KTM SMC 660 - diagnosis thread

DrSmith · Two Stroke Sniffer Joined: 12 Jun 2009 Karma :

These bikes are notoriously difficult to start, but even after being fairly certain I've acquire the knack, I'm having problems.

I could get the bike running after about an hour of kicking the shit out of it - most times it would start without the choke (though I'd have to use some choke immediately after firing up to keep it ticking over until it was warmed up). Once it's warm I can start it first kick, every time. I decided it must be easier than this and that I can't do an hour of kicking every time I want to go for a ride, and so did some tinkering (foolish, I know). I took the carb off and gave it a good clean. I replaced the spark plug. Still woeful.

A couple of days ago I started messing around with the air/fuel screw and idle screw to see if I could get some sort of change. I reset the air/fuel screw to two turns out. Went through the well-schooled kicking procedure and was getting some gurgling - like it wanted to start but someone was hitting the kill switch immediately after I kick - I consider this progress after hundreds of kicks where I got nothing, but still not starting right.

I randomly decide to try kicking with the hot start button pushed in (bike's still cold) and weirdly the bike starts but then dies after a couple seconds. I then try the hot start button and the choke and it starts and stays fired up. Amazing. But I immediately realise there must be something pretty weird going on if the bike prefers to start with the hot start button and choke on simultaneously from cold.

I let the bike warm up and start investigating the air/fuel screw. I wind it all the way out and the bike is still running. Weird. I wind it all the way in and the bike still runs. Weirder still.

So what does that mean? The hot start button, the mixture screw. It's all a bit concerning. Did I mess something up when I cleaned the carb? Did I have the idle screw too high? Would that cause it to not stall when adjusting the mixture screw? What other tests should I do?

hmmmnz · Super Spammer Joined: 22 Aug 2006 Karma :

ktm's are notorious for running lean out of the box to pass emmissions,
i think its time you took the bike to a dyno and get it tuned properly,
as for the pilot screw, it could be that the passage that the pilot screw screws into is blocked,

i think you need to pull the carb again, soak the carb in kerosene/parrafin and then blow through all the passage ways with compressed it.

my ktm would start 2nd kick with no use of the hot start.
mind you it also had electric start so i hardly ever kicked it over
____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

DrSmith · Two Stroke Sniffer Joined: 12 Jun 2009 Karma :

I've discovered a routine in which I can now get the bike to start rather easily, but I can't understand why this routine works and what the cause could be.

Firstly, I know the bike will not start in the same state as it runs when it's hot. Before I do anything I will unwind the idle screw 2-3 turns, put the choke on, give it a tiny bit of throttle and this is usually sufficient to start the engine. However, since it does not like running in this state, I will have to wind in the idle screw back to where it was so that the tickover is high enough that it doesn't stall. The choke can be turned off immediately after putting the idle screw back to its original position.

What's going on here then? Why won't the bike start with a "normal" idle screw position? What's happening inside the carb that allows the bike to start with the idle screw unwound, and how do I fix it?

Here are my thoughts: Since the mixture screw (air/fuel mix screw, NOT idle screw - carefully making that distinction) had no effect on idle speed when I wound it right in, the manual suggests a smaller idling jet is then required. Would this be because it is making it too rich? If so then this makes sense about me having to unwind the idle screw in order to get it to start - I'm effectively balancing out the mixture by making it leaner with the idle screw so that it will start. Solution: install a smaller idling jet?

P. · Red Rocket Joined: 14 Feb 2008 Karma :

Set carb to factory default, don't touch the mixture screw, you don't have to.

Clean the carb so its spotless.

The idle should be set to 1400-1500 when warm, so get it working and up to temp, make sure its that temp then make sure absolutely everything is stock settings.

Have you had the valve clearances checked too?

DrSmith · Two Stroke Sniffer Joined: 12 Jun 2009 Karma :

P. · Red Rocket Joined: 14 Feb 2008 Karma :

DrSmith · Two Stroke Sniffer Joined: 12 Jun 2009 Karma :

P. · Red Rocket Joined: 14 Feb 2008 Karma :

Enjoy your badly starting bike

DrSmith · Two Stroke Sniffer Joined: 12 Jun 2009 Karma :

monkeyman · Scooby Slapper Joined: 26 Jan 2004 Karma :

There is definitely something not right with KTM

It should start reliably, you shouldn't have to mess with the screws between warm and cold

Try going up a jet on your pilot, also check the choke airway is clean

Alternatively try it on easy start, if it starts easy, indicates a lean condition

The logic being that when cold a lean condition makes an engine hard to start
____________________
Im not the best, but im in the top one
RM 250, Husky TE610, K1 GSXR 750

DrSmith · Two Stroke Sniffer Joined: 12 Jun 2009 Karma :

monkeyman · Scooby Slapper Joined: 26 Jan 2004 Karma :

If you could reply earlier than 236 days with the result that would be great. I need closure!
____________________
Im not the best, but im in the top one
RM 250, Husky TE610, K1 GSXR 750