Just bit the bullet on some "Bog" parts.

So I've been trying to get rid of the infamous bog and just can't shake it. I have the JD jet kit, the bike totally rips everywhere, pulls like a freight train, its just that quick snap of the throttle when you want to loft the front tire up over an obstacle in the low rpms, it falls on its face. After doing the O-ring, setting up the AP timing screw to just miss the slide, installing a #45 leak jet, I still have the bog. I even went for ride after ride messing with the AP timing screw and slowly turning it different directions all throughout the spectrum and the bog doesn't go away. So after hearing a lot of good things on the R&D products, I decided to get the new and improved R&D Power Pump 2 with the adjustable leak jet located on the left side, and a heavy duty linkage spring along with the block off screw for the leak jet in the bowl. I hope this will cure my bog!

Funny thing is, I completely got rid of the bog on my YFZ450 with a #35 leak jet and a Boyesen Quickshot 2, and Zip-tying the linkage. But I decided to go a different route this time, instead of continually removing the bowl to try different leak jets.

Once I get this all installed I will give some feedback on it, I sure hope it works!

I blocked my leak jet with good results.

i have the same issue. I would love to know if that works, seems so easy to adjust the leak jet on the outside. Does anyone know if it will fit my 00' carb that does not have a leak jet?

You would think it would if the accelerator pump cover is the same as the newer carbs. The kit has you block off the leakjet in the bowl so I wouldn't think it would be a problem.

You block off the leak jet in the bowl because the new cover has a screw that replaces the function of the leak jet. All the covers do is enable a quick change of leak jet size by simply turning a screw Vs. pulling the float bowl, swapping a jet and putting the bowl back on.

To the OP, if you still have a bog after all you have done, there is something else wrong. I assume you mean you have the bog while riding and not simply nailing the throttle from a flat idle while standing still.

If your carb does not have a leak jet, adding a cover is a total waste of money.

You block off the leak jet in the bowl because the new cover has a screw that replaces the function of the leak jet. All the covers do is enable a quick change of leak jet size by simply turning a screw Vs. pulling the float bowl, swapping a jet and putting the bowl back on.

To the OP, if you still have a bog after all you have done, there is something else wrong. I assume you mean you have the bog while riding and not simply nailing the throttle from a flat idle while standing still.

If your carb does not have a leak jet, adding a cover is a total waste of money.

Haha, yeah the bog is while riding. I baby the engine while not riding. I'm not a "campground rider" as I like to call them. Trying to relax at your campsite , usually while you're asleep at night, and someone always cranks up their cold engine and revs it wide open a few times, makes a couple circles around the campground, and shuts it back off, and repeats this throughout the night. :excuseme:

I chose the R&D cover because it appears to do the same thing as the Boyesen Quickshot 2, plus has an adjustable leak jet, and comes with the stiffer linkage spring, and call me looney, or maybe it was just a placebo affect, but the Boyesen Quickshot 2 made my YFZ much more responsive and snappy and almost did away with the bog. I then installed a #35 leak jet, but it wasn't till I zip-ty'd the AP linkage(the o-ring didn't help much) that the bog completely went away.

I also had the bog on my KTM 525, and couldn't get it to go away till I swapped the diaphragm for a JD honda one I think it was.

So, we'll see how it goes I guess, I hope this is the trick, if not, it might be like you said and something else.


I had to ask where you test as nearly any bike, no matter how perfectly jetted, can be made to bog 'on the stand'. The issue must only occur during actual, normal riding to justfy rectification.

All of the covers (R&D, Boysen and Merge) more or less do the same thing in avoiding sucking air. The R&D and Merge have the ALJ. The differences are the adjusting screw is on the left on the Merge and they both manage in intake of fuel slightly differently.

You want to be careful locking the AP linkage together. If the diaphram bottoms and more force is applied, parts can break.

I suspect you need to play more with the timing screw if a 35 lj was needed. I have never seen any bike need even a 40, and those that had them, had steady throttle driveablity issues.

The stiffer spring is a better solution than the oring.

Okay, so I finally got everything on and took it for a test spin. The bike was exactly the same! Bog still there did nothing. I tweaked with the adjustable leak jet all the way through the range until I turned blue in the face and I couldn't get rid of the bog. Set the AP timing again, made sure it was perfect, and still the bog. I kept messing with the AP timing, leak jet settings, and even the fuel screw and jetting and nothing helped. So I finally decided to Zip-ty the linkage like I did on the YFZ and adjusted the leak jet way down to 20 and lower, and the bog is all but gone. The only time it bogs is when you are really lugging the engine in super low rpms and snap the throttle, and its just a slight bog. I even put the heavy duty spring that came with the kit in and that did nothing, and yes I have everything installed right, I checked, and re-checked. The funny thing is, I tried zip-tying the linkage before, with no powerpump, and it didn't help, but now with the powerpump it works.

So, since I've heard from a few people that Zip-tying, or safety wiring the linkage together can bind parts and be hard on the diaphragm, is there anything I should do, like put a different diaphragm in to keep it from binding?

Thanks again.

