KXF with SXF internals timing question

mrlongrod
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mrlongrod
Edited Date/Time 4/27/2021 7:33pm
Soo I have 2016 kx250f with a 2015 sxf250 rod, PC cams(Kawi), springs and other small non-timing-related engine mods, such as KTM main bearings etc. The KTM rod is 3.2mm longer than Kawis original, which required 2 extra links added to the cam chain and a cylinder spacer. The best I´ve got it to run was with the IN cam advanced 2 teeth and EX in stock position, but still bogged down on low revs, ripped hard at higher tho. The spark plug is pretty white. I´ve tried all the possible cam positions without the valves hitting the piston, advancing the IN cam 3 teeth seems too close for me to attempt starting it. Advancing the EX cam only made the bogging worse.
Does anyone with more experience have any insight into what I should try next? Maybe press off the IN cam sprocket and have it put back at a few degrees difference? Maybe mess with the ecu tuning?
Thank you!
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Layton
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Layton 4/26/2021 7:00pm
4/26/2021 7:00pm
Where did you come up with that combination of parts?

Better yet, why did you do that?
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Rickyisms
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Rickyisms 4/26/2021 8:33pm
4/26/2021 8:33pm
Layton wrote:
Where did you come up with that combination of parts?

Better yet, why did you do that?
I read this earlier, didn’t reply but thought the same exact thing. I follow moto forums like a bible, and I’ve never heard of something like this.
mrlongrod
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mrlongrod 4/26/2021 10:06pm
4/26/2021 10:06pm
A little update. Advanced the IN timing 3 teeth and runs like a dream now. Has way more top end power with this setup compared to stock.



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Bruce372
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Bruce372 4/26/2021 11:27pm
4/26/2021 11:27pm
Layton wrote:
Where did you come up with that combination of parts?

Better yet, why did you do that?
Rickyisms wrote:
I read this earlier, didn’t reply but thought the same exact thing. I follow moto forums like a bible, and I’ve never heard of something like...
I read this earlier, didn’t reply but thought the same exact thing. I follow moto forums like a bible, and I’ve never heard of something like this.
Ktm 125s have had long for years. It doesn't change the stroke, so CCs the same. The long rod increases dwell time for the piston at TDC.

If nothing else, a long rod is great for a mx forum username lolLaughing
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Polishhammer 4/27/2021 7:54am
4/27/2021 7:54am
The long rod was a big hit with 5liter mustangs back in the 90s. Decrease piston to cylinder load, decrease in cylinder pressure?, and a change in the rod ratio. It’s all a vague memory now.
yzf162
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yzf162 4/27/2021 2:38pm
4/27/2021 2:38pm
You would be surprised what goes into some of these factory bikes. I remember there was a yamaha team back in 06-09 running a almost off the shelf fmf rmz250 exhaust with the mounts relocated on some factory backed yz250f.

Rods are a easy change with way more upside then downside.
Skerby
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Skerby 4/27/2021 3:01pm
4/27/2021 3:01pm
Bravo man. You are a genius for getting this to work, I wouldn't in a million years consider messing with cam timing like that. And then you follow through and actually find a setting that works, goddam legend.
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DynoDan22
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DynoDan22 4/27/2021 7:28pm
4/27/2021 7:28pm
I know a certain Homda 250f team that runs KTM rods. I'm just curious what lobe centers the OP ended up at after adding three teeth to the timing chain and how far off they are compared to what PC spec'd them at. Hats off to you! That's a pretty involved project!
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Rickyisms
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Rickyisms 4/27/2021 7:33pm
4/27/2021 7:33pm
DynoDan22 wrote:
I know a certain Homda 250f team that runs KTM rods. I'm just curious what lobe centers the OP ended up at after adding three teeth...
I know a certain Homda 250f team that runs KTM rods. I'm just curious what lobe centers the OP ended up at after adding three teeth to the timing chain and how far off they are compared to what PC spec'd them at. Hats off to you! That's a pretty involved project!
Phoenix? Their motors sound awesome, I heard their XC2 bike at a spring enduro not too long ago and it didn’t sound like any Honda 250F I’ve heard.
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