Deceleration surges cured (aka pipe bang)

[xtactical]

I posted a little while back about the annoying deceleration pops/surges that seem to be somewhat common on ktm 2 strokes. There seemed to be a lot of confusion and debate about what they are and why they happen, the most common responses I received were “they are normal” and “your jetting is too lean”. For those that are plagued by these rather annoying and sometimes dangerous surges that occur when cutting throttle on a two stroke i’m happy to report they are NOT normal and they can be cured. 

Seems the most common misconception is they are lean surges or hanging idle, however those are two completely different things than the deceleration pops. I cured these decel pops by fixing my rich jetting. I prefer to run a tin bit on the rich side for cooling purposes but didn’t realize how poorly it was effecting this decel popping. I cured 99% of the problem by simply leaning it out. I noticed that if they would occur at a higher rpm range when engine braking that my main was too rich, once i cured them up high i realized it only happened when i’d chop throttle at low rpm, so I leaned my needle clip and PJ. Just thought i’d share this for anyone having this problem as they can be extremely annoying, happy trails.

[ktm_fastguy]

So you are using the stock Mikuni.  What's the list for your final settings?

[xtactical]

16 minutes ago, ktm_fastguy said:

So you are using the stock Mikuni.  What's the list for your final settings?

It’s bit older so it has the keihin. I settled on this jetting and it’s supreme 35pj NEDH 3rd clip, 160main, 1.5 air screw 

[Wooded]

SO you cured pipe bang on what yr bike?

I never heard of the term before 17/18 and now you cured it on a bike pre 17/18? 

??

[Shhhh]

5 minutes ago, chrismxer said:

SO you cured pipe bang on what yr bike?

I never heard of the term before 17/18 and now you cured it on a bike pre 17/18? 

??

I agree, he doesn't mention the year and model, and I never had pipe bang on any of my pre 17 KTM's.  Mine is almost 100% gone since I put a Keihin on it, 17 250xc... ?

[xtactical]

37 minutes ago, chrismxer said:

SO you cured pipe bang on what yr bike?

I never heard of the term before 17/18 and now you cured it on a bike pre 17/18? 

??

That’s becuase only the pre 17/18 ktm 2 strokes have a special pipe bang microprocessing inductor built in. 2 stroke technology you know... who can keep up?!

Its just crumby jetting fellas, the much mikuni carbs are just accentuating the problem on the newer bikes

Edited March 25, 2018 by xtactical

[Phil Stu]

On 3/25/2018 at 10:18 AM, chrismxer said:

SO you cured pipe bang on what yr bike?

I never heard of the term before 17/18 and now you cured it on a bike pre 17/18? 

??

Because most people simply call it surging on decel (LOL). I've only recently seen the term "pipe bang" and I think it's a silly term used for a fairly common 2 stroke problem.

Edited July 27, 2018 by Phil Stu

[shrubitup]

12 minutes ago, Phil Stu said:

Because most people simply call it surging on decel (LOL). I've only recently seen the term "pipe bang" and I think it's a silly term used for a fairly common 2 stroke problem.

lean surge and pipe bang are two different things.

[Phil Stu]

58 minutes ago, shrubitup said:

lean surge and pipe bang are two different things.

Not to argue semantics but I didn't say "lean" surging. For clarification, During each "pipe bang" the bike does lurch forward, power lunge forward, surge forward, or however you would describe it. You can feel it and it does surge. My 14 has this issue and "Pipe Bang" is still a silly term for it IMHO.

It's explained here better then I can explain it. http://www.powercdi.com/manual/combustion/pipe_bangs/en.html

[shrubitup]

15 minutes ago, Phil Stu said:

Not to argue semantics but I didn't say "lean" surging. For clarification, During each "pipe bang" the bike does lurch forward, power lunge forward, surge forward, or however you would describe it. You can feel it and it does surge. My 14 has this issue and "Pipe Bang" is still a silly term for it IMHO.

It's explained here better then I can explain it. http://www.powercdi.com/manual/combustion/pipe_bangs/en.html

Surging on decel (when throttle slide is fully closed) is more common than pipe bang and is attributed to a lean pilot jet/air screw setting. I've had many two stroke bikes and the only one to have pipe bang is my Beta 300RR which has a motor similar to the 2016 KTM 300. I also have a 05 KTM 300 which doesn't have the pipe bang. Installing RK this weekend on Beta for a variety of reasons. Will update.

[ktmHolland]

1 hour ago, shrubitup said:

Surging on decel (when throttle slide is fully closed) is more common than pipe bang and is attributed to a lean pilot jet/air screw setting. I've had many two stroke bikes and the only one to have pipe bang is my Beta 300RR which has a motor similar to the 2016 KTM 300. I also have a 05 KTM 300 which doesn't have the pipe bang. Installing RK this weekend on Beta for a variety of reasons. Will update.

I will be looking forward to your update. Thinking of getting the rk head next week.

[shrubitup]

On 7/27/2018 at 12:51 PM, ktmHolland said:

I will be looking forward to your update. Thinking of getting the rk head next week.

Quick ride in the neighborhood park: pipe bang not cured, insta-tug right off the bottom torque wise, no idea on better fuel consumption or cooling. Going to ORV area tomorrow for actual test.

