17 TC 125 cutting out

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9/17/2018 7:46 AM

I recently purchased a used 2017 TC 125. The bike has 47 hours on it, 10 hours on a new piston and clutch.

It runs great everywhere, but right where it comes into the powerband. I'm not sure how to describe what it's doing, kind of cutting out or bogging. It runs great up to that point and after it. But it you keep the throttle right at that mid position it continues to get worse, add throttle and you're on the pipe and all is good. Replaced spark plug just to rule it out, plug is a light brown after a few laps.

Initially I thought it was the 45 pilot jet that was stock on the 2017. Switched to a 35 to match the 2018 spec, didn't make a difference. It has a 480 main, stock needle and I've been all over the place with the clip position, doesn't seem to cure the problem. With the 45 pilot it would load up in the mid-range, now it seems to run much cleaner but is still cutting out.

Powervalve seems to be functioning as it should and not sticking when revving it on the stand. The powervalve was adjusted to about 4 turns in from full out, changed it to 2 turns. This definitely made the power come on sooner and smoother, but it's still acting up.

Finally I pulled the reeds out. There are some pretty big gaps - could this be the issue? I would have thought reeds would affect the bottom or the top, not the middle but maybe I'm wrong. When I pulled the reed out there was quite a bit of gas in there that came out with them.

Pictures show the reeds sitting on a flashlight. The gaps are twice the thickness of the reed in places.



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9/17/2018 8:43 AM

I would replace the reeds.
I would suspect that the power valves are fluttering.

Paw Paw

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9/17/2018 8:46 AM

Paw Paw 271 wrote:

I would replace the reeds.
I would suspect that the power valves are fluttering.

Paw Paw

Thanks for the reply. What would cause the powervalves to flutter and how would I fix that?

Went ahead and ordered v-force reeds.

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9/17/2018 8:50 AM

You could always flip the reeds as well to see if that doesn't help. Then slap the new ones in when they arrive.

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9/17/2018 9:14 AM

40acres wrote:

You could always flip the reeds as well to see if that doesn't help. Then slap the new ones in when they arrive.

I'll give that a try this week! Thanks.

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9/17/2018 9:52 AM

I'd try the fixes in this order:

1- Replace Reeds
2- Try F1 Power valves arms (Clean and lube power valve assembly)
3- JD Jett Kit

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9/17/2018 10:16 AM

are the F1 arms worth the money?

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vomiting equals disqualification.

9/17/2018 1:34 PM

BR8ES wrote:

are the F1 arms worth the money?

If your power valve arms aren't moving smooth, yes for sure.

My bike was fine with stock arms and with F1, some people notice a night and day difference if they are experiencing problems with OEM.

There's no performance gain besides them helping to make your PV work normal.

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9/17/2018 2:49 PM

BR8ES wrote:

are the F1 arms worth the money?

CarlinoJoeVideo wrote:

If your power valve arms aren't moving smooth, yes for sure.

My bike was fine with stock arms and with F1, some people notice a night and day difference if they are experiencing problems with OEM.

There's no performance gain besides them helping to make your PV work normal.

Thanks Joe, I have some on the way for my 19, thinking I may as well since they are relatively inexpensive.

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vomiting equals disqualification.

9/17/2018 3:49 PM

BR8ES wrote:

are the F1 arms worth the money?

CarlinoJoeVideo wrote:

If your power valve arms aren't moving smooth, yes for sure.

My bike was fine with stock arms and with F1, some people notice a night and day difference if they are experiencing problems with OEM.

There's no performance gain besides them helping to make your PV work normal.

On the stand - revving the bike in neutral the arm definitely isn't a smooth fluid motion, it's more notchy than anything, but it always opens and closes and does not stop at any point. Is that normal or not?

Also if I turn the arm by hand it's very notchy moving it slow and will not always return to full closed on it's own, if I move it fast it's smooth and returns easily. With the bike running it never seems to get hung up.

I'm new to the ktm/husky world, trying to get it all sorted as quickly as possible so thanks for all the help.

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9/17/2018 5:31 PM

BR8ES wrote:

are the F1 arms worth the money?

CarlinoJoeVideo wrote:

If your power valve arms aren't moving smooth, yes for sure.

My bike was fine with stock arms and with F1, some people notice a night and day difference if they are experiencing problems with OEM.

There's no performance gain besides them helping to make your PV work normal.

dtl210 wrote:

On the stand - revving the bike in neutral the arm definitely isn't a smooth fluid motion, it's more notchy than anything, but it always opens and closes and does not stop at any point. Is that normal or not?

Also if I turn the arm by hand it's very notchy moving it slow and will not always return to full closed on it's own, if I move it fast it's smooth and returns easily. With the bike running it never seems to get hung up.

I'm new to the ktm/husky world, trying to get it all sorted as quickly as possible so thanks for all the help.