I have a 05 WR450. You don't mention what piolt jet you are running. Or what the setting on your fuel screw is. You may want to go richer on your piolt and play with some adjustments on your fuel screw. I ride from 5 to 9000' My main is a #165 or #168. JD Blue Needle Mid position. I run a #48 pilot 2 turns out on the screw and a #40 Leak. Once warmed up my bike will come over on you if snap the gas. I found the O-ring trick on the AP linkage to give to big of a shot for my bike and it makes it kinda choppy when I gas it.

Right now I have a 45 pilot jet, it seems to like it at 1 1/2 turns out on the fuel screw, 165 main, JD Red Needle 4th from top. I ride from 5000 feet up to 10k+ feet.

Fuel screw is for idle only. Jetting (needle, main) is for basic running.

AP is for a bog. Messing with the basic jetting to cure a bog will only make your bike a nightmare.

Being when you 'hardwired' the AP cam, the bog seemed to go away tells me something is not functioning properly. Most likely the check valve is leaking or the diaphragm is bad or the diaphragm spring is in wrong.

The R&D power pump has you remove the check valve completely. The diaphragm looks great, and the spring is installed correctly.

As for the jetting, I took some recommendations from James Dean, it was only a last resort move just to cross that off the list.

I just went out for a nice trail ride and the bike is running awesome. I've got the ALJ set at about 30 and the linkage still zip-tied. The only time you can get it to bog is in real low rpms when you snap it, and it's only every once in awhile, but when it does it it doesn't fall flat on its face and almost throw you over the bars anymore. I guess some of this is just normal when your lugging it anyway. I'm usually in a lower gear and in the upper RPMs when I snap the throttle to get the front tire up over something, where lately I've just been trying to make it bog everywhere. Maybe OCD is getting to me. :doh:

Unless you check and confirm the AP diaphragm is not bottoming, you run the risk of bending or breaking on of the parts.

If you are really lugging the engine, you should either cdownshift or consider different gearing. Lugging is very bad for the engine.

There is a check valve in the R&D unit. You have the tiny oring in?

Yup, tiny O-ring is in.

I'm not lugging the engine to where it's rattling your teeth and about to cut off, I'm just down in the low rpms, you might consider cruising speed, in a higher gear to keep your rpms down, and then snapping the throttle, for "experimental" purposes only, just to try and induce a bog. This is where the bog exist.



In zip-tying the linkage you have essentially done the Red Beard mod EXCEPT you need to grind down the diaphram stud so it doesn't bind when ample throttle is applied. I found my 06 WR450 to run the best with the Red Beard mod also but I had best results with an 80 leak jet (I didn't have an R&D bowl).

I've been reading endless pages on this red beard mod on the CRF forum and it is some very interesting reading.

Since I seem to get the best results from this type of mod, I found the Rapid Response linkage by Ready Racing on ebay for a few bucks and ordered it. It's suppose to directly connect everything like the wires and zip-ties, but you don't have to worry about it failing and jamming up in there.

As for the diaphragm, I bought one before years ago for my KTM, I believe it was a Honda diaphragm, but it had the much shorter post. Does anyone know what diaphragm, part number perhaps, that has the much shorter post? I would rather not grind down my stock one in case I need to go back to stock.

I wonder though if the R&D power pump, and Quickshot have more space in the chamber to keep the diaphragm post from bottoming out, like it would on the stock AP cover?


One caveat of the diaphram used in these carbs is the variation of fuel pumped via a new diaphram compared to a used one. I found there to be a big decrease as they age. I wish they could have used a positive displacement plunger like a piston-cylinder setup instead of a flexible diaphram. Oh well, it won't matter long anyway with the advent of EFI.

Yeah this bog has had me so irritated, I was about to sell the thing and go get a CRF450 EFI, haha. Shame on me.

I took the zip-ty off today from both bikes, the WR and the YFZ, and the bog is back, just like that, put the o-ring on and still have the bog.

Anyhow I found the diaphragm with the shorter post and went ahead and ordered it, I'm going to try that with the new Rapid Response linkage. I'll probably have to go way up on the Leak jet being that I'll be using such a short post on the diaphragm, but hopefully my adjustable leak jet will come in handy then!

I have a suggestion. When i was setting up my stock carb, i would leave the fuel line attached and let fuel fill up the float bowl like normal. While aiming the carb in a safe direction, i could give the throttle a quick opening and see the accelerator pump doing its job.

At first, the stream was very weak, like it had a swollen prostate.

Then, after tweaking the AP spring, and grinding the ap diaphragm rivet, the stream became very powerful and could shoot 6 feet.

I would recommend this visual procedure, as bolting it all back together and riding it just isn't time effecient.


I almost want to say go to a #42 PJ and open the FS a bit.

I'd avoid running the pilot circuit rich in order to tune-out a bog. That just makes the bike unresponsive.

How are you checking the AP timing? With a video camera or your eyeball? It's pretty hard to see the AP squirt barely miss the slide if you eyeball it. Also, if you haven't cured the bog with a #40 LJ (or equivalent) something else is wrong. The #45 that I'm currently using just barely starts loading up the bike on woops; I'm close to trying a #50 and seeing if I can get away with the slightly shorter squirt.

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