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The Bog, the Zip Tie / O-Ring Mod and You

This is a discussion on The Bog, the Zip Tie / O-Ring Mod and You within the Yamaha YFZ450/450R (2004-Present) forums, part of the Performance /Technical category; The Bog: it happens when you stab the throttle from idle and the motor lays over and will die or almost dies. It can happen ...


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Old 01-15-2009, 12:14 PM   #1
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Default The Bog, the Zip Tie / O-Ring Mod and You

The Bog: it happens when you stab the throttle from idle and the motor lays over and will die or almost dies. It can happen in gear or when you are in neutral and usually people will rev the motor up some to get past it.

The Cause: The reason the bog happens is there is a delay in the accelerator pump squirting fuel into the motor when the throttle is snapped open and causes it to go lean and starve for fuel. Now, the reason for the delay is because when they manufactured the carb, they put a weak spring on the accelerator pump arm, so when you stab the throttle, the accelerator pump cam arm and adjuster moves away from the accelerator pump arm and when the reservoir for the accelerator pump is full of gas it can take up to a full second for the arm to move due to the pressure on it and there for will starve the motor for fuel. As soon as the reservoir is empty, they move in unison they way they were designed to do.

The Fix: To cure this, we need to make the arms move together. The way to do this is to zip tie or use a rubber o-ring to hold them together. I prefer to use a zip tie because there is no stretch in it; you choose which way you want to go.

The Instructions:
  • Remove the 2 allen screws that hold on the cover to throttle and accelerator pump. It is on the right side of the bike and the throttle cable goes into it.
  • At this point you will be able to see the arms as well as the throttle wheel. If you can not get in there to do the zip tie or o-ring, then follow the proper procedure to remove the carb from the bike, this is optional because with a little bit of patience you can do this in the bike.
  • Once the cover is off, take your zip tie and start it so that you have a loop and a handle to help maneuver it over the arms, keep the loop big enough to go over the adjustment screw. Try to keep the head of the zip tie towards the bottom as you donít want to have it rub or interfere with the throttle. Get it pulled down tight and cut the excess off.
  • Test the throttle or if you have removed the carb, reinstall the carb and hook up the throttle cable and test
  • Reinstall the cover.
  • Fire the bike up and test while in neutral and there should be no off idle bog.
  • Test ride the bike, if there is still a low end bog, you need to look at your jets.
Note: I borrowed this picture from another forum and in it they used the o-ring, but it still gives you an idea of how to do this what everything looks like. Again you can use either a zip tie or an o-ring.
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Last edited by Hefe; 01-15-2009 at 05:34 PM.
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Old 01-15-2009, 01:17 PM   #2
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Great write-up, thanks!
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Old 01-15-2009, 02:08 PM   #3
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If anyone see's anything I missed or needs to be changed, let me know and I will make them so that the most current info is at the top and easy to find.
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Old 01-15-2009, 04:33 PM   #4
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Quote: Originally Posted by Bowtie View Post
If anyone see's anything I missed or needs to be changed, let me know and I will make them so that the most current info is at the top and easy to find.
this helps great with the bog, but isnt the underlying reason, the reason is because the leak jet is too large, and doesnt allow enough fuel to be squirted in the first place. the leak jet to be moved down to around a 35, it will spray more fuel when the diaphragm is pressed. the zip tie really only helps throttle response more than anything.
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Old 01-15-2009, 04:36 PM   #5
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read this, it might explain a little better, the bog is a problem all across the jetting, dial in the bike, and it will disappear.

http://www.dieseltwitch.com/YFZ450/APTheory.htm
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Old 01-15-2009, 05:35 PM   #6
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great writeup...
stickied!
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Old 01-15-2009, 05:36 PM   #7
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If you take the cover off AP and actually watch it as you go from 0 throttle to WOT you can actually watch the arms separate. I had a horrible bog in mine, and I still have the stock leak jet in it. Before doing the mod, I could kill the motor either in neutral by stabbing it to wide open throttle, or in first gear I would roll the clutch out with little to no throttle, get rolling and stab it and it would die. I made no other changes other than the zip tie, fired it up and had crisp throttle response with no bog. I went to the street and did the same thing and almost flipped the bike, the bog is gone.

