125-200cc Finally, no more bog

Today, I was able to finally tune the bog out of my wife's WR125. After being inspired by Walt, I opened up the powervalve. I tried a cheapo spring from Ace. While this did not cure the bog, it was fun to have a wheelie-popping hit when the PV opened.

So, the next thing I did was raise the needle to the 5 clip from the top (as high as it can go). Then I ground the ends of the origional powervalve spring a bit. Lastly, when I put the linkage for the powervalve back together I pushed the adjuster screw on the linkage as far up as possible. My thoughts on this is that the PV will open just a bit sooner, or even stay open just a bit.

I took the bike out today and it ran perfectly. No bog. Really, really strong on bottom. It will pull in 6th gear from almost a chug until the PV opens.

Since i am a novice at jetting, nonetheless, PV stuff. I have to think the problem is as Walt described: the PV sealing too tight. I think grinding it, or figuring out a way to have it slightly open helps the bike run better. Just my thoughts.

JS

Hey good job and thanks to Walt for sharing with us. I will be getting a sprig and grinding info from Walt as soon as I send off and get my EG144 kit back and installed. I don't have a bog with my Cr but I want as much bottom and mid as I can get.

It would be interesting to see what happens if you put the needle back where it was. the dreaded bog could be jetting related. Some throttle positions are hard to dial in if you don't have needle options.

If it still runs good in the original needle postion then we know it is power valve related.

That is a good point. I did move the needle to the 5th clip yesterday when I had the ACE hardware spring in the powervalve. The bog was better, but still very noticable.

One thing I did not mention, is the temps have dropped her in Hollister, CA this past week. The bog got worse as the temps dropped...suggesting a jetting issue right? Since we had the bike it always seemed to run best when hot...after 40 minutes of riding and as the temps got hotter.

Today when I took it out, it warmed up quickly, even though it was cold. But today, the bike ran the best it ever has. Absolutely no bog and a much better pull from closed PV to open. In fact, I was able to ride longer in one gear, pulling hills and coming off of large whoops without having to down shift. I spent most of the time riding with the PV closed, instead of having to kick down a gear and rev it up. It made the bike much more enjoyable to ride. I really tried to find the bog today and could not. I put it in 6th gear and rolled on the throttle and no bog. The bike pulled from closed PV to open PV on an incline (would not do this before).

So, I have no idea if it is a jetting issue or not. We will see what happens when the temps warm. I may have to drop back to the 4th clip. I would be curious to know what happened if someone with the bog tied the PV open...if the bog was still there or not. When I first got the bike the needle was in the 3rd clip and the bike had a huge bog. I dropped it to the 4th and the bog improved significantly.

Anyone try a different needle for this bike?

JS

Also, if only someone had the time to hook the bike up to a dyno and A/F sensor to see what is happening at the point of bog.

JS

Does the bog happen at a certain throttle position, or instead more of a certain rpm?

A tied power valve would be a good test. There would not be much low end but the bike still should not bog if jetted right. Or maybe it is a different kind of bog then I am thinking of. I am thinking of the kind where at the worst it feels like the bike just ran out of gas and at the best it is just really weak and needs tons of clutch to get moving. On my 06 these are the kinds of bogs I have experienced and they have all been jetting related. the bike is picky and I relly had to play with needles to get it as good as it is now. But I have a keihin so I have plenty of needle options to play with.

Keep up the good work jsleeper. I could modulate the throttle all over the place in my bog and it had no effect. I also had no problem making the needle too lean to too rich and certainly when it was at the right mixture the bog was less but still significant. I don't remember anyone having this severe a problem with a bog in any of the pre-09 125's. The ones that had carburation issues were able to change out to a pwk or at least use a power now to eliminate the issue. I had all kinds of issues making the old TMX idle at altitude and was able to fix my problems by switching out with a PWK. The switch didn't work with this problem. The new TMX is much better although the lack of needle selection is irritating.

I would love to have a shop with a dyno and all the cool test equipment. Without it though I am forced to just treat the symptoms by doing just what JS said and keep the pv slightly open in the bog zone. I think for the percentage of 125's that can't seem to solve the bog the spring kit should eliminate the issue. For everyone else with a 125 it will at least make the pv open more progressively.

Walt

So do you think there is a quality control issue with the power valve spring? Everyone isn't having this problem so perhaps a few people got still springs? Either way it's great that you are getting this problem figured out for the rest of us.

