KTM SX-F engine hesitates, stumbles

mx.david21
Hello all,

I had a scray moment with my 2019 KTM 450, engine hesitated in the air, luckily I could corrigated and avoid huge crash. After landing the bike easily re-start, let's go to the pit, check cables, change air filter, etc.. go back the track.

Problem occured again, but now the bike stop in the exit of corner, engine again easily re-start.

I red some post about problem, fuel filters, tps, rollover, etc.... What can be the potential problem?

Bike has 100 hours, small fuel filter change in every 10 hour, but tank filter has been never changed.

Thank you all the input.
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Paw Paw
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Paw Paw 10/17/2020 4:36pm
10/17/2020 4:36pm
Inspect your fuel pump and filter. It may be time to replace one or both of them.

Paw Paw
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mx317
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mx317 10/17/2020 6:27pm
10/17/2020 6:27pm
Look down in tank and see if fuel is bubbling or appears to be boiling. They have had some in-tank filters cracking and you will lose fuel pressure when this happens. It may only need a filter like Paw Paw said. I had this happen on my Husky.
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milamcreek
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milamcreek 10/17/2020 8:44pm
10/17/2020 8:44pm
Similar problem I have faced, couldn't believe the actual fix. Replace the spark plug, I know it sounds crazy you think I'm getting spark, change the plug. Problem solved.
DynoDan22
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DynoDan22 10/17/2020 9:28pm
10/17/2020 9:28pm
Check upper subframe bolts. The negative grounding relies on the upper subframe bolts being tight. Maybe try a new spark plug as well. Check all electrical connections and, as mentioned, check to see if the fuel is bubbling (bad internal fuel filter)
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The Shop

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mx.david21 10/18/2020 3:28am
10/18/2020 3:28am
Many thanks guys, I have changed the fuel filters, spark plug and test the bike. Now the hesitation was not occured, but FI lamp start to flash, 1x long, 5x short which mean rollover sensor error.

Can the rollover sensor cause that problem randomly?
Lynch
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Lynch 10/18/2020 9:15am
10/18/2020 9:15am
mx.david21 wrote:
Many thanks guys, I have changed the fuel filters, spark plug and test the bike. Now the hesitation was not occured, but FI lamp start to...
Many thanks guys, I have changed the fuel filters, spark plug and test the bike. Now the hesitation was not occured, but FI lamp start to flash, 1x long, 5x short which mean rollover sensor error.

Can the rollover sensor cause that problem randomly?
Yes! My 17 KTM 450 started dying a day before a race and then it happened a bunch of times the first moto. Swapped the rollover sensor with my back up bike and it worked fine after that.
CarlinoJoeVideo
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CarlinoJoeVideo 10/19/2020 9:38am
10/19/2020 9:38am
mx.david21 wrote:
Many thanks guys, I have changed the fuel filters, spark plug and test the bike. Now the hesitation was not occured, but FI lamp start to...
Many thanks guys, I have changed the fuel filters, spark plug and test the bike. Now the hesitation was not occured, but FI lamp start to flash, 1x long, 5x short which mean rollover sensor error.

Can the rollover sensor cause that problem randomly?
These can go bad, maybe it got wet during washing. The race teams have these bypassed, I don't think they are reliable in extreme situations.
trevor129
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trevor129 5/18/2025 8:19pm
5/18/2025 8:19pm

Did you ever figure this out fully? Crashed pretty bad today because of this!

MX558
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MX558 5/19/2025 6:43pm
5/19/2025 6:43pm
mx.david21 wrote:
Many thanks guys, I have changed the fuel filters, spark plug and test the bike. Now the hesitation was not occured, but FI lamp start to...
Many thanks guys, I have changed the fuel filters, spark plug and test the bike. Now the hesitation was not occured, but FI lamp start to flash, 1x long, 5x short which mean rollover sensor error.

Can the rollover sensor cause that problem randomly?
CarlinoJoeVideo wrote:
These can go bad, maybe it got wet during washing. The race teams have these bypassed, I don't think they are reliable in extreme situations.

I have a 25 350 where are these ? Any negatives with getting rid of this ? 

FGR01
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FGR01 5/19/2025 6:52pm
5/19/2025 6:52pm
MX558 wrote:

I have a 25 350 where are these ? Any negatives with getting rid of this ? 

It's purpose is to protect your engine from eating itself without oil pressure if the bike lays on it's side running.   Do you have a stash of spare engines like the factory?  😁

MX558
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MX558 5/19/2025 6:56pm
5/19/2025 6:56pm
MX558 wrote:

I have a 25 350 where are these ? Any negatives with getting rid of this ? 

FGR01 wrote:
It's purpose is to protect your engine from eating itself without oil pressure if the bike lays on it's side running.   Do you have a...

It's purpose is to protect your engine from eating itself without oil pressure if the bike lays on it's side running.   Do you have a stash of spare engines like the factory?  😁

Good point lol

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