I cant really move my arms smooth by hand but it rides normal. I've asked a KTM test rider and he said they all feel that way, the pressure is so much that it moves smooth when the bike is running.

The gaps in your reeds are the first thing you need to fix, for sure. They should be sealed.

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9/19/2018 12:19 PM

dtl210 wrote:

I recently purchased a used 2017 TC 125. The bike has 47 hours on it, 10 hours on a new piston and clutch.

It runs great everywhere, but right where it comes into the powerband. I'm not sure how to describe what it's doing, kind of cutting out or bogging. It runs great up to that point and after it. But it you keep the throttle right at that mid position it continues to get worse, add throttle and you're on the pipe and all is good. Replaced spark plug just to rule it out, plug is a light brown after a few laps.

Initially I thought it was the 45 pilot jet that was stock on the 2017. Switched to a 35 to match the 2018 spec, didn't make a difference. It has a 480 main, stock needle and I've been all over the place with the clip position, doesn't seem to cure the problem. With the 45 pilot it would load up in the mid-range, now it seems to run much cleaner but is still cutting out.

Powervalve seems to be functioning as it should and not sticking when revving it on the stand. The powervalve was adjusted to about 4 turns in from full out, changed it to 2 turns. This definitely made the power come on sooner and smoother, but it's still acting up.

Finally I pulled the reeds out. There are some pretty big gaps - could this be the issue? I would have thought reeds would affect the bottom or the top, not the middle but maybe I'm wrong. When I pulled the reed out there was quite a bit of gas in there that came out with them.

Pictures show the reeds sitting on a flashlight. The gaps are twice the thickness of the reed in places.



I have a 18 TC125 model. Mine did same thing..half way accellerating it did a booowahh ...If I kept it screaming pinned it was fine...but accellerating it was horrible and difficult to ride. The problem is your slide cut-a-way is too rich.#4 You can source a 5.5-5.75 from other model bikes,,,75-130 bucks,,,get yours cut by rk for 30,,or grind the opening larger with a dremel tool and sand wheel as I did. The reeds ARE not the problem...everyone thinks this is the taduh moment when they see the gaps,,,I installed different reeds in my 17 TC250, after flat sanding stock cage,, and no real change..Grinding slide on that model gave the same solution..the 18 TC125 changed night and day in smooth excelleration after grinding the opening larger(leaning 1/4-1/2).

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9/19/2018 1:23 PM

dtl210 wrote:

I recently purchased a used 2017 TC 125. The bike has 47 hours on it, 10 hours on a new piston and clutch.

It runs great everywhere, but right where it comes into the powerband. I'm not sure how to describe what it's doing, kind of cutting out or bogging. It runs great up to that point and after it. But it you keep the throttle right at that mid position it continues to get worse, add throttle and you're on the pipe and all is good. Replaced spark plug just to rule it out, plug is a light brown after a few laps.

Initially I thought it was the 45 pilot jet that was stock on the 2017. Switched to a 35 to match the 2018 spec, didn't make a difference. It has a 480 main, stock needle and I've been all over the place with the clip position, doesn't seem to cure the problem. With the 45 pilot it would load up in the mid-range, now it seems to run much cleaner but is still cutting out.

Powervalve seems to be functioning as it should and not sticking when revving it on the stand. The powervalve was adjusted to about 4 turns in from full out, changed it to 2 turns. This definitely made the power come on sooner and smoother, but it's still acting up.

Finally I pulled the reeds out. There are some pretty big gaps - could this be the issue? I would have thought reeds would affect the bottom or the top, not the middle but maybe I'm wrong. When I pulled the reed out there was quite a bit of gas in there that came out with them.

Pictures show the reeds sitting on a flashlight. The gaps are twice the thickness of the reed in places.



riv187 wrote:

I have a 18 TC125 model. Mine did same thing..half way accellerating it did a booowahh ...If I kept it screaming pinned it was fine...but accellerating it was horrible and difficult to ride. The problem is your slide cut-a-way is too rich.#4 You can source a 5.5-5.75 from other model bikes,,,75-130 bucks,,,get yours cut by rk for 30,,or grind the opening larger with a dremel tool and sand wheel as I did. The reeds ARE not the problem...everyone thinks this is the taduh moment when they see the gaps,,,I installed different reeds in my 17 TC250, after flat sanding stock cage,, and no real change..Grinding slide on that model gave the same solution..the 18 TC125 changed night and day in smooth excelleration after grinding the opening larger(leaning 1/4-1/2).

hmm... If the slide is the problem - why does everyone not have the problem? I spent some time at the track listening to other 17/18 ktm or husky's, they sounded waaaay healthier than mine. Spoke with one owner of a 18 ktm125sx, he said jetting was 100% stock and it ran great. Mine's not really even safe to ride.

I'll put the v-force in tonight, fingers crossed that's all I need.

