KTM SXF 450 bogging/low power/decel pop

Grovesy98
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Grovesy98
Hi guys,

I have a 2017.5 Factory edition SXF450 with a minor running issue that's bugging me. It starts fine, but seems to take a while to warm up and clear though. It bogs quite badly until its fully up to race temperature. On the track it feels quite sluggish, like it's down a few horsepower from where it should be. The response isn't crisp, slightly delayed, and I get a lot of decel popping. It doesn't stall or misfire.

So far I've done the following -

New plug
Checked valve clearances are in spec
New inline fuel filter
New clutch
Fresh fuel

Its going into my local shop this week to have a dyno and diagnostic run to investigate, so hopefully will know more soon, but I'm thinking along the lines of fuel pump filter blocked, partially blocked injector, or possibly tps?

Anyone had similar issues and resolved it?

Thanks
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Digger29
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Digger29 2/14/2022 12:54pm
2/14/2022 12:54pm
I would lean towards the TPS but those yrs also had a number of them end up with the gas line in the tank getting kinked. I've seen it a number of times.
Grovesy98
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Grovesy98 2/14/2022 2:10pm
2/14/2022 2:10pm
Thanks, yeh I've seen that can be a problem from searching online. If the dyno points to a fueling issue then the pump needs to come out I think, change the filters and check the fuel lines
mx317
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mx317 2/15/2022 7:07am
2/15/2022 7:07am
Also look in the tank when it is running and see if the gas is bubbling. I had one that had the in-tank filter cracked and was losing fuel pressure due to that.
stone881
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stone881 2/15/2022 8:48am
2/15/2022 8:48am
Another thing to check is the spark plug cap. They can crack internally and cause some strange issues.

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Grovesy98
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Grovesy98 2/15/2022 9:11am
2/15/2022 9:11am
Thanks guys. Dropped the bike to the shop today. They are going to do a leak down test first to check the piston and rings, and valves. If that checks out ok then it will go on the dyno for further checks. The bike has a total of 86 hrs now, and 36 hrs on the current piston, so could probably do with a new one anyway, along with the cam chain
Grovesy98
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Grovesy98 2/18/2022 10:48am
2/18/2022 10:48am
Update, bike is all sorted now. Turned out to be the fuel pump was faulty, and there was also evidence of sand in the tank somehow. I'm always careful when filling the tank to make sure its clean first, so not sure how it's happened, or whether it was the main reason for the failure or not. Anyway it's been tuned on the dyno and with the new fuel pump makes the correct power now. The leak down test showed the top end to be in excellent condition and does not need rebuilding for a while yet
mx317
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mx317 2/18/2022 12:19pm
2/18/2022 12:19pm Edited Date/Time 2/18/2022 12:21pm
Grovesy98 wrote:
Update, bike is all sorted now. Turned out to be the fuel pump was faulty, and there was also evidence of sand in the tank somehow...
Update, bike is all sorted now. Turned out to be the fuel pump was faulty, and there was also evidence of sand in the tank somehow. I'm always careful when filling the tank to make sure its clean first, so not sure how it's happened, or whether it was the main reason for the failure or not. Anyway it's been tuned on the dyno and with the new fuel pump makes the correct power now. The leak down test showed the top end to be in excellent condition and does not need rebuilding for a while yet
I hope they checked the in-tank filter. It will test the same as a bad fuel pump if it's cracked because both show low pressure. The ones that are cracking are made in Turkey and the better ones are made in Austria or Germany. They are all Mahle brand.

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