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Hello, I have a 2014 kx100 that I recently installed a JD jet kit on. The JD jet kit solved all of my issues except the bog I have when the throttle is wacked wide open. I think it's lean on the pilot jet because it feels flat off idle and my airscrew is barley half a turn out and still feels too lean on the pilot.

 

It has a 145 main jet with the blue (richer) needle on the 3rd clip position and a 45 pilot jet. The pilot jet is the only thing the JD jet kit didn't change and the bog is the only issue I have left with the bike. So that's why I'm thinking the pilot jet is the culprit. If I wack the throttle wide open it'll bog then rev out as it should, just a bwooogg sound. Same thing happens when I'm riding and pull in the clutch and wack the throttle open, bwooogg.

 

Only aftermarket things on the bike is an FMF factory fatty with the Powercore 2 silencer. I just want some opinions before order some more brass off Rocky Mountain ATV. The bike runs great in the power and but just has that nasty bog. Thanks.

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Literally running into the same issue as you at the exact moment. My JD Kit came with a 45 pilot which I put in. (Replacing a 48 which was in there) I get the same bog when cracking the throttle. I’m going to throw the 48 back pilot in and I’ll report back. Strange no issues with bog on the old jets and needle.

 

 

Oh and similar mods as you have.

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Literally running into the same issue as you at the exact moment. My JD Kit came with a 45 pilot which I put in. (Replacing a 48 which was in there) I get the same bog when cracking the throttle. I’m going to throw the 48 back pilot in and I’ll report back. Strange no issues with bog on the old jets and needle.

 

 

Oh and similar mods as you have.

Strange, must be the pilot jet! But will be looking forward to hearing from you. I was quite disappointed that the JD kit didn't come with a couple different pilot jets. I ordered it for my 02 cr125 I had last year and I got lucky that the pilot that came with it was the right size.

 

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Strange, must be the pilot jet! But will be looking forward to hearing from you. I was quite disappointed that the JD kit didn't come with a couple different pilot jets. I ordered it for my 02 cr125 I had last year and I got lucky that the pilot that came with it was the right size.  


Kinda stumped. I really don’t think it’s a lean bog, it doesn’t cut out. I don’t think the pilot is the issue. I put in the larger pilot and it’s the same. I put in the old needle main and pilot and it runs way better. I’m at 7000+ feet, and am currently running 48/130 I bought the JD thinking it would just clean things up slightly through 1/2-full throttle.

Does yours completely cut out when you crack it all the way open? Mine basically kinda goes bwawawAhwahwah and never dies.

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Posted (edited)

Before messing with the jetting any more, I'd

Confirm there are no air leaks and, closely inspect the reeds for any damage or gaps.

Make sure the carburetor's float is set to factory specs.

Inspect the throttle slide for any damage/cracks that would increase the cutaway's effective height.

 

EDIT:  a failed power valve in the 'open' position would also contribute to poor low end/throttle response.

(happened to me once on my YZ125)

Edited by mlatour

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Before messing with the jetting any more, I'd

Confirm there are no air leaks and, closely inspect the reeds for any damage or gaps.

Make sure the carburetor's float is set to factory specs.

Inspect the throttle slide for any damage/cracks that would increase the cutaway's effective height.

 

EDIT:  a failed power valve in the 'open' position would also contribute to poor low end/throttle response.

(happened to me once on my YZ125)

 

Thanks for the advice! I do indeed have some gap on the sides of of the reed petals, specifically on the middle sets. I suppose this is not normal. Ill check the other things tomorrow. Thanks

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No air leaks or anything, reeds look brand new on my bike. But I do that the same problem as him, if the throttle is wide open in neutral it just goes bwahbwahbwahbwah and sounds horrible. After doing that for a couple seconds it revs out.

Before messing with the jetting any more, I'd
Confirm there are no air leaks and, closely inspect the reeds for any damage or gaps.
Make sure the carburetor's float is set to factory specs.
Inspect the throttle slide for any damage/cracks that would increase the cutaway's effective height.
 
EDIT:  a failed power valve in the 'open' position would also contribute to poor low end/throttle response.
(happened to me once on my YZ125)

Yes! Mine does the same thing, the bwahbwahbwahbwah



Kinda stumped. I really don’t think it’s a lean bog, it doesn’t cut out. I don’t think the pilot is the issue. I put in the larger pilot and it’s the same. I put in the old needle main and pilot and it runs way better. I’m at 7000+ feet, and am currently running 48/130 I bought the JD thinking it would just clean things up slightly through 1/2-full throttle.

Does yours completely cut out when you crack it all the way open? Mine basically kinda goes bwawawAhwahwah and never dies.

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I just think my pilot is too lean since my air screw is less than half a turn out, if I turn it out to 1 turn it has a bad lean bwooogg sound when trying to blip the throttle. But as for the bwawawawawa sound when the throttle is held wide open I have no idea, I do have a bit of spooge that drips down my silencer as well.

