02 400 will not idle

[jason r]

Can anyone help.

My 2002 GasGas ec400 fse that I have owned since new has started to cut out below approx 2k revs and refuses to idle. Above this its fine, though does start to splutter a little the more this problem is going on.

I have checked basics like wiring and connections and charging rate ok and also replaced the spark plug but no good. The only way to keep the bike running is to hold the revs above 2-3k which is making the bike unrideable and obviously not good for the engine.

Any ideas, the nearest dealer to me with diagnostic computer is over 100 miles away

 

[jimjim]

Does your bike have a idle air control valve on the throttle body?

 

[jason r]

I do believe so, a little brass screw on the side of the throttle body. I have tried making small adjustments but has no affect to the stalling.

 

[Fred1956]

I do believe so, a little brass screw on the side of the throttle body. I have tried making small adjustments but has no affect to the stalling.

Have you checked for air leaks? Lightly spray some WD-40, brake clean, or other substance around the throttle body, intake mounting etc. If the engine stumbles or changes pitch then it is sucking air in that area. First thing I consider when the air screw doesn't have an effect when turned. Just be sure to not spray it in the air filter area or it will 'lie' to you

 

[jason r]

Thanks, will give that a try tomorrow

 

[jason r]

So here is an update on what I have done today

• Charging voltage is good at around 14 volts at idle and revving (though I now know I have a bad battery, more on that in a minute)
• Air temp sensor voltage and resistance readings good
• Coolant temp sensor voltage and resistance readings good
• TPS sensor voltage and resistance readings good

I have wiggled all wires and loom and it will not cut out at that point, so wiring looks good.
I have tried the mixture screw at different setting and turning out 1/2 turn each time, I can hear a note difference during some turns
I have checked for air leaks and there are none.

So despite all this it still eventually cuts out, not as bad as when I was using it, but it still does. I took it for a ride and when it cut out, it turned over slowly and started. Next time it stalled it failed to start, battery no good.

At home I took the battery out and put some jumper leads from a good car battery and started instantly, after a little while it was cutting out again when letting it idle.

Now the thing is every time I am just opening the throttle enough to take it just a bit above idle it is ok (though last time I rode it this got worse).

But for now I am thinking it is just an issue with low revs at idle and perhaps needs increasing by a 300 revs or so. Is this possible or does it need to be plugged into a VDSTS to make this adjustment.

 

[jason r]

Update, please don't ask me how, but where I thought I had fitted the new spark plug, I had in fact not (found it lying in the tool box)

So with that I fitted the *new* spark plug and I think the problem has been solved. I don't use the bike a lot, so have probably got use to a bike running a spark plug that was obviously faulty, and on the very first throttle opening the difference is night and day. Much quicker, much crisper and very responsive and smooth. The idle has now been increased dramatically and after a brief 5 mile ride seems to now be cured

I will try and put some miles on the bike tomorrow to check it has been rectified fully and will report back. Fingers crossed but initial impression is looking good.

 

[jason r]

So, after 2 hours worth of riding today, the bike is running well. Faulty spark plug causing the bike to cut out in the lower rev range now fixed with a new one fitted.