Don't overlook the air screw on the Mikuni carb. It s a very sensitive, but tunable carb. I found the carb range to be less than 20F before needing an air screw setting change.

When you say you adjusted the screw all the way up, are you talking about in the slotted bell crank? Did you go just a little, or all the way? I may try this, mine is so lean on the bottom, it dies when you whack the throttle open. The only way I can get it to run is with a drilled pilot. I found low compression, so I am putting in a ring now.
GP

Hi, not sure how to explain which screw it is, but with cover off for the PV linkage, there are two screws/bolts (8mm). The bolt to the right attaches the linkage together, but the linkage is slotted. Mine was adjusted to the bolt was at the bottom of the slot. I pushed the linkage all the way down, so the bolt was at the top of the slot. Presumably, opening the PV a little more/at a little earlier RPM.

JS

Do any of these PV issues apply to the WR250? I've had the chance to ride 2 different WR250's and haven't noticed anything...but I'm a rookie tuner.

My WR 250 was great and I had no issues with it. I think the 125 has such a large difference in pull between open and closed that it exacerbates any issues with progressiveness. My 125 didn't open until at least 8000 rpm stock and made an already mid-bog situation even worse. My recommended spring combination for woods riding has the pv partially opening at ~5000 rpm and then fully opens at ~7000 rpm. I have a laser tach I will be hooking up to it to really pin point openings when I get my rad back from Myler's. Much easier to ride in the tight stuff with that progressive opening.

Walt

Adjusting the power valve linkage from the middle to the top of the slot fixed the bog on my friend Shane's WR125. I adjusted it before our ride yesterday and it runs near perfect.

Here is a video where I am riding the 125 on yesterdays ride.



Later,

What's with all the brown stuff? And there's giant fly on the lens!

That was a kicka** vid.

Wow that was a great video and that 125 sure sounds crisp. Thanks for sharing.

Yes, Shane's 125 sounds way better in that video than it did in the last one he was in. So seeing as the springs that were supposed to be delivered today didn't show up, I spent the afternoon working with the power valve adjustment to find out what was happening. I didn't mess with it before because the more you adjust it the less it opens fully. What is happening is that by adjusting the screw up it is pre-loading and creating a larger gap in the ramp cup that the balls work against to open the governor. This allows the balls to start farther from the center creating a larger centrifugal force and reducing the rpm needed to open the power valve. It doesn't effect anything else about the action so the pv's open the same way just sooner and not quite as far.

With the linkage adjusted all the way to the top, it is opening the pv almost 2000 rpm sooner, but total opening is only about 60%. While there is enough range of motion in the governor to allow it to open fully the ramp angles in the cups do not allow the balls to open the governor to its complete range. The earlier opening is doing exactly what the springs do and allow the flat spot to be eliminated. I would say that the power valves not opening fully probably don't affect hp until 9000+ rpm. So I worked with the adjustment to find where the happy medium was. With the bolt adjusted 1/3 of the way to the top you still had full range of pv movement and it lowered the initial opening by about 1000 rpm. At 1/2 the way up the pv's still opened about 80-90% and it lowered the opening rpm by about 1500 rpm. After more than 1/2 open there is a diminishing return as I could feel the loss on the very top. But the tighter the woods the less this is going to be an issue.

I love this stuff. The springs give you another option and the inner springs allow you to make the opening more progressive, but this is certainly an option that works.

Walt

Thanks Walt, Kelly and I have been talking back and forth trying to figure out if it opens sooner my moving it to the top or later.

I was on your side,

Shanes was set at 2/3 from the bottom when I adjusted it, the last 1/3 made all the difference in the world.

Later,

Jake,

You could hear that it was opening the pv well before the bog I had heard on an earlier video. Even opening only 60% or so it still pulls hard for that 3000 rpm until you start losing on top. With the CR tranny it only drops it about 2000-3000 rpm anyway so if it pulls that well from 6000 on up to 9000 why worry about the top end.

One thing that kind of confirms what I was thinking is the lighter the spring the less it drops the opening rpm. Because it isn't a direct 1:1 relationship and actually works on a substantial curve the earlier on the curve your opening rpm is the less it changes on the vertical axis with changes to distance from the center shaft. I just re-read this paragraph and it makes so little sense I am roflmao. I know what I mean.

I will do more tomorrow with the laser tach and get some real #'s with the different springs and it will all become clear as mud. I was just using the spark plug mini-tach today and it is accurate as measuring water depth with a floating fly line and no weight.

Walt