KTM 450 SX pilot jet Jump

[FastCletus552]

I got a new to me KTM 450 SX. It didn't run when I got it but I have since got it running. Problem I am having is its a bitch to get started, Especially when its hot. When its bone cold it starts real easy
I've adjusted the valves, and I did a thorough clean on the carb. I noticed the current jets are: Main is a 185, and pilot is 48. Stock settings are 155 main and 40 pilot.
I do trail riding and not motocross so for me I am most interested in easy starts and not super power. I am curious if I drop back down closer to stock would starting be easier? Maybe go from 48, down to 44ish?

Its a FCR 41 carb

 

[byke]

Big main jet. I'd probably put them both back to stock, maybe up one size for colder temps and/or exhaust.

 

[FastCletus552]

Yep. That’s kind of where my head is at. I don’t think any mods have been done. Exhaust is a KTm so assume it’s stock.

 

[Maddevill]

Mine is opposite. Easy to start hot, a bitch to start when cold. I'm thinking of sending the carb to Dave Hopkins. I've got a JD jet kit in mine.

Mad

 

[1962siia]

I'd suggest also checking the accelerator pump diaphragm. They are tough to get right if that is not doing its job. My 05 450exc had a 50 pilot just fyi and ran perfectly when I sold it.

 

[augustiron]

Main jet, starting problems? Huh?

 

[FastCletus552]

Well come to find out I have a compression issue. Whis why the hard start Now the question is Rebuild or Sell?

Took it to dealer and they did a leak down test for me. They said it has 48% compression and anything over 10% is need for rebuild. He also said it was leaking past valves, (whatever that means exactly). The cylinder is relatively new or it looks it, and PO gave me paperwork that it was done, but shop has closed down, and there is no date on invoice. PO has gone dark on me, so don't know when and or how many hours it has on it since top end rebuild.
So I am in question as to what to do that makes the most sense. I am into the bike for lets say $1300 all day. I'm guessing new top end new valves and maybe new bearings will set me back $1000 plus maybe some shop fees. So that means I am into it for now $2300, plus maybe some new tires and odds and ends, so in the end $2500. Only real issue I have with this bike is its a kick start, but the engine has all the fittings for a starter. So maybe if I do a rebuild I can add the starter. I cant seem to find another bike out there that's better for $2500, than what I have. 17yr old bike that's basically brand new internally. What would you do. This is my first KTM.

 

[kxmike]

I bet your valves are tight. Simply shimming them might bring back most of the compression. A bike that old is still gonna need a rebuild though...lower end too.

 

[1962siia]

The rfs motors have tappet adjusters, not shims, for the valves, so valve adjustment is relatively simple to check and do.

 

[Maddevill]

You really need to switch to titanium intake valves on the RFS motor. The stock valves are notorious for sinking in the seats. I have Kibblewhite in mine. Keeping the valve clearance is critical for good running.

Mad

 

[puckles]

check the starter jet size as well. those fcr's have a bunch of little ancillary jets. the pilot seems large which would explain easy cold starting and hard hot starting.

 

[Dmitriy]

You really need to switch to titanium intake valves on the RFS motor. The stock valves are notorious for sinking in the seats. I have Kibblewhite in mine. Keeping the valve clearance is critical for good running.

Mad

I think you mean stock are Ti and KW are SS right?
This thread here seems relevant:
https://advrider.com/f/threads/valve-recommendations-for-rfs-450.936054/

As for dumping money into an old bike only you can decide that.
My 2 cents is that as it’s not a plated bike I would see about selling it and getting something better. Do you ride trail, track, desert?

 

[Maddevill]

Hmmm. Maybe I'm mistaken but I was told that the stock were SS and the Kibblewhite were titanium. Much harder. I guess the valve faces were wearing out on the stock valves.

Mad

 

[OaklandF4i]

Kibble White are stainless.

If the valves have already been adjusted properly as the OP mentioned earlier and its failing the leakdown test as bad the shop says, its time for a fresh motor.

As KXmike pointed out, it may need more than just a top end and valves. Its a very old high performance four stroke race bike with an unknown history. Not unlikely to need a bottom end too.... and if the OP really wants a reliable long term bike, he will need to go through the entire motor to at least inspect. $1k budget to make this motor reliable without labor costs is unrealistic in my experience. Maybe if real lucky...

OP, its rare to find a $1300 running fourstroke MX or Enduro bike, let alone a reliable one. Frankly, this is what I would expect buying such a bike at that price point.

The money spent isnt an investment, you will never get it back. Its maintenance. If you like the bike, have the skills to rebuild it your self, and willing to sink some significant money into it..... keep it and do so. If the answer is no to any of these, then sell it.

If you are honest with the buyer about the motor, its maybe a $500 bike. Perhaps a bit more with a bunch of effort parting it out... but I don't know the market for old KTMs or their parts.