Jd jetting

8 replies to this topic
  • TheUSMC1775

Posted March 12, 2014 - 05:54 AM


What's going on folks just received a JD jet kit today for my 2009 yz450f I bought the bike with a full akrapovic exhaust and well it pops on decel,I haven't open the carb yet but was hoping if putting the JD jet kit in will solve this issue. Thank you and please share any other ideas.

  • grayracer513

Posted March 12, 2014 - 07:18 AM


Pops on decel?  Good.  It's supposed to.  If it pops "some" "part of the time", it's jetted about right as far as the idle circuit goes.  If it pops a lot, it's too lean, or could very well have an air leak in the exhaust system.  No popping at all means it's too rich, and will be prone to fouling, hard hot starting, and tend to stall on quick throttle releases under a load.


I don't care for jet kits.  They cost way more than the few OEM parts you would need to correct the jetting with in almost all cases, and mostly don't accomplish anything you can't do with original parts.

  • TheUSMC1775

Posted March 12, 2014 - 08:43 AM


Thank you on that note it pops a lot when in gear when winding out say for instance 3rd gear like gun shot popping, and if there is a air leak on a exhaust repairable or am I gunna have to caugh up some money for a new system? and I doo hear when the bikes warmed up a low ticking possible valves? Thank you for the feedback.

  • grayracer513

Posted March 12, 2014 - 08:58 AM


... it pops a lot when in gear when winding out say for instance 3rd gear like gun shot popping, ...



That's not the same thing as decel popping.  If it pops and shoots ducks while accelerating, it's either got a partly obstructed main jet, the needle is WAY too low (only if it's in the top clip groove), the main's too small, or it really could be a bad spark plug or a faulty ignition connection or component, such as a coil.  Even a flaky kill button.

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  • TheUSMC1775

Posted March 12, 2014 - 09:36 AM


Not while I accelerate but when I let off an decel in a gear, I put a new spark plug in a month ago an maybe had bout 20 mins of ride time on it I'll start with the jet kit first after that I'm lost for words.

  • grayracer513

Posted March 12, 2014 - 09:51 AM


Not while I accelerate but when I let off an decel in a gear,



That's back to the lean pilot or the air leak situation.  Both fixable.

  • TheUSMC1775

Posted March 12, 2014 - 10:05 AM


Thank you you pointed out a lot of key things that I will inspect on the yami now say if it is a air leak in the exhaust whats a good way to test for it.

  • Rocky739

Posted March 13, 2014 - 07:51 AM


Air leak: check that washer is in the head to header connection, replace it if it even looks funny, header to mid pipe make sure nothing is deformed/smashed etc... apply a thin film of high temp sealer to junction, slide together, aka follow manufactures directions!


Jetting: Throw JD crap in trash and take it as lesson learned to not follow hype. Buy OEM Keihin jets (not aftermarket) and needle (Yamaha OE is about the cheapest source, if it was good enough for team Yamaha its good enough for me) follow grayracers recommendations, probably about the same as mine. make sure everything is operating room clean and correctly adjusted (owners manual). Use a good quality fuel screw also (I'm digging my new merge racing one) and that the washer, o-ring, spring is installed correctly. Also check the seal (4FN-14997-00-00) that goes in the slide widgit. If it looks funny, replace it.

Cross fingers at a busy gas station and buy premium from one that you think would sell the most, (I go to a Marathon next to all the import car dealers in town). I also pump a gallon into my car before filling my can  so that I clear out whats in the pump, superstition perhaps?


Here's my jetting in my 2008, no excessive decel pop and runs like a trooper.

Pilot: 48, probably a 45 in summer

Main: 165

Needle: NFLR (std) 3rd clip (std)

fuel screw: 1.5 turns

rest of carb stock, except merge racing acc pump spring and fuel screw, backfire screen removed, twin-air filter and oil, FMF slip-on.


If your simply not comfortable working on it I'd be inclined to send it to Toyko mods, they can do all this for a decent cost and then it becomes a bolt on/off fix.

  • cowboyona426

Posted March 13, 2014 - 08:06 AM


Personally I agree with grayracer, I bought the JD jet kit after hearing many people go on and on about how good it is and I'm not overly impressed.  Wouldn't spend the money again.

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