KDX 200 w/RB carb and bogging

[DougBe]

Getting ready to drop kick the KDX. I'm wearing out the carb I've had it off and on so many times. Can't get rid of the bog when I snap the throttle on in 3rd or 4th. 3rd gear roll on is OK, good power, pulls hard. I had a bog before the carb work but I'm focusing on it now. I've had the bike for a year. Was "supposed" to have low hours on a complete rebuild when I bought it. That's all I know about it's history.

Specs: (now) 152/42, CEK-5, 40:1 mix, float level -1mm from mating carb point
I installed Boyeson reeds
RB carb mod w/ long mixture screw about 2 5/16 out.
Stock gearing 13/47. Maybe I should go to 13/49?

I've checked compression. It's consistently 145lbs.
I'm not using any tranny oil, so it doesn't seem like crank seals are bad.
Bought the float tool so I could set float precisely. I have read confusing remarks on float height. I haven't changed this since I set it.
Carb boots are tight.

I'm in the NW, temps are low 40's to low 50's.
Tried every combo of jets from 40/150 to 45/155 and CEK,DEK -3,4,5.
Leaner jets and needle settings made the bog worse.

I've adjusted the mixture screw till I'm blue in the face. Spent hours riding on dirt roads fine tuning it by 1/16 increments +- from 2 1/2 turns out to try to get rid of the bog. Seems the best performance I can get is: the bike will just rip thru the gears, front tire coming up, with me holding on tight, very good lugging too, just walking up hills and then it will accelerate. Sounds great right?
In normal woods riding this would get me by in very good fashion. The only time the bogging shows up is on road riding. I have been trying to dial in the SSS and that's how I noticed the bog. I seem to be in the SSS judging by the roll on and low end performance, but on the road when I stab it in 3rd going up a slight hill it bogs. Someone else said "not like a small engine bog but a BoooWAH bog" if that makes sense. It bogs and eventually when it hits the Kips it takes off.

I appreciate your well thought out responses. This is dead serious to me and the fate of the KDX rests on it. She's shaking in her boots after that comment, :yikes: but seriously this is getting ridiculous. I've never had this much trouble jetting a bike. I'm desperate or I wouldn't be writing this! Maybe this is the best she can be, or there is something mechanically wrong, but judging by what I've read there's room for improvement. Most of you say you have NO hesitation/bogging. This could be due to more mods or not. There are so many posts that are not finished or the info is confused but I thought I would give this a try. I'm sure there's something I haven't tried or left out.


Thanks guys,

Doug

 

[julien_d]

The most simple answer is... use a bit of throttle control Not many 2 strokes enjoy just being thrown to wide open.

Other than that, a "buhhhhWAAAAA" type bog at WOT would normally indicate a lean condition on the main. I'd check really really well for any air leaks around the intake boot, base gasket, and crank seals.

J.

 

[DougBe]

Yeah, thanks J. Believe me I have checked and triple checked everything you mentioned.
I pretty much got this answered on KDXRider, It never was an issue of throttle control, it was an issue of unrealistic expectations. I was reading posts in the RB mod section on KDXrider and guys were going on about how if you wick open your throttle from ANY position you should get NO bogging. I knew better. I took the posts too literally. My bad. The bike performs really well, just like it should. Great low end and lots of power everywhere, you just can't expect to wick her open from lugging to WOT or close to it and not have some bogging.The RB carb mod works very well, big gains in performance everywhere.

Doug

 

[dansavage]

Doug, sounds like you have a nice opportunity on your hands. To be sure I understand, you did get the RB carb modification (with RB's pilot, main, and custom needle), but now you are using the following:

Specs: (now) 152/42, CEK-5, 40:1 mix
And have tried:

I'm in the NW, temps are low 40's to low 50's.
Tried every combo of jets from 40/150 to 45/155 and CEK,DEK -3,4,5.
Leaner jets and needle settings made the bog worse.

I have a 220 w/ a new 35mm carb in it, and it is jetted as follows:
CEL (2nd position from top), 35 pilot, and 152 main (cold) / 150 main (warm 55+F). It took me some time to get here with mine, a lot of fine tuning, but it is on.

The 152 main you are using feels a little lean for your bike. Have you done a WOT plug chop, confirmed leanness isn't a problem then worked down to the needle jet clip position? Maybe I missed this in your detailed post, if that is the case, my apologies.

Also a question on your needle jet position, does 5 mean the bottom position (closest to the needle tip that is submerged into the main jet at rest)? If so, you are pouring her the gas at 2/3-3/4 throttle. I began with mine in the mid clip position and it ran like hell, had to lower it a notch to clean that up. If your running in the 5th, then that would be the next step after the main verification.

Just some thoughts.

 

[julien_d]

Yeah, from your first post it sounded like it was doing what it should. I was wondering if the divider plate in the carb would allow throttle response like that though. It's good to hear your feedback. I plan on looking to RB in the future for carb mods.

J.

 

[DougBe]

Dan- I tried a 155 main with a 40,42 and 45 pilot and each time I cycled through all the needle positions from middle to fourth to fifth heading richer each time because I was thinking it was a lean bog. The richer settings were better but the 155 was too rich. Back to a 152. You can see why I'm wearing out the carb I've had it apart so many times
Yes the -5 position is the lowest, richest position. I worked my way there, the bogging improved as the needle got richer.I'm thinking when it warms up and is less humid (very moist here) I'll have to go leaner on the jets and needle.
You had the opposite experience? Leaner (2nd from top) ran better?

