Hi I had an 03 that I had converted (Marsh Performance). I ran 14/50 before and after and the main improvement was it was less likely to stall if you let the revs drop and you were able to use second on climbs and it had more low down grunt.. When Swampy did mine he replaced the inlet valves which is common so probably worth checking these while you are in there. I traded mine in for an 07 450 which is a different bike altogether,'feels' heavier but the wider gear ratios are nice ( the 350 kit hilights the closeness of the250 gearbox) I  think for the money its worth doing if you are happy with the bike now. But if you really want a 400 or 450 the kit won't make yours into one. Cheers'. Landy

It was probably me you were thinking of - I did mine about 9 months ago. Actualy its the second one I've had , wore out the first and liked it so much I got another just the same.
Between the two of them I've done a few H and H, LDT's and thousands of miles of trail riding, and I've only very rarely wished I had more power. Its plenty quick enough for me - I honestly dont think any of us have the talent to exploit a 450 to its limits. Personally I like to be able to thrash my bike from time to time - its the oik in me, I guess!! Getting the throttle on the stop and the revs on the limiter once in a while on a racetrack is one of lifes big bonuses!!!!

A couple of things tho. The first one I had was an 04 with an HT Racing 351 kit fitted to it, from new, by its original owner. HT Racing are a yank tuning company - look em up on the internet - who do alot of KTM performance parts. Current one is an 05 bike - very similar, some minor changes, with an SXS KTM big bore kit which I fitted myself. Very simple to do - just swap piston and barrel and change the carby bits that you will need to buy with the kit. Theres nothing I can really put my finger on , and as I never rode the 2 bikes back to back, but I think the HT Racing one was a better engine. It seemed to have a fatter midrange than the SXS version. Theres nothing actually wrong with the current bike, but I have this nagging doubt that its not as good as the first one. I have read stuff on the US KTM forums that seem to back this up. If I was going to do it again, I would go for the HT kit I think. Its a little more complicated as you need to send your barrel to the states to get it bored. The HT piston is forged , the SXS one is cast, so HT is stronger for the weight.

Also, jetting is crucial. Get someone who knows their stuff to sort the jetting - Justin Gibbs has done mine - you wont get the full benefit if its not sorted properly.

As regards gearing, I've settled on 13/48. Not good for much more than 60mph on the roads without revving the nads off it for long periods. But first is suitably low for the really tricky stuff, and the extra cc's mean it will pull 2nd and 3rd on most trails quite comfortably. For those really slippery up hill moments it will easily pulll away from a standstill in 2nd.

Thanks for info my mate has just turned up on one he bought on ebay
i had a ride and its much more grunty his gearing was 13/47 so 13/48 seems ideal
see you out on trails soon
Cheers
Martin

Despite the fact that the manual says they all weigh the same and have identical chassis and suspension, the 250 feels lighter to ride. I've read thats it to do with rotating mass within the engine, although which bit in particular is lighter on the 250 I dont really know - possibly a lighter crank? Whatever the reason, the 250/350 feels nimbler, lighter , more exciting to ride. The close ratio gearbox also helps - they are very quick up through the gears.

Simon Twig rode mine yesterday for the first time and said it felt light. I rode his - 09 400 exc - and it felt very smooth and civilised by comparison. We then had a little drag race across a stubble field. Mine was possibly quicker off the mark, but Simons out dragged it once we got moving.

Cost wise I think its probably worth it. Many people will disagree with me, but having ridden a 350, I find the 250's just that little bit gutless. They go well, but you have to rev them to get power. I like the extra grunt the 350 gives. Clean and tidy 400 exc's are quite hard to find, and the newer ones are too expensive for a peasant like me. But I found a mint condition 05 250, never used off road with less than a thousand miles on the clock, and converted it to a 350 for about £2800.

The RFS engines seem to be pretty indestructible, as long as they get lots of oil changes. My last one had 400+ hours on it when I finally got shot of it, needed inlet valves during that time but nothing else.

One other thing to mention, for anyone who's got one or is thinking of it. Apparently alot of those engines left KTM with the wrong type of thread lock on the primary drive nut. Mine came undone twice while I had it. The noise is apalling - sounds like its going to explode. If you are unlucky, its possible to put tiny cracks in the slot that the woodruff key sits in on the end of the crank. The slot enlarges ever so slightly, and the key doesnt sit properly, so the nut works loose over time again. The first thing I did on the new bike was to get some permanant thread lock on it and do it up as tight as it will go with an air ratchet. 4000 miles now and it hasnt come undone yet!!!