your idle air screw located on the bottom of the carb, front side of the bowl and adjust it so it's 2.5 turns out. Your carb is now set up to a pretty good starting point. Reinstall the carb.

Remove the airbox lid and keep it off (put iin on the shelf somewhere). Put in a good foam filter..the No toil is a good choice. You are now set up to run pretty darn good. If it still pops on decel you can adjust the idle air screw out to say 3 turns If it's still popping on decel you can up the pilot to a 48 and go back to 2.5 turns out on the idle air screw. Also look into purchsing the Idle air screw that is longer so you can adjust it without removing the carb. The one made by R&D ( R&D flex Jet) is really nice and thats what we use. R&D flex jet (http://www.magicracing.com/RD-Keihin-FCR-Flex-Jet-Air-Mixture-Screw_p_5182.html)

last but not least change your oil!! Keep fresh oil in her and she'll runa long time for you!

I believe I have a service manual on file somewhere I'll check to see if I can find it. If not do a search the service manuals are out there. Good luck with your new ride and enjoy!!

[moore020]

Thanks for all of the advice. It currently has a jet in it that is shorter than a normal jet but it has an adapter on it with a flat head slot that looks like it reduces the fuel flow, any ideas?

What does the jet kit you are talking about do?

[JoePA]

The jet that is in your carb now sound slike a JD jet kit. I may be wrong. I believe it uses Mikuni jets instead of keihin Jets. I'm not a fan of the JD kit or whatever kit that is due to the fact if you want ot change your jets by just removing the cover from the bottomof the bowl its kind of a pain.


The GYTR jet kit is a few main jets, two pilot jets and the NCVQ needle. The kit is basicly a range of jets to make your quad run best. kind of taking the guesswork out of jetting....or aleast getting you close.

By installing the jet kit, Try what I recommended in my earlier post as far as jets, doing the cam mod, removing the air filter lid and installing a slip -on you will get the most bang for your buck.

Do a searh to see wih is running in or near your area and has similar mods to you to get an idea as to where you need to be with your jetting. If you ahve any questions I'll IM you my cell and feel free to give me a call or text and I'll walk you throught he process.