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ShiftRacing144

05 WR450F popping?

25 posts in this topic

When i first for the bike it was popping just like a spark plug was going bad. No big deal. I was racing yesterday, and it was popping everytime i slowed down. It is worrying me, but my dad says its ok. I dont believe him. Someone please help!

If it helpsm the popping sounds like its coming from the pipe, were not sure.

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Could be too lean; was the popping after you'd let off the gas?

Yeah it was

do you have the stock pipe on? if so do you still have the baffle in?

No, the Pro Circuit Ti-4 pipe, whats the baffle? And how do i remove it?

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if the baffle is the little insert at the end of the stock pipe but you don't have the stock pipe on so don't worry about it. you probably just need to rejet and rmovethe ais kit if you haven't.

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Popping on decel indicates a lean condition. But - a little popping is ok. A racket of popping is not.

If you tune the pilot circuit rich so the bike doesn't pop, it won't make the best power when you roll off the idle.

If you've adjusted the pilot circuit properly (slightly rich from peak rpm at a high idle) and the bike still pops badly, your ACV might not be working on your WR.

Do you have the ACV working (cap on the left side of the carb, 2 screws hold it on), or modded to have it cut off? If it's supposed to be working, check that the diaphragm and o-rings are intact.

If none of this helps, check for air leaks on the engine side of the carb and boot and AIS connections.

Fwiw, if you haven't done it already, I'd just disconnect the ACV (per the free mods). It makes the pilot circuit much easier to tune. Same with the AIS. They don't provide any change in performance however.

( I have the same pipe. :excuseme: )

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To add to the great input of others, engine tuners do a free rev and shut off the throttle; you would hear one pop if the bike was tuned perfectly.

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Could be sucking cold air in through exhaust header .

Correct!

Two things cause popping on decel.

1 fresh air leaking into the exhaust system check this first. check the the headpipe to head connection and then the header to midpipe. make sure they are sealed.

2 then check the jetting. the fuel screw should be between 1.5 and 2.5 turns out. if it is not in this range you need to change the pilot jet.

Check the exhaust first

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Could be sucking cold air in through exhaust header .
Correct!

Two things cause popping on decel.

1 fresh air leaking into the exhaust system check this first. check the the headpipe to head connection and then the header to midpipe. make sure they are sealed.

2 then check the jetting. the fuel screw should be between 1.5 and 2.5 turns out. if it is not in this range you need to change the pilot jet.

Check the exhaust first

+1 :excuseme:

I missed this on my earlier post. :smirk:

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Related...just got my 07, and stuttering and popping unless I have a very smooth on-throttle. Pops on acceleration as much or more than decel. Fuel screw all the way in and idles fine, which indicates a rich condition, yes? Does the popping make sense, too, on accel?

Free mods done along with leo vince slip-on, jd jet kit.

Thanks,

Jack

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Hi Jack,

Good questions there. I'll try to answer them well.

Fuel screw all the way in = 1 or 2 PJ sizes too big (rich). Put in a smaller PJ and retest.

If it's popping on accel there are some other questions to ask:

1) does it bog off idle? If so either the needle is in the wrong position or the leak jet is too large or the AP squirt timing is too short (or early or late, or hits the slide, or has insufficient pressure)

2) Does it "pop" on accel. and lacks power or "burble" (like it's drowning in fuel). If popping, your MJ may be too small or clogged and/or your needle is too far down (clip is too close to the slotted end). If it "burbles", the MJ is too big and/or the needle is too far up (clip too far towards the pointy end). Air leaks can make the bike pop on accel. too.

Here's how I tune a carb:

1) get the bike to run. I don't really care if it idles well. This may entail checking the float level. You'll pretty much know if it's a float/needle valve problem if you simply can't tune the carb and it's "always rich" or "always lean" or does weird stuff like run out of fuel at WOT with a fat MJ. If the bike is always lean, check for air leaks on the engine side of the carb (boot), where the hot start cables screws in the top, and the slide cover gasket on top.

2) Run at WOT and find the MJ size that gives the best WOT power. The next size bigger should cause a decrease in WOT power. Use the last size that before the one that causes the power drop.

