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Discussion Starter #1
I have just fitted a new piston added to my 250 EXC-F ( 160 +hours), so am hoping to finally get the bike to reliably tickover ... There was some oil in the airbox, but not a lot. The old piston showed some signs of wear, happy to see that it was not a lot.

Everything is now back together, still not got a reliable tickover. I fitted JD Jetting kit a while ago which did improve things somewhat, but not to the extent you could say it was reliable. I fitted all parts exactly per the instructions. The bike is big standard , apart from the JD kit.

So, to the reason for my post...
To anyone that has fitted a JD jet kit to a 250 EXC-F ( 2007 model to be really exact !): What settings did you end up with for the idle mixture adjustment screw?

The instructions went a bit wierd about that point. There was no mention of the EXC-F or ECX-W models. The closest is the SX-F, where it says to start off with the screw 2 1/4 turns out. The owners manual for the SX-F has the factory setting at about 1 1/2 truns out (IIRC), but the factory settings for the EXC-F is only 3/4 turns out.

Did you ignore the JD instructions and leave at 3/4 out? or, did you richen the mixture by an additional 3/4 turn, same as that applied to the SX-F? Or, did you find a wholly different setting was needed?

I want to get to a good basic setting, hopefully with reliable tickover, then adjust the TPS settings, if needed, to get it as near perfect as I can.

This bike has been cracking fun, but I am looking to move up to a 450 now, so want to sort out those niggling things that you nomeally just learn to live with before selling it on.
 

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Set the screw to 1½ turns out, start the bike and get the engine up to operating temperature.

Adjust the idle as low as possible without stalling.

Slowly turn the screw in until the engine starts to slow down and then unscrew 1/2 of a turn. The screw should be in the 1 to 2 turn range. If it is less than 1 turn, the pilot is too big - install the next smaller size. If it is more than 2 1/2 turns the pilot jet is too small - install the next larger size.
 

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ktm manuals tuning section should read like that;
spot on Kev
 

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Hi there,

Jumping in a little late but I have an 07 EXC-F with the JD kit. I'm running 2 turns out with a #40 pilot, it is the high end of the fuel screw but a #42 pilot is too rich.

I have to adjust the idle speed up slightly until the engine is hot; then tweak it down.

What pipe are you using?

Have you ever replaced the carb slide if you have an erratic idle?

What is it like on choke when cold?

Cheers, Nick
 

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I hope the slide plate is the correct way round... hole at the bottom.

Someone gave me a carb to look at the other day, slide plate was upside down in it!
 

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Discussion Starter #9
Hi Nick,

The pipe is bog standard;

I have not replaced the carb slide, so I believe it is still the right way round ;-)

It starts fine on choke, but once it gets hot has become unreliable at idle.

It was fine after I fitted the JD kit, then became increasingly reluctant to idle when hot.

I have just replaced the piston because I am looking to sell this to move up to something in the 450 size, didn't want the tyre kickers to sniff at high hours on the piston.

Whilst I am at it I want to try and get this idling nonsense licked, it seems to bethe Achilles heel of this motor.

I moved the idle mixture screw when I took the carb off, and do not know where it was at :redface:
 

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It does sound like a teaser, the carb on the 250F is a little too big really but that is just my opinion before I get screamed at!

Did you totally remove the carb? Where was it placed if off the bike; Im wondering if the air jet or start jet is partially blocked, they live inside the trumpet of the carb rather than in the float bowl!
Does the slide fully close when the throttle is closed? Im assuming its ok when revved and not the standard plug cap breaking down! Do you have to apply a little throttle to start the bike or just press the button/kick it?

Just trying to get to grips with your bike's quirks before I give dodgy advice.

Cheers Nick
 

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Discussion Starter #11
Thanks everyone for your replies so far. The main problem I have is that the idle mixture adjustment screw does not seem to do anything unless it is crewed almost fully in, in which case the engine just stops.
I had been running the JD red needle, #180 main and #40 idle. The carb has an after market idle mixture screw that makes adjustments easier. Since the rebuild I cannot get a reliable tickover, engine idles for about 30 seconds then dies, won't restart without a squirt or two on the throttle, then needs throttle closed. It runs fast as soon as it fires then settles down - for about 30 seconds.
Something not right somewhere, I decided to strip the carb down for cleaning, once I took the mixture screw out I think I spotted the problem, or at least another candidate ..No spring, washer or O-ring. When fitting one of these after market screws, are they not meant to retain these items from the original screw?
It has run much better than it does now; I am hoping that this might be the answer.
 