 

[dansavage]

Are you using the RB modified slide or a stock slide? I think they machine the taper (or something) to alter the flow dynamics which results in a leaning of the air/fuel mixture (again, I think). If that is the case, it explains your needle position being lower than mine.

Yes, leaner for me on the needle position worked out best. I netted out at #2 from top, with the air screw turned out 2.25-2.5 turns. When I tuned mine, the 38 pilot didn't work out so well, ended up with a loading problem - putt around a lot with my young son on his bike. I dropped back to the 35 and it works well, nice and crisp at the bottom.

Sounds like you cycled through everything I would have done.

What other mods have you done to your bike?
Pipe?
Airbox Lid?
Good clean air filter?
Good tight spark plug?

 

[DougBe]

Dan-Modified slide and I've done all the mods you mention, including new plug and clean filter. Thanks. Think I'll put this thread and myself to sleep!

 

[sr5bidder]

you mentioned you where lugging it then WOT ....to me its pretty self explainitory. also you said it works great in the woods.

I don't know maybe I just don't understand why on an open road you would not run it up through the gears letting the engine wind out ...if you start in first and rev out 2,3,4, and so on should only be in any particular gear for seconds.

Do you have the torque pipe or the rev pipe or stock pipe??
gearing?

kinda sounds like you don't have the typical kdx200 broad powerband are you sure the kips is not stuck open?

 

[Dixie4]

Man that air screw is turn way to far out, should be 1 1/2 to + or - 1/8 to 1/4 to fine tune, My bog was at 2 turn out did not notice it till on a logging roar as you did, 42 piolet and 1 1/2 turns out 150 main clip in middle, try a different oil and ratio and rejet once you fine it stick to it. All engine seem to have a mind of there own. what works for one guy does not nesseary work for you or me, All mods effects a 2st engine, for every mod I did I had to go leaner and leaner, for what I have now.

 

[julien_d]

Man that air screw is turn way to far out, should be 1 1/2 to + or - 1/8 to 1/4 to fine tune, My bog was at 2 turn out did not notice it till on a logging roar as you did, 42 piolet and 1 1/2 turns out 150 main clip in middle, try a different oil and ratio and rejet once you fine it stick to it. All engine seem to have a mind of there own. what works for one guy does not nesseary work for you or me, All mods effects a 2st engine, for every mod I did I had to go leaner and leaner, for what I have now.

Are you rb'd? The rb users mention a "second sweet spot" on the air screw about 2.5 turns out.


J.

 

[Dixie4]

I talk to Jeff, a few years ago and help me on my set up, He said he try the rb mod and said it was a waist of money that the stock carb was better, once jetted for your type of ride.

 

[DougBe]

I'm RB'd. 2.5 turns out is where you start trying to find the sweet spot (SSS).
I respect Jeff, but a waste of time? Go to KDXRider.net to the RB carb mod section. You see a different opinion there.

I will probably be trying some V-Force reeds. This was a suggestion I got from a couple guys on the KDXRider forum. They aren't fans of the Boyesen reeds on a stock cage. It might take a few weeks for me to try them out but I WILL get back and report.

 

[julien_d]

Yes, everyone knows that Jeff thinks the RB carb mods are a waste of time. However, countless users disagree.

 

[Dixie4]

Well He is the Man that has been racing the KDX line for years and Knows all the ends and outs of the little bike that could, He had to make the switch to the KLX-450, to keep his sponsership so it should not be to long he will find all the little bugs and do the same as the KDX. And on the RB mod no one in the NCHSA on any Brand Bike is useing it, some have tried it But could not tell any difference and came to the same conclusion a waste of money, The big hype now is the auto clucthes.

 

[DougBe]

Here's the update after the VForce2 reeds. I like the reeds, seem to give more bottom end. The bike runs pretty much the same otherwise. No night and day difference. My needle is now a DEK at #4 position.
So, at this point my conclusion is that the bike is running normally.
There could be something mechanically wrong but jetting more isn't going to solve it. I need to ride another KDX or have somebody ride mine to really tell I think. I may all have been a PERCEIVED problem on my part. I've always ridden 4 strokes. This is my first 2T and I haven't had it for very long. 2T's have their advantages in weight and simplicity and 4T's are more forgiving to ride. 2 different beasts. I'm used to a linear power band and that might be the problem. ME!
One thing for sure. The RB carb mod has really added A LOT of power thru the whole band. If you do this mod be careful when you first ride it after you install it. The power caught me by surprise and I looped out. :yikes: The front end wants to walk up pretty FAST now!

 

[Kaw4me]

I talk to Jeff, a few years ago and help me on my set up, He said he try the rb mod and said it was a waist of money that the stock carb was better, once jetted for your type of ride.

Jeff may have a lot of experience but that does not make him an expert in all aspects of a KDX.
Perhaps his riding style or motor tuning didn't make the RB shine but for the far majority of us it's a HUGE IMPROVEMENT.

 

[bikerman]

maybe needle valve is going bad. raise clip 1 notch. hope it helps.

 

[Kaw4me]

Do you think the V-force reed design is that great or is it because their reed cage mounting block is very thick , spacing the carb back
from the intake which will usually show more bottom end response?

Has anyone tryed a spacer plate with a stock cage ?

RB still has a very good product line for a bike that's not been made for almost six years. That's extremely rare in todays market.