UPDATE: unclear if my bang is a surge or bang. JD Jet Kit ordered. My KTM with JD Jet Kit has no issue and runs amazing. I hear the RK likes richer jetting so I threw in a 40 PJ and it's 85F today. That's really rich (seemingly) but it still surges. Will update again next weekend after JD.

Edited July 29, 2018 by shrubitup

[E-TECH]

 Has anyone considered the dangers of pipe bang??

[ktmHolland]

On ‎7‎/‎28‎/‎2018 at 8:18 PM, shrubitup said:

Quick ride in the neighborhood park: pipe bang not cured, insta-tug right off the bottom torque wise, no idea on better fuel consumption or cooling. Going to ORV area tomorrow for actual test.

UPDATE: unclear if my bang is a surge or bang. JD Jet Kit ordered. My KTM with JD Jet Kit has no issue and runs amazing. I hear the RK likes richer jetting so I threw in a 40 PJ and it's 85F today. That's really rich (seemingly) but it still surges. Will update again next weekend after JD.

That's the reason I was looking at the rk head. My 300 surges bad. Getting kind of annoyed. Messed with the air screw and didn't help. Switched out the mikuni for the pwk air striker and blais racing jetted it for me with the jd kit. Bike runs a lot better with the pwk but cant get rid of that annoying surge. This is what they jetted to  Blue needle, clip #2168 main 38 pilot 0-1000 feet is my elevation. one thing I noticed is I don't need the choke to start it when its cold. don't know if this is a good thing or a bad thing. Any help would be great.

[shrubitup]

1 hour ago, ktmHolland said:

one thing I noticed is I don't need the choke to start it when its cold. don't know if this is a good thing or a bad thing. Any help would be great.

Pilot is too rich if no choke to start. Is yours a 17+ model? I hear they have poor sealing reeds which could be your issue.

Here's a thread to read about jetting.

 

[ktmHolland]

36 minutes ago, shrubitup said:

Pilot is too rich if no choke to start. Is yours a 17+ model? I hear they have poor sealing reeds which could be your issue.

Here's a thread to read about jetting.

 

Thanks for the info. I will try a leaner pilot tomorrow. its a 18 300. already changed out the reeds to the v force.

[redrider144]

On 3/24/2018 at 6:42 PM, xtactical said:

I posted a little while back about the annoying deceleration pops/surges that seem to be somewhat common on ktm 2 strokes. There seemed to be a lot of confusion and debate about what they are and why they happen, the most common responses I received were “they are normal” and “your jetting is too lean”. For those that are plagued by these rather annoying and sometimes dangerous surges that occur when cutting throttle on a two stroke i’m happy to report they are NOT normal and they can be cured. 

Seems the most common misconception is they are lean surges or hanging idle, however those are two completely different things than the deceleration pops. I cured these decel pops by fixing my rich jetting. I prefer to run a tin bit on the rich side for cooling purposes but didn’t realize how poorly it was effecting this decel popping. I cured 99% of the problem by simply leaning it out. I noticed that if they would occur at a higher rpm range when engine braking that my main was too rich, once i cured them up high i realized it only happened when i’d chop throttle at low rpm, so I leaned my needle clip and PJ. Just thought i’d share this for anyone having this problem as they can be extremely annoying, happy trails.

I thought you fixed your pipe bang by setting the proper squish clearance on your head?

[Sweet Dick Willie]

Mine got much better with leaner jetting and the RK Tek head. With the stock carb settings and stock head, it was really bad.

[sammyd173]

FWIW I like the the term 'pipe bang' even if it sounds a bit silly, but that's exactly what it is! It's a decent descriptor. 

I just picked up a new '17 250 XC-W and was mortified at how badly it did this and ran off the bottom. Especially considering that my '04 200 EXC positively purrs. JD kit shows up Thursday but I've been thinking that some race gas might be needed as it seems like pre-detonation. 

If this tells anyone anything... I put an old Turbine Core on the bike just to see how it ran on the stand. I started the bike from cold. The pipe bang was gone! and the bike sounded a lot better, even off the choke, for about 20 seconds. Then it came back, albeit muffled from the arrestor. Can anyone tell me what this suggests? Isn't the bike richer at start up, meaning going richer might be better? 

[shrubitup]

On 7/28/2018 at 5:18 PM, shrubitup said:

Quick ride in the neighborhood park: pipe bang not cured, insta-tug right off the bottom torque wise, no idea on better fuel consumption or cooling. Going to ORV area tomorrow for actual test.

UPDATE: unclear if my bang is a surge or bang. JD Jet Kit ordered. My KTM with JD Jet Kit has no issue and runs amazing. I hear the RK likes richer jetting so I threw in a 40 PJ and it's 85F today. That's really rich (seemingly) but it still surges. Will update again next weekend after JD.

OK, RK + JD is a good combo. Bike vibrates less, crazy mid range huge hit [front wheel goes sky high - believe this is due to power valve adjustment made with JD kit (added spring pre-load and removal of small spring)], MPG is same, still surges a tiny bit so going to adjust float next. With added low end power I have more confidence which results in less fatigue. Added low end power also shows how shitty my rear tire is - likes to spin now. Going tubliss and IRC TR-11 soon. RK said to reduce temps - wasn't an issue before (it's a Beta) so can't verify that.