Does this sound like a jetting issue?

15 replies to this topic
  • tank3d

Posted August 31, 2012 - 04:03 PM


2003 WR450F - Uni filter, FMF powercore.

This bike is new to me and is from Arizona, I am in Oregon. The previous owner said he had the carb rebuilt in Oregon, but didn't ride the bike. I have no idea how the bike is jetted.

When I ride the bike, I can feel the bike surging and the exhaust will pop sometimes. This happens primarily when cruising...keeping the throttle in the same position, trying to maintain the same speed. It seems to go away when under a load (uphill), or when accelerating. The exhaust will pop while decelerating, or after letting off the throttle after winding up the rpm's.

What do you think?

Edited by tank3d, August 31, 2012 - 04:04 PM.

  • tank3d

Posted August 31, 2012 - 04:28 PM


Also, the exhaust (head pipe) is super hot. Riding in shorts, it burns my leg even from a distance.

  • mtahoe

Posted August 31, 2012 - 07:41 PM


Sounds kinda normal, try adjusting the air mixture screw..

  • MANIAC998

Posted September 01, 2012 - 02:41 AM


It's normal. But wearing shorts while riding isn't!!! There's no way I would ride while wearing shorts, but that's just me. Seriously though, at some point, your going to have to know what jets you have in that carb. We're going to have a hard time helping you, if even you don't know what jets are in there.

  • GlennR

Posted September 01, 2012 - 08:33 AM


I don't know anything about carbs, but I can tell you that the TPS on the carb creates problems with the stock ignition on most WR450's that are ridden on the street. There is an aftermarket CDI by "DynaTek" that cures the problem, but it's $290 on ebay. An inmate had one for sale that he was generous enough to allown me to "try before buying" because I didn't want to be "stuck with a $300 paperweight" if it didn't work. The DynaTek does work, my bike runs like a different bike now. It's an incredible difference. Runs smooth as a street bike on the street now, and starts almost before I press the starter button. DynaTek should offer a "try before you buy" on these things because it is hard to believe that it will work so well.

  • Leardriver

Posted September 01, 2012 - 08:51 AM


Like Maniac sez, you have to look and see what is in the carb now. All other suggestions are just speculation until we know what your baseline is.
I can change the main jet in under three minutes, just as a show of how complex it isn't.

  • Leardriver

Posted September 01, 2012 - 09:59 AM


Don't remove it.

Loosen the carb band clamps, and rotate the bottom of the carb to the left side enough to remove the 17 mm drain bolt, and the the main jet takes a 6 mm little socket. The main jet is brass, and only needs to be snugged up, not put back on with gorilla power.

  • tank3d

Posted September 01, 2012 - 10:50 AM



can you reach other jets, besides the main jet with the method?

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  • Leardriver

Posted September 01, 2012 - 02:33 PM


I can't remember, but I vaguely remember no. It is a pretty tight fit. Your pilot is probably fine, and can be made to work by adjusting the fuel screw.

If your main jet is anywhere close, you probably have a close enough pilot in there. 45 or 48 pilot is fine.

  • tank3d

Posted September 01, 2012 - 03:28 PM


I gave up and took it to the yamaha dealer. They will properly jet and tune the bike with a new adjustable fuel screw for 150 + parts.

  • Leardriver

Posted September 02, 2012 - 06:20 AM


The dealer may put the jets in it that the manual calls for, which aren't even close to what the bike runs best at. The manual was written by lawyers who try to keep the EPA happy, not engineers who want the bike to run its best. I hope you get some value for your money.

Find a TT'er who is close and have them teach you about the carb. It is valuable info that you will never regret knowing.

  • tank3d

Posted September 02, 2012 - 07:11 AM



Thanks for all the info. I have used this dealer a lot in the past for my quads. They re-jetted my quads before, specifically for more power and riding at the beach and throughout Oregon. They definitely will not just switch them to stock. They will do a good job. Of course, if they don't, the work is warrantied.

  • GlennR

Posted September 03, 2012 - 03:04 PM


Good luck with it. Hopefully the low throttle stuttering while cruising on the street goes away. If so, let us know what jets they used.

  • MANIAC998

Posted October 02, 2012 - 05:20 PM


There are some members on here that would say that's a possibility. Me, I'm not so sure.

  • GlennR

Posted October 03, 2012 - 03:57 AM


I'm no expert, but the choke knob shouldn't make the bike run hotter. Hotter means "leaner" and the choke (actually fuel enrichment) makes it richer.

Seems like there's only two reasons the airbox could melt; either the exaust has become too hot, or the distance between the exhaust & airbox as gotten closer.

The stuttering in 1st-2nd gears sounds like a jetting issue.

  • superbike28

Posted October 18, 2012 - 12:06 PM


Hello from Greece....I had the same problem with you for three years and i believed that i can't ride my supermoto wrf-450 (2005) with steady throttle....My jetting is main-168 pilot-48 (stock was 165, 45 )and i have the merge spring in my accelerator pump and an air fuel screw..Everything else is stock in my carb.......My bike was far from perfect but i liked it.....until 3 hours ago.I decided to unplug the TPS and to make the ACV mode (Air Cut Valve)
RESULTS :Mo more popping for me.........WOW....I couldn't believe it
My bike deccelarates perfect now and it comes immidiately in idle speed
I haven't seen no power loss.I think it is faster now and it revs perfect

Until now i liked it ......NOW I LOVE IT


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