 Maybe I'll take a video of it and post it to YouTube so you guys can hear it.

 

 

 

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Transitional fueling is handled by the needle.  The pilot circuit operates on vacuum which disappears as soon as you open the throttle.

If you go rich enough on the pilot that it loads the motor up with fuel it will no longer bog but it will be very rich at low throttle positions and generally run like shit. 

To some extent it is normal for a small bore engine to bog if the throttle is opened too far too quickly at low RPM.  This is not a matter of jetting.  Once the throttle is opened a certain amount the vacuum on the engine side of the carb disappears which cuts off fuel delivered from the pilot circuit.  If the engine isn't moving enough air to maintain a minimum amount of flow through the carb bore there will be no fuel drawn through the main jet circuit either and the engine will bog. 

This is a non issue on big bores, they have a strong enough intake signal and much smaller carb relative to their displacement to handle any amount of throttle anywhere above idle.  125's and smaller engines will have this tendency to some extent no matter what you do.

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Here's what my bike is doing. The bog is affecting the riding, sometimes when I slip the clutch on a corner it bogs a bit.

 

 

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If you have a habit of letting the throttle snap shut, inspect your throttle slide for damage.

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If you have a habit of letting the throttle snap shut, inspect your throttle slide for damage.
I don't usually do that, slide is in great shape. Might try the #3 slide.
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It would be great for any help I bought a kx80 1993 model it has spark and compression I drained gear box oil and noticed metal in oil after taking off clutch coverthere's a bit snapped IL attach a picture any info would be great I'm unsure if this would be what's causing it not to start

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It would be great for any help I bought a kx80 1993 model it has spark and compression I drained gear box oil and noticed metal in oil after taking off clutch coverthere's a bit snapped IL attach a picture any info would be great I'm unsure if this would be what's causing it not to start
I would recommend starting a new thread for your topic but I'll give you some tips. If there is a lot of metal in the tranny/clutch area lots of damage and wear could have occurred to the bearings, gears and other components. You will most likely have to split the cases to get all the metal out and ensure nothing has been damaged. I had a 1988 cr125 that had a worn case so bad the clutch basket was hitting the crack case and it had metal all over in the tranny and needed all new bearings etc because of that. But I'm not sure if that's causing it not to start. Did you compression check it with an actual compression tester? Hand testing is not a way to test for compression. A motor needs air, fuel and spark along with proper compression to run. If you don't have one of those it won't run. But in your case before any of that your gonna have to get the metal out first before you try and start it. And again I'd recommend starting a new thread.

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Drop the clip on the needle using the washer he gave in 1/2 clip increments. Pilot circuit will address throttle response but pretty much gets lost when that slide goes up. Either a: the jd is too lean of a diameter or b: you need to richen your needle a half clip. The needle is pretty much everything except just off idle and wide open. If the pilot is lean then with bike at operating temps it would surge at idle in gear or have a hang just before idle after revving. You are both describing a lean needle.

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Ok thanks for your info.

Drop the clip on the needle using the washer he gave in 1/2 clip increments. Pilot circuit will address throttle response but pretty much gets lost when that slide goes up. Either a: the jd is too lean of a diameter or b: you need to richen your needle a half clip. The needle is pretty much everything except just off idle and wide open. If the pilot is lean then with bike at operating temps it would surge at idle in gear or have a hang just before idle after revving. You are both describing a lean needle.

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So I richened my richest needle I have out and still the bog is there, no change. I will say I was able to have my airscrew farther out than before, I'm at a little more than 1 turn out (maybe 1 and an 1/8th turns out) but the bog is pretty bad like it was, I know these little motors don't have a lot of velocity to suck fuel out of the carb to meet the demands of the throttle being wacked open but I owned a 06 yz85 a little over 5 years ago and a 2002 cr125 and they ran great. The cr125 had a JD jet kit and the yz85 didn't. I never had a bog like this bike has. I could wack the throttle open all I wanted on those bikes and they never hesitated. They were jetted perfectly too.

 

That's why I just don't know why this bike has it, for the fact that the kx100 and yz85 have similar carbs and this bike is 100cc and the YZ was only 85cc with no bogging issues. I mean it could be the slide is too lean I suppose, but if I turn the airscrew any farther out to let's say 1.5 turns, it starts to have a small hanging idle, another pointer that the pilot is too lean.

 

So as of right now my jetting is:

- 145 main jet

 

- JD jetting Blue needle at the 2nd (richer) position

 

- 45 pilot jet

 

Im probably going to order a 48 and a 50 pilot jet for it and see what happens.

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It was mentioned earlier but do the reeds have any air gaps, chipped edges/corner or other visible damage?

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