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9/21/2018 7:16 AM

Well, new reed cage and gaskets did nothing. Might run a tiny bit better but it's still not good.

Since the F1 arms have such a long lead time I think I'll clean and polish the stock powervalve and arms tonight and see if that helps. Was really hoping to race this weekend but I'm running out of time!

Added a video so you can hear what it's doing in case there is something else that I should look into. Also went through the electrical connections and checked the mag side crank seal. Don't really want to get into grinding the slide since I don't know what I'm doing there.


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9/21/2018 8:08 AM

You really should sign up at KTM Talk just to view a thread about "Free mods to your carb"... You can easily open the valve cutaway with a chainsaw file and put a small notch on there as well.

You are not the only one who has experienced the VFarce lack of change by the way.

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vomiting equals disqualification.

9/21/2018 9:16 AM

You mentioned the bike ran ok before you did a top end? The garbling I hear reminds me of when I had a customer put a piston in backwards. Not saying you did our the previous owner did, but take the pipe off and shine a flashlight up the exhaust port and take some pics. The sound your bike is making in the video seems mechanically related (piston in backwards or powervalve not opening/closing etc.). I had a '17 with atrocious jetting from the factory and I don't recall mine making that muffled bog. Strange!!

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9/21/2018 9:24 AM

DynoDan22 wrote:

You mentioned the bike ran ok before you did a top end? The garbling I hear reminds me of when I had a customer put a piston in backwards. Not saying you did our the previous owner did, but take the pipe off and shine a flashlight up the exhaust port and take some pics. The sound your bike is making in the video seems mechanically related (piston in backwards or powervalve not opening/closing etc.). I had a '17 with atrocious jetting from the factory and I don't recall mine making that muffled bog. Strange!!

I bought it used, not sure how it ran before the top end was done. Came from a family who takes their kid across the country racing, they had 3 TC 125's. I'm getting real suspicious they sold this one because of how it's running at the moment.

Most people claim the slide affects the off-idle jetting. My issue is mid range. Runs fine off idle and on top, terrible in between.

Here are some pics through the exhaust port.





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9/21/2018 9:34 AM
Edited Date/Time: 9/21/2018 9:38 AM

Once I listened to the video, I am with Dan. Edit- can't tell much from the pix. May have to pull it.

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vomiting equals disqualification.

9/21/2018 10:42 AM

Sounds like the power valve is sticking. I'd pull the arms, look for any notching, clean everything including the rollers. Lube everything up nice. Might have to pull the cylinder to clean it the right way.

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9/21/2018 10:44 AM

Do you have a dealer close by that might have a new set of arms you can try?

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9/21/2018 3:22 PM

So, in the process of cleaning the powervalve. I have a stupid question. Should there be coolant behind the main powervalve cover? The one in front with the exhaust port in it?

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9/21/2018 4:36 PM

No, and that could be the issue as the coolant may be entering the combustion chamber.

Paw Paw

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9/21/2018 5:36 PM

I'm full of stupid questions today. How does coolant get in there? Is it as simple as a gasket or oring or am I looking at a cracked cylinder?

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9/21/2018 5:50 PM
Edited Date/Time: 9/21/2018 5:51 PM

At this point it might be easier to just drain the coolant and pull the top end off. You will get all your answers and be able to clean everything properly.

But I also don't see any coolant in those photos you posted? I'm confused a bit on where you are seeing it.

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9/21/2018 6:05 PM
Edited Date/Time: 9/21/2018 6:36 PM

Coolant is behind the power valve cover on the front of the cylinder. I havent gotten it off yet because it wont come off without pulling the cylinder off and I'm headed out of town. There is no coolant behind the side covers.

When I loosened the 4 bolts on the front cover coolant came leaking out, but now I'm stuck not being able to see inside until I get time to pull the cylinder off. I'm not sure how it's getting in there or being held in there and not going out the pipe. To add to my confusion the coolant is full.

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9/21/2018 6:37 PM

Hey so there is a coolant passage that runs above the power-valve and the front cover does hold it in.
Here's a photo, he's holding it upside down but you can see the port.



With that said, I still think your best case is to drain all the coolant, pull of the head to clean everything, make sure not coolant went into the bottom end. Get those PV arms back in smooth order.
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9/21/2018 6:37 PM

Coolant behind the cover in the pic.

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9/21/2018 6:42 PM

Here’s some before and after photos of when I cleaned mine:




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9/21/2018 6:42 PM

Ahhh... Just saw your pic. That explains it!

So I cleaned the side pieces #11 on the diagram and filed the arms to remove the sharp angle. Power valve moves silky smooth now. I will have to get a base gasket and remove the cylinder to clean everything good.

Now I'm tempted to take it with me to the race...

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9/21/2018 6:53 PM

Could be a compromised o-ring, especially if the PO was into it.

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vomiting equals disqualification.