3) Get the pilot circuit running. Find the PJ that let's you put the fuel screw between 1.0 and 2.5 turns out. Leave the PJ and fuelscrew alone after that.

4) Set the needle for best midrange power and control. You might need to sacrifice control for power and vice versa. Do not change the MJ to fix a midrange problem. If clip is more than 5 slots down, get a slimmer needle. If the clip 2 or less slots down, get a fatter needle. This may take some effort to find the right top and bottom sizes and taper of the needle. Alternatively, get something like a JD kit that includes a couple of needles and tuning instructions. (I saw that you have a JD kit - I wrote this for a general audience)

5) Solve the off-idle bog by adjusting the AP lever for squirt timing, installing the o-ring mod (pretty much a given), and lengthen the squirt by installing a smaller leak jet (#40 pretty much always works well. I have a #45 on my 450F; it's the one that works for me).

At that point, the carb should be spot-on for the day's riding conditions. When temp or elevation changes a bit, a turn of the fuel screw should solve most idling/starting issues. If the weather changes a lot, pop in 1 size up or down MJ depending if it's colder/lower or hotter/higher outside.

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Hi Jack,

Good questions there. I'll try to answer them well...

Thanks much, Dave. I'll work on the bike all afternoon (bday today, off in the pm!) and report back. Need to pick up some pilots, I think--I have a 45 and 50.

Jack

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My plan (pls chime in!):

1. remove and note the pilot jet

2. determine needle setting and leak jet setting (adjustable)

3. clean, clean, clean the carb and jets

See if I can get it to stall out when I close the a/f screw completely. If not, then lower the pilot jet a couple points and retry.

Then I'll work on the main, which I think may be too fat.

Sound good?

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Answers to your q's:

Hi Jack,

Good questions there. I'll try to answer them well.

Fuel screw all the way in = 1 or 2 PJ sizes too big (rich). Put in a smaller PJ and retest.

If it's popping on accel there are some other questions to ask:

1) does it bog off idle? If so either the needle is in the wrong position or the leak jet is too large or the AP squirt timing is too short (or early or late, or hits the slide, or has insufficient pressure)

>>No, pulls great off idle

2) Does it "pop" on accel. and lacks power or "burble" (like it's drowning in fuel). If popping, your MJ may be too small or clogged and/or your needle is too far down (clip is too close to the slotted end). If it "burbles", the MJ is too big and/or the needle is too far up (clip too far towards the pointy end). Air leaks can make the bike pop on accel. too.

>>has great accel except at the top of the gear. Upshift, and pulls great. Note only done this thru 1st and 2d.

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My plan (pls chime in!):

1. remove and note the pilot jet

2. determine needle setting and leak jet setting (adjustable)

3. clean, clean, clean the carb and jets

See if I can get it to stall out when I close the a/f screw completely. If not, then lower the pilot jet a couple points and retry.

Then I'll work on the main, which I think may be too fat.

Sound good?

Sounds like a plan. I don't bother cleaning fuel jets anymore, I just replace them. A little varnish makes a lot of difference in the jet orifice size and it's just too hard to clean out (imo) without damaging the jet (ala the "don't use a wire to clean your carb" warning).

If the bike pulls great off-idle, the needle, MJ, and LJ are set properly for the midrange and the Pilot Circuit is working (although the PJ is obviously too fat from the <1T fuelscrew position).

If you need to fatten the MJ to improve WOT, you might need to drop the needle 1 clip. Sometimes yes, sometimes no, sometimes you wind up sacrificing one part of the throttle range for another.

Cheers

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thanks. Got frustrated today trying to get the pilot out w/o taking the carb out, then frustrated taking the carb out. So tomorrow I'll try to get an angled driver to get the pilot out, but getting it back in...

JH

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still pretty easy.

put it on the edge of the shorty screwdriver (part of the jet tool if you have one).

Hold the jet on the screwdriver blade and find the hole (pretty far left in the 17mm hole next to the main jet and inside the white plastic baffle). Push it in, then screw it in.

Tada!

No doubt there will be some choice words to be heard. ;-)

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