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Detonation on decel . Ktm exc 300 2013

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So bike is exc 300 2013.

Head mod, squish around 1.38mm

SXS front piece. 

Jetting: 40p N8RH#3 172 main j. As 1

Elevation 500-1200m

Temp 15C

My problem is pinging on deceleration. 

Was very bad with N8RW#4. On test, at WOT the engine start to detonat, I think, so bad than I can't kill the engine with kill switch!!!!

With N8RH#3 I have VERY small amount of detonation. BUT is a bit too rich on bottom. I can't use leaner needle become detonation will start to hear. Idle is not so good, is like lean on pilot...

What to do to clean up the bottom but to stay safe? 

 

I was playing with NECJ#4 168 main jet. Very clean on bottom and very good idle.

But is a bit too lean for my taste. With suzi  needle is richer in clip #3 ? 

 

 

can crank seal to have some effect to my problem? I have 185 hours on engine.

Edited by adriano.ro

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Why not go bigger on pilot with air screw further out ?

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I was thinking about that but, isn't very common 42 pilot on ktm 300. On 250 May be. 

Next step is richer pilot.

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3 hours ago, adriano.ro said:

So bike is exc 300 2013.

Head mod, squish around 1.38mm

SXS front piece. 

I was playing with NECJ#4 168 main jet. Very clean on bottom and very good idle.

But is a bit too lean for my taste. With suzi  needle is richer in clip #3 ?

What's this SXS "front piece"?

What octane fuel are you running?

As with any needle, from the top of the needle, the clip positions run from leaner to richer as you move down the needle positions. So 3rd from top is leaner than 4th from top. You're dropping the needle going from 4 to 3. When you drop the needle, with the needle being tapered, a larger diameter of the taper fills the mains orifice, so less fuel can pass= leaner.

Are you saying the "very clean" bottom end with the NECJ is too lean for your taste? Or is it it's midrange? Try the NEDJ on #4.

What method are you using to tune the AS?

An NECW( W=i in the alphabetical nomenclature, stupid I know) will be 1/2 clip richer than the J on the starting diameter, for that bottom end and idle if you think the J on #4 is too lean but don't want to go to the full clip of #5. Or go to a NECH for a full clip change over the J. Keeping it on the 4th where you're current at would be like putting the J on the 5th.

If the W or H works better for you on low end and idle but still think mid is lean, try the richer mid NED* needles.

Edited by Trailryder42

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SXS pipe I want to say.

I know how the needle work, about clip position etc.  I drop from 4 to 3 but I put in a richer needle. On keihin  carbs the needles are made to work the best in 3 clip position so that is the reason why I try to find a needle that works ok in that position but to not have the detonation.

 

About AS, I keep a bit open the throttle then I adjust the as until the idle is maximum faster.

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6 hours ago, adriano.ro said:

On keihin  carbs the needles are made to work the best in clip position 3 so that is the reason why I try to find a needle that works ok in that position but to not have the detonation.

About AS, I keep a bit open the throttle then I adjust the as until the idle is maximum faster.

Your statement that needles are made to work the best in clip position 3 is misleading. Sure, the needle may be made so that the middle of its tapered section is at the 3rd clip position when inserted to a certain point within the mains orifice. But whether the 3rd position is optimal for fuel delivery depends a lot on the main jet size.  

If you run 3rd position and midrange is too rich and you wanted to keep that 3rd position, you'd decrease the main jets size. But that's not practical because a main jet change by just 1 size would lean things way more than just a 1 clip position change of the needle to #2. That's why we have those small increments of change to the midrange with the needle. You can't make small enough jetting changes with the main.

As for adjusting the AS, adjusting for highest rpm like you're doing is not optimal for performance. Highest rpm often equates to leanest air/fuel ratio.

Try the "whack the throttle" method. Quickly blip the throttle open off idle to at least half. Adjust the AS so you get zero hesitation, no stumble off idle when you blip it. You can use big 1/2 turn increments to get you close, then back off to 1/8 turn increments to fine tune, giving the engine several seconds to settle in with each new setting before testing, then making another adjustment. I think you'll have better idle, throttle response off idle and less detonation.

And you set don't idle "speed" with the AS anyway. You set your desired idle speed with the idle speed knob. So before doing the "whack the throttle" procedure, set the idle speed you want with the idle speed knob on a warmed up engine. Then as you do the procedure, adjusting the AS for best off idle response, if the idle speed changes significantly, keep it where you want it with the idle speed knob and continue to adjust the AS until you get a clean off idle response.

Pay attention to how many turns out that point is on the AS. Ideally, you want that point to be more than 1 and less than 3 turns out. If its outside those points, you're looking at a pilot jet change.

Edited by Trailryder42

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Hmm. About AS, in this moment I can't open more the 1 turn out AS because the detonation is more pronounced. 

From what I know,detonation is lean effect from pilot,needle side. 

So more I turn out the screw,more detonation. 

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You said you were playing with the NECJ. Is that what you're running now or did you go back to the N8R* needles?

Let's be clear of what you're calling detonation. Describe what detonation is to you.

Detonation happens inside the cylinder and under certain conditions can happen inside the pipe. In the cylinder, it happens after normal combustion from the plug firing. Any remaining unburned fuel then lights off due to heat and pressure because fuel octane isn't high enough to prevent it. We perceive that pressure spike as a knock or a ping.

You have decreased your squish by about .5mm from stock. That's why I asked what octane fuel you run. When you decrease squish, you increase compression ratio. Higher compression ratios require higher octane fuel. You might try removing the fuel currently in your tank, buying a gallon of the next higher octane fuel and try that, at least to rule out that it may be octane related.

Getting a popping out of the exhaust on deceleration (pop pa pop pop pop) is not detonation. But it is caused by too lean of a pilot system/AS setting. If this is what you're experiencing, I agree, you should try a 42 pilot. That will make you have to turn the AS out more to find the same condition you get now at 1 turn out with a 40, and move that point closer to a more ideal, halfway setting between 1-3 turns out. Having the screw backed out more also gives you a wider range of adjustment for making fine tuning, without the huge effects that only minute adjustments can have when the AS is set to within 1 turn of being closed off.

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I'm sure about detonation on my bike. Because I was playing with jetting and have removed the effect for the most part.

I'm use 95 octane gas. Is the lower in my country. To try 98?

Now I have 40 n8rh#3 and 172,may be I can use 170 but I don't have atm. only 168 witch is a bit to lean.

With 40p n8rw#4 172 was waaaaaay to lean on needle!! On WOT, when I was testing the jetting I could not stop the engine with the kill switch!!!!!! WHY DID THIS HAPPEN?

N8rh#3 vs necj#3- the power is more pronounced with n8 on whole rage  but is not so smooth on bottom like necj,and that because my AS is to much in.

 

 

Tnx a lot for replay.

Edited by adriano.ro

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The NECJ is a triple taper needle, so yes, it will be smoother. If the N8 is only a single or double taper needle, it's throttle effects will be more abrupt/pronounced.

What octane measurement method does your country use? RON, MON or (R+M)/2 ? It should be stated on a sticker on the pump. I'm guessing you're in Romania. With you stating that 95 is your lowest grade, I'm guessing your part of the world uses the RON method. The same gas that is rated 95 there would be rated around 88 here in the US.

If that is so, your lowest grade is too low for your engine, especially with the decreased squish. I would definitely recommend trying the higher/highest octane pump gas you have available without going to special race gas.

I would do this right away, to at least rule out your problem isn't octane related and to keep you chasing your tail over this trying to fix it with jetting, if it is indeed the problem.

 

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We have only RON gas. 

What I find interesting is the difference between the gas from 2 gas stations in my town. 

Is about only 95 RON, if I put in from one gas station the bike run normal( this experiment was before detonation scenario) but if I put gas from second gas station, only 95ron gas, with the same jetting and the same temp. conditions the jetting seams rich.

So this is a good or bad thing, about the gas?

Can a good fuel to have this richer effect on jetting?

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If your fuel distributors there are like ours, they mix fuel according to what the gas station wants or to the specs of a particular brand of gas like Shell, etc.. Different ratios and kinds of additives, detergents and such. You may be getting a fuel that doesn't play nice with a dirt bike 2 stroke engine, because those specific additives and detergents and amounts of them in the fuel are causing the fuel not to burn/combust properly/completely in your engine. That would make it seem to run rich. There's also the possibility that the stations tanks are contaminated and your getting bad fuel.

I would start buying only from the station that you seem to have gotten good gas from and the bike ran properly on. But try their higher octane. Buying from stations that see a lot of business is usually best, because of the frequency they have new fuel delivered.

95 RON, in my opinion, is not high enough for your engine.

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Interesting fact is my car, witch have 1.8l engine and 200hp and is very sensitive to gas quality. He runs better with gas that made my bike to feel  richer.

 

Oh, my gas stansions in my area use max 5% ethanol.

 

In the end I have 2 options:

1 using fuel with higher octane ( May be with 99 octane will be ok even NECJ)

2 using bigger pilot jet.

 

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Update: I like topics with solutions in the end. So in my case:

To stop detonation on decel I have changed gas octane to 99ron.

I have also changed the needle, pilot and main jet.

Now I have 42p NECW#3 168 AS1.5 temp around 5C. 

 

Anyway the solution was higher gas octane.

Bike rips!!

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Update 2th part:

!!!!!!!!!!!!!!! If u go richer on pilot and needle and u still have detonation I found THE PROBLEM!!!!!!!!!!!!!!!!!!!

 

in my case ,the SXS doma pipe seems to need more fuel than standard pipe,and after u release the throttle some kind off turbulence is made in carb,and the slide can't go to the bottom fast enough!!! 

 

SO I PUT PUT MORE PRELOAD ON SPRING AND NOW I DONT HAVE ANY DETONATION EVEN IF I GO MUCH LEANER!!.

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