I had read that as well and agree that the leak jet can be a part of the cause and that article is right in that when you hammer the throttle, it gets a huge rush of air, and when it doesn't get the fuel to compensate it stumbles and dies. I tend to disagree with the idea that the main jet and needle will help with the bog considering that they only start coming in to play from half throttle to full throttle and the bog happens off idle when the ap arm starts its movement and when you are going past 1/4 to 1/3 throttle the AP has already made it's squirt and is now an open circuit and will only refill once it is closed again. Adjusting the idle up is just masking the problem, just like turning the idle down because you have a vacuum leak and its racing, your not addressing the real issue. Adjusting the timing of the AP arm is what the zip tie is doing, because it is compensating for the weak spring and making it squirt faster and getting the fuel past the slide faster. The leak jet does affect the total shot from the AP and if you still have some bog left after doing this, then restricting what gets bled off may fix it, in my case I did not need to. Then again you may have to adjust the timing of the shot to match the slide position to fully cure it in which case you should refer to the shop manual on how to adjust the timing of it. As soon as I figure out how to make a jpg out of a PDF I can post that page from the manual.

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Last edited by Bowtie; 01-15-2009 at 05:40 PM.
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Old 01-15-2009, 05:53 PM   #8
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every bike is different, depending on location, elevation, mods, etc. im not trying to argue, or even discuss, you seemed to luck out with the zip tie solving your prolem, but the leak is the issue, the other jets are also effected because when your cruising at half throttle and stab it, the pump is still pushed, it doesnt only happen out of idle, it will pump at any point in the rpm range with a sudden burst. the accelerator pump is only for a sudden increase in air velocity to compensate untill vaccuum picks up and starts pulling the gas. the zip tie only makes the burst more accurate with the throttle, is doesnt nessecarily push any more gas, with the wrong leak, any extra gas will just go back into the bowl anyway.

anyway, now im rambling, lol. i was just offering a suggestion for your write up, i think its great and will help people.
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Old 01-15-2009, 06:03 PM   #9
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Like you I always thought the same thing about the AP and that it is always on demand. But one thing to keep in mind is that the arm is controlled by a cam on the throttle blade and the more you open the throttle, the more the arm moves and pushes on the AP diaphragm. Most are designed to be empty by half throttle. A great way to learn about them is to watch a Holley double pumper on a running motor. If you slam it to half throttle you can watch the squirt go in, then hold it there for a second or two and slam it all the way open, nothing comes out. These carbs do basically the same thing. The AP refills it self through the arm releasing pressure and it sucking in fuel as the diaphragm expands.

Like you I am not trying to argue, just trying to get as much info out there so it helps others, and I put in there that if this doesn't cure it, then look to the jets. After reading through others posts in other forums, this has been the cure for it. I will never claim to know it all, or ever come close to that, and I am always reading and learning about these awesome quads!
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Last edited by Bowtie; 01-15-2009 at 06:06 PM.
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Old 01-15-2009, 09:06 PM   #10
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That was a very good right up bowtie.You and level had some very good points.I did the oring mod to mine a couple weeks ago, and now its a comptely differnt machine.Its nice to pull a low rpm wheelie ,and not have to woory about the bog.
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Old 01-15-2009, 10:05 PM   #11
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I am curious about the o-ring, does it flex much? Did you do any tests on it or did you just put the cover back on and go?
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Old 01-15-2009, 11:03 PM   #12
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ive heard the o ring flexes a little too, but i seriously doubt it would be enough to feel, i used hard wire, safety wire for grips, im worried about the constant motion eventually wearing a grove into the plastic peice, but i know of others that have done it too, and no one else has ever noticed an issue.
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Old 01-16-2009, 12:19 AM   #13
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when they are "paired" together, I don't think there is to much movement between the faces, other wise the adjustment screw would wear on the face of the arm, so I would think you are safe with the wire.
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Old 01-16-2009, 09:16 AM   #14
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the oring does flex some but its still 100X better than stock,till the oring slips off ,then i wired it hasnt moved since
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Old 02-16-2009, 06:05 AM   #15
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this is the same mod as for the YZ450F right?
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Old 02-16-2009, 11:04 AM   #16
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If it is the same carb ,then yes.
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Old 09-14-2010, 05:11 PM   #17
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Is this mod also for the 04'? Cuz i give it full throtle and it goes
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Old 09-18-2010, 05:48 PM   #18
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I just bought on 06 yzf 450. It had a ron woods pipe and air intake with a K&N filter. I just put the stock air box back on. (ran terrible) put the Ron Woods intake back on and it still won't run as good as it did before. I seems to run ok in higher rpms, but won't idle and when it shuts off it is hard to start. Any Ideas on what i have done to it?
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Old 10-28-2010, 12:15 AM   #19
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Will this work on an '09?
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Old 10-28-2010, 01:07 PM   #20
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it will on an 09 carbed version, not the fuel injected version. If you have a FI, you will need to get a programmer to adjust out the bog.
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