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Yes, the missing O ring is your problem. Needs the spring as well to stop it winding out.

If its aluminium, make sure you dont overtighten it or the tip breaks off in the carb and its junk :eek:
 

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Hi again,

Not sure which aftermarket fuel screw you have but they should come with spring, washer and o'ring. Kev is right, as you would expect; no insult intended, the fuel screw must seal at the carb with the o'ring to ensure correct fueling. If you have been adjusting it a lot, check the tip to ensure there are no witness marks on the shoulder through over-tightening; the last thing you need is the tip to fall off and become embedded in the fuel flow line.

With the needle and jets you have supplied I would expect somewhere between 1-3/4 to 2 turns out on the fuel screw.

Good luck.

Nick
 

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Discussion Starter #14
Hi Nick,
It looks like the Prolite/Pulse screw, it was already fitted when I got the bike. I checked with my local bling emporium, and these do not come with any of the required spring, washer or o-ring. It's odd that it seemed to work reasonably well for a while, I couldn't cure a bit of bogging by adjusting the mixture, so had the carb stripped and checked by my local KTM centre. They also replaced the spark plug cap and plug, and checked valve clearances. After that I fitted thw JD kit and it has been a gradual decline from there. When I fitted the jets I assumed all was well and no spring, o-ring etc, was used on this model of carb - Doh! There was none there then.
It was only whilst researching here I came across a few references to not forgetting these parts when fitting a replacement mixture screw...Thanks for the tip about the tip, all looks fine. I will definitely take care with the rebuild; I am hoping this is the last stage in curing this niggling problem.
 

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It's a common problem this bogging, lean or rich!

I have been given some set-up info but haven't got round to trying it yet.

It's for the accelerator pump timing. You have to insert a length of 1mm wire under the slide and then adjust the timing screw for the pump to touch the cam if that makes sense to you. It was also reccomended to fit a SX spring on the Acc pump instead of the O'ring mod; that should remove the bog completely. The O'ring just uses more fuel; even with a leak jet. No #60 leak as well by the way.

I hope this helps; I will try it when I rebuild my bike but thought I'd share it with you as your struggling.

Cheers

Nick
 

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Discussion Starter #16
Wouldn't say it's a struggle, more a tortuous voyage of discovery ... KTM and JD info is not the most concise.
Where does that 1mm wire go? Under the throttle slide? But the slide does not bottom out, unless the idle speed screw is wound all the way out, or is that required too? It does sort of make sense; providing an initial setting for the acc. pump...
 

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Hi again,

Idle adjust has to be fully out, it shouldn't be "in" a great deal, the idle fuel circuit is up and over the slide. The 1mm wire holds the slide up, just insert it at the edge. It give the timing for the squirt commence, the leak jet adjust the duration.

Cheers Nick
 

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I fitted a 50 leak jet, SXS spring and lockwired the acc pump mechanism together. Throttle response was spot on, all I have is a slight lean feeling mid/top but thats cos I had an SX can fitted and did not change needle or main....
 

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Discussion Starter #19
Kev, Nick,
Thanks for your all your advice. It is now back together and running better than it ever has. I cannot for definite the exact reason for it idling so badly though; I have now stripped,cleaned and rebuilt the carb with a new seal kit; to try and sort this once and for all.

Things that were wrong were:
No O-ring on the idle mixture screw.
No clips on the breather pipe, this was quite loose at both ends.
The idle jet was blocked.
The idle air jet was bunged with oil.
The accelerator pump adjustment was way off.
The accelerator pump diaphragm was corroded.

With new seals throughout and rebuilt it with JD red needle ( 5th groove), #42 idle, #185 main and #60 leak, idle screw is 2 turns out.

The bike runs like new now, better than when I bought it. It started on first ouch of the starter, idles lovely and pulls like a train.

It seems a shame to be selling it now, but I paid the deposit last week on a new Sherco 4.5Fi. Need some cash soon to pay for it.
 

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Hi Kevin I was told your the man for ktm's by a friend you've done some work on their carb.

Iv got a xcf 280 2008 running an akroprovic system but it's running really bad with flat spots and cutting out from sharp revs.

Is there any thing you can do with this? Do you know best jet sizes for this?
 
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