KTM dies on idle

[St3fan]

I have a KTM LC4 600 with a Dellorto carburator which dies on idle. How can I solve this problem?

[rumprump]

There are some very smart people on this forum.I'm sure if you go into a little more detail of your problem, you will get the advice your looking for.

[St3fan]

Sorry, my englisch isn't that good so it's hard to explain.

But the engine shuts down (dies) on idle when I have driven for 30 minuits or so. So when my engine is hot it doesn't idle anymore, but shuts down. The idle screw doesn't have any effect on it. I already screwed it in.

I have a engine from 94 with a 2001 (625cc) cylinder. To make this work the head has been modified to decrease the compression. Because of this I have a strange jetting. I have a 230 main jet, 48 idle jet, K34 needle (If I remember it right). I went on the dyno and I almost got a nice air/fuel line. Accept in the lower revs area. Could A bike die on idle when it's warm because it's lean in the lower revs?

[Burnrider]

Strange you should ask. We had a 2001 400 LC4 that would idle cold and cough/ sputter and die when warm. Cleaned carb, checked jets, replaced fuel, still ran when cold and died after warming up.

Removed spark plug wire, cleaned inside of threaded spike side of cap for the wire, snipped off 6mm or 1/4" of wire. It ran great for the last day and 100 miles. Owner will replace cap and wire this week. His carb was a Mikuni constant velocity.

[dakat324]

Sorry, my englisch isn't that good so it's hard to explain.

But the engine shuts down (dies) on idle when I have driven for 30 minuits or so. So when my engine is hot it doesn't idle anymore, but shuts down. The idle screw doesn't have any effect on it. I already screwed it in.

I have a engine from 94 with a 2001 (625cc) cylinder. To make this work the head has been modified to decrease the compression. Because of this I have a strange jetting. I have a 230 main jet, 48 idle jet, K34 needle (If I remember it right). I went on the dyno and I almost got a nice air/fuel line. Accept in the lower revs area. Could A bike die on idle when it's warm because it's lean in the lower revs?

Usually a bike that dies when warm is one of 3 things.

1. Too Much Fuel

When a bike is cold you need to add more gas by using the choke. And when it is warm the choke will cause a bike to sputter and die. If there is a rich condition with your bike it will cause the symptoms that you described.

Rich could be caused by - improper jetting- dirty air filter- leaking float needle

2. Electrical

Touchy subject- some electrical items can test perfect when cold, but when warm/ hot they fail. The only way to check this is when the bike starts performing poorly. ex- the coil resistance is through the roof when hot, but good cold....

3. Improper Valve Lash

A tight valve might hold enough compression to start the bike but when hot the valve grows and is not seating properly and compression goes way down. If this is your cause DO NOT RIDE THE BIKE! Make sure lash is in spec.

A few questions for you....

First always make sure regular maintenance is done on your bike to prevent 2 out of three of the causes.

Is your filter clean? An overly contaminated filter acts as a choke.

Are your valves adjusted correctly?

Next question pertains to your Dyno runs. What were the Air Fuel ratios at idle to quarter throtle or low revs?

Does the bike run fine if you open the throttle to past half? Does the bike get through the "rough spot"?

Kat

[St3fan]

I just discovered that I set the float height in a wrong position. So I corrected that and I think my bike will be better. I still need to adjust my idle jet + needle because I think it's to richt now

This is the result of my last dyno run http://img178.imageshack.us/img178/5382/dynorun.jpg

after this run I lowered my main jet with 10sizes and increased my idle jet...

btw, how much influence does the float height have? Does it affect the whole revs area?

at post from KAT:

One month ago I checked my valves and they were good. And my float needle(valve) seems allright - edit: a few months ago I already replaced my Needle valve and seat 300 so it's allright

And I don't know if the problem is electrical. When my bike starts it drives very well. If my bike dies I can start it with one kick now.

And my air filter is clean, but it feels very sticky, maybe to much oil on it? Does that also acts like a choke? And should I test my bike without that filter?

And my bike runs fine in all revs area's as far as I know

Edited September 15, 2010 by St3fan

[dakat324]

ST3fan,

Too rich on the dyno run. Do you have a chart relative to RPM or did you just get that one? Its easier for everyone to help when plotted in RPM.

Yes a heavily oiled filter will choke out an engine. I do not suggest running without one even briefly, however it is a pure check of carb setting. Ultimately it is just a bandage and the carb needs adjusting to work with a properly oiled filter.

Most of us like to tune optimally 13.2:1 Air / Fuel.

Your whole run except for the low end was under 11:1. This is on the rich side. Lower the main. This is not the cause of the issues, but definitely hurts efficiency.

What ever RPM he hit the record button was pretty lean. If you have an issue at idle bump up the pilot for sure. I need to see the mixture where your problem exists. He started at a road speed of 40. I need to see idle to 40.

Kat

[St3fan]

The chart that I posted is the only chart I have. They don't have charts which are plotted in RPM.

And I have a 60 idle jet now, but that's way to big I gues espesially now I my float is on the good position. But now it dies very fast on idle, even when it's cold.

Before that my float heigth was to high so the fuel almost flows in automaticaly when it was at idle, so I think that's why it died on idle when it was hot.

[dakat324]

OK, hope I helped a bit

[St3fan]

Mmh

after setting my float height on the right spot like this image my bike almost die immediately.

Here is my jetting

Atomizer beneath Main jet: 272DR

ChokeJet: 50

Idle jet: 48

Tube beneath idle jet: CD1

Needle K29 (clip on second from bottom)

main jet is 220.

What should I change?

I already tried a K51 needle and a K5, but both are to lean. The K29 needle gives me a richer dyno chart... Or has the position of the float height a huge effect on the air/fuel ratio in all revs area?

Also my idle screw doesn't have any effect

edit:

ok, I'm not sure if I set my float level right. How do I adjust my float level in the right position? I have a Dellorto PHM 38 SD carb

Edited September 21, 2010 by St3fan

[rumprump]

You might want to post a question on ADVRIDER to get additional information on your bike.There is alot of threads on KTM's and any extra help is always great. RR