Bikes been sitting for about 2 yrs, no use.

How do you know its a weak spark? Is this a visual check? Will the bike start with the correct new spark plug?
On some bikes, you can hardly notice the spark when looking at the spark plug laying on the head, Try looking at night in the DARK!

Thank you for contacting FixYa with your inquiry.
The KTM factory suggested Oil is 1200cc of 10W-40.
http://dirtbike.off-road.com/dirtbike/review/ultraserious-racing-four-strokes-ktm-520-sx-520-exc-400-sx-and-400-exc-20704.html
If we can be of further service please let us know.
Best regards,
TF

Thanks for contacting FixYa with your inquiry.
Check externally for the obvious things first like a bent shift lever or lever re-installed in a position interfering with frame or something preventing engagement into 1st gear. I'm never that lucky.
More than likely you have either bent a shifting fork or lost a tooth on a gear or something on the shift mechanism internally is bent, broken, or has lost a clip. Drain your oil and check the plug magnet to see if any metal shavings, fragments, or parts appear.
You will most likely have to pull the engine and split the case and replace parts. You can take it to a shop or if your handy do it your self. Take a look at the link to the parts fiche and determine your preference.
http://cyclehuttktm.com/FicheFinderNew/FicheFinder.aspx
2001/400/Engine/Transmission II (Don't know if your bike is a SX or EXC Racing)
2001 > 400 SX RACING > ENGINE > SHIFTING MECHANISM
You can also order a repair manual from this site or ask your dealer

http://www.repairmanual.com/KTM.html

If we can provide other information or service please advise.

Kind regards,

TF

Some people call this a ""cough stop"" assuming the bike is well tuned and nothing else is wrong ,
I use an upper cylnder lube in my wr450f called Moreys and it solves this, it also helps it start easier, I cant explain why, might not work for everyone, but its a cheap solution, hope it helps.

You need to work with a suspension specialist shop to lower your bike. They can take apart the forks and shock and install spacers to limit the travel and make the bike lower. This mod is easily removed in the future if you decide to sell the bike etc.

Try Enduro Engineering or Pro Action There are other local shops that do suspension work... ask around at local shops and the KTM dealer etc.

2001 EXC have the same cooling system regardless of a 4 stroke or a 2 stroke, this technology have stayed until 2006

Here is the manual for 2006:
https://www.ktmdealer.net/uploads/models_tech_datasheets/8303F3_OM_EN.pdf

then your water pump assy should look like this

http://www.ktmcyclehutt.com/ktm-parts/productimages/77335955044_lg.jpg

check the valve clearances.

which one would be the best?First of all there is no sxc it's sx exc mxc. The difference in the sx and exc is the sx is strickly a mottocross bike. It is not geared or setup suspension wise to ride in the woods. It is much more radical than an exc which is designed specifically for woods riding.,,,

which one would be the best?First of all there is no sxc it's sx exc mxc. The difference in the sx and exc is the sx is strickly a mottocross bike. It is not geared or setup suspension wise to ride in the woods. It is much more radical than an exc which is designed specifically for woods riding.,,,