2 stroke tuning.

[Nebuchernezzer]

Howdy, I'm newish here. I'm one of Fimp's mates :). Anyways i just rebuilt a bike I bought recently so i have some questions about tuning it if anyone knows.

I picked up a 1997 KTM EXC 250 off a mate for $500, it was in need of a top end rebuild which I did a few weeks ago. Now that it's all back together I'm looking at making it run nicely.

So far with the factory settings (jet sizes etc all taken from the KTM workshop manual) it runs and starts no worries but it does have a few problems.
At low to mid revs it stutters and carries on. It's not happy like this and it doesn't like to rev cleanly.
From mid to high revs it opens up and roars away happily, the exhaust not changes and it's great.
Free revving it doesn't sound very clean either.

I turned the air screw out another half turn from the factory spot (1.5 turns) to make it 2 turns and it ran worse.
I turned it in 0.5 of a turn to make it 1 turn and it ran a tiny bit better, but not really.

Now I have a rough idea of how the jet sizing and needles etc work but I'd like some advice on what to look at next.

Also i've got to seal the expansion chamber on properly, it leaks a bit currently, but not heaps.

The airfilter is clean (and I'm guessing even if it wasn't it wouldn't be the problem since the bike roars away at high revs no worries).

Any help would be much appreciated :).

[Jockney Rebel]

sounds like its running lean.double check for airleaks on the intake side rubbers spray a little wd40 onthe rubbers if it affects the running at all its got a leak .failing that maybe the airscrews or seats are worn..also check the needle height dunno bout ktms but youll usually find theres notches on the needle try raising it one notch..lastly blow out your pilot jet pilot

[Tony OW31]

quote:Originally posted by Jockney Rebel

sounds like its running lean.double check for airleaks on the intake side rubbers spray a little wd40 onthe rubbers if it affects the running at all its got a leak .failing that maybe the airscrews or seats are worn..also check the needle height dunno bout ktms but youll usually find theres notches on the needle try raising it one notch..lastly blow out your pilot jet pilot

Lol, I think the opposite (baring any air leaks) sounds to me like it's running rich in the mid range and the needle needs dropping a notch.

[The Mad One]

Please do not f@ck with a two stroke if ya dont understand them ;) Ya bike is a little old & who know`s what it`s history is. Jetting via a nerdbox is not advisable.
So I am in the area & can help.It will cost you a slab.
Skimpy may still have my #.If not send me yorz.

[JackTar]

Fimp has mates?

[Nebuchernezzer]

I have cheap rates :).

[fimpBIKES]

THE CHEAPEST lol


i have mundy's number, his advice is sound (;)[8][xx(][:o)][:I][8D][:0][:X]) as always
plus i love catchin up with the guy so we shall have to set something up ;)



hey jim, speaking of 2 strokes...

[Nebuchernezzer]

Well I thought I'd check the settings first before resorting to having someone else look at it. I'm allergic to not tinkering myself sorry fellas.

I had a look through the various settings in the KTM manual and found two that would work.

Stock setting:
175 main
42 pilot
1.5 turns airscrew
C needle at 3rd clip

16-25degrees at 0-400m altitude setting:
175 main
45 pilot
1.5 turns airscrew
C needle at 1st clip

Mine was set at:
175 main
45 pilot
1.5 turns airscrew
C needle at 3rd clip.

So i moved the needle to the first clip, made sure everything else was clean and checked the float level. Not run it yet since i did this at 9pm last night in the shed but i'll give her a go this arvo and see how it runs :).

[The Mad One]

Hey Skimpy :D I found another DR800 & will look at it on Sat [8D]in the view to purchasing said bike.
I also know where there is a near complete RG250 WEI ;) fighting off the rats in a shed (the screen is busted)then you can fit a TSS500 & go racing onit [:0]

[fimpBIKES]

i have already aquired the chassis of a RGV and the heart of an XR600 :D

if you want a RG250 let me know, non runner $400 ;)

[Nebuchernezzer]

Hurry up and make the heart of an XR600 go so we can go and fall off in some mud/sand/water :P.