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General SportbikesThis area is made for sportbikes in general. Posts that dