2-stroke low-mid rpm ping

[craig3x]

I have a 2006 KTM 250xc-w, and it runs great once in powerband. However, at lower RPMs, as a i roll on the throttle, it will ping. I happens more often when I am in too tall of a gear for my speed. As I open the throttle more, the pinging goes away.

Here are some details

-Idles fine (using a 40 pilot)

-runs great at mid to wide open throttle (even have some spooging which means I might be richer than need be? using a 160 main)

What can I do about this? I have tried adding octane booster to my gas, but it's not helping. Could it be needle position? Any ideas?

Edited December 29, 2011 by craig3x
mis spell

[ch_250]

Ya, try raising the needle 1 clip position. If ur spooging on top you might want to go down 1size on ur main too.

[craig3x]

Ya, try raising the needle 1 clip position. If ur spooging on top you might want to go down 1size on ur main too.

yeah, I moved the clip 1 spot to make it richer and it solved about 90% of the pinging. Not sure what to do about the few times it does it now. Think richening the air screw 1/4 turn might help? I guess I could move the clip another position, but am afraid that might be too rich. The bike seems to spooge a bit more since I loved the clip, but its hard to tell

[adam728]

Higher octane fuel could help. Not cheap octane booster, as most rate their "points" system as 0.1 octane. So "boosts octane 5 points" actually means it takes 91 octane to 91.5.

You could try adding toluene for a tank and see if that helps. Can be mixed up to 25% with gas and will raise octane. Toluene is approximately 114 octane ([R+M]/2), so mixing it with 91 pump (I don't know what's avail in your area as premium, so I'm using 91 as an example) will yeild

10% - (114 + 9*91)/10 = 93.3 octane

20% - (114 + 4*91)/5 = 95.6 octane

I've used it in the past without issue. It's the main ingredient in many octane boosters, although you can see you need a fair quantity of it to get substansial boost. Also note that these are just estimates on the new octane rating. It varies depending how the fuel and toluene compounds actually react with one another. Just like mixing 50/50 with 90 pump and 100 race fuel doesn't necessarially mean you get 95 octane in the end.

Pretty easy way to test if you simply need to run a little better fuel to get rid of your ping. If it is the cure then I'd suggest going to a race fuel for a long-term solution. Toluene isn't really any cheaper once you add everything up. But picking up a quart for a one time test is cheaper than buying 5 gallons of race fuel and finding you don't really need it.

[craig3x]

Higher octane fuel could help. Not cheap octane booster, as most rate their "points" system as 0.1 octane. So "boosts octane 5 points" actually means it takes 91 octane to 91.5. QUOTE]

good point. I've heard that octane boosters are misleading. I would like to try some race gas and see if that fixes it. Unfortunately, it's not available everywhere.

[ch_250]

High octane fuel is for high coMpression problems only. If Race gas fixes your problem u know ur compression has been raised. If compression is not your problem, you can order another needle and get the effect of moving your clip half a position. I would still go down 1 size on te main though to stop your spooging at high rpms.

[craig3x]

High octane fuel is for high coMpression problems only. If Race gas fixes your problem u know ur compression has been raised. If compression is not your problem, you can order another needle and get the effect of moving your clip half a position. I would still go down 1 size on te main though to stop your spooging at high rpms.

good point ch_250. There is a chance that the compression might be higher than stock. I think I may try a size down on the main as well, however the JD jet kit recommends the 160 main. Of course I know that isn't going to perfect for everyone's bike. I do have one more clip position I could move to on my needle. I think I'll try race gas first, then needle position....just to see

[ch_250]

Goodidea, then u no. One other thing to consider, i dont no about your ktm, but my yz has an electronic power jet that comes on at 3/8 throttle and turns off at 5/8 throttle. Mine waS running rich a bit below middle and i had to go down 1 size on the power jet. Very rare problem, but a slight possibility.

[craig3x]

Goodidea, then u no. One other thing to consider, i dont no about your ktm, but my yz has an electronic power jet that comes on at 3/8 throttle and turns off at 5/8 throttle. Mine waS running rich a bit below middle and i had to go down 1 size on the power jet. Very rare problem, but a slight possibility.

nope, nothing fancy like that on my bike. no electronics on the carb. I'll stick with trying the race gas, then moving the needle another notch if needed

[adam728]

Other factors besides compression ratio come into play for detonation. A bike with too much squish clearance is more prone to deto than a bike with exactly the same compression ratio but a better squish clearance. A bike might not detonate with me on it running pump gas, but hand it off to a AA or Pro rider that can really hammer it and put more heat in the engine and it might detonate.

[craig3x]

Other factors besides compression ratio come into play for detonation. A bike with too much squish clearance is more prone to deto than a bike with exactly the same compression ratio but a better squish clearance. A bike might not detonate with me on it running pump gas, but hand it off to a AA or Pro rider that can really hammer it and put more heat in the engine and it might detonate.

so, if it's a squish is the possible problem, am I ever going to be able to get rid of the pinging by adjusting carb needle/jets?

[adam728]

so, if it's a squish is the possible problem, am I ever going to be able to get rid of the pinging by adjusting carb needle/jets?

Jetting a touch rich can band aid it. Or running higher octane.

This is a common problem on a fair number of stock bikes. Ideally a 250 will run something like 0.40 to 0.50 mm of squish clearance (lots of different ideas on whats "best"). Lots come with something closer to 0.70 mm because of tolerance stack ups. If an engine makes piston-to-head contact at 0.38 mm of cold clearance, then the factory can't aim for 0.40 mm if manufacturing tolerances are +/- 0.20 mm.

Here's some info and pricing on how to check your squish and cost of mods.

http://www.rb-designs.com/squish-band-test.htm

http://www.rb-designs.com/head.html

And all of this could be meaningly. Maybe you are just a little lean of ideal and need to step the needle up half a notch.

[Fistfullofthrotl718]

This is more of a question then a statement on the topic, but won't retarding the timing a little help with pinging?? I know not a machines have an adjustable stator but on the ones that do, couldn't that help?

[highmarker]

+1 if it is in fact ping he is hearing, not just some other twostroke cllater from the exhaust valve rattleing, pipe, springs, chain slap etc.

Much better to take some timing out than drown it with fuel, doubt the squish bit you never know?

This is more of a question then a statement on the topic, but won't retarding the timing a little help with pinging?? I know not a machines have an adjustable stator but on the ones that do, couldn't that help?

[Bschu]

40 pilot seems too fat to me. I have a 07 xc, I run a 38 pilot...What Needle are U using? IF jd....I would try the KTM needles provided with the bike...I am running the "h" needle...this is the leaner action of the 2 KTM provides. I ran the "g" needle for awhile and have changed back and forth and have stayed with the "h" needle. When I bought my bike from previous owner it had the jd kit in it....I thought the JD needles were a little lazy compared to the KTM ones. I jetted accordingly using the factory book...then leaned up the main to a 160...This is just my thoughts......

[MrBlahh]

if 1 clip change fixed most of it, go 2 clip changes

at partial to mid throttle your on the needle, you can try different needles, it's cheap and easy to swap them out, my bike had nasty ping at 1/2 throttle under load (sand riding) I had to switch needles completely to clean it up

I switched to a N3EJ from yamaha YZ250 at #3 and that cleaned mine up

[BlackCR25098]

You never stated what Octane your service manual recommends AND what octane you're in fact running? Some really crappy fuel we use nowadays that wasn't being used back in the day. You have an 06, so maybe they compensated for it in the manual.

Try finding an ethanol free gas station around you. It's not necessarily a higher octane, but it's a MUCH better fuel obviously. I found one a mile away from me and have been using it ever since my rebuild. My manual recommends 92 and so I use 92. I've heard that being too high is okay, it's too low that causes the pinging. There is a website where you can enter your area and find the closest ethanol free station.

What ratio are you mixing at? You should be at 32:1 and NEVER change. Changing your jetting for pinging is just a bandaid for the real problem. This is like when people have a jetting problem and try to change their premix ratio (which should NEVER) be changed. They are just band aids for the REAL problem. The real problem here being your octane. I'm betting that you're just running too low of a octane, regular when you should be at premium. Let us know what you're at.

[MrBlahh]

Changing your jetting for pinging is just a bandaid for the real problem.

not true at all, pinging on two strokes can and usually is from being too lean

[BlackCR25098]

Does anyone have a video of a 2 stroke pinging? I can't find one. My bike is doing something that I want to make sure isn't a lean symptom. It's jetted according to manual at 32:1 but on cold starts the bike starts and idles amazing (which I want) and when I rev it up the revs don't hang up but it goes whaaaa bing, bing, bing...as the RPM's are coming down slightly after I let off. I'm not talking about the popping from the silencer either it just kind of stutters after the rev up as it's coming down. Is that normal? I believe my jetting is pretty darn accurate.

[BlackCR25098]

not true at all, pinging on two strokes can and usually is from being too lean

So what are the symptoms of running too low of an octane in a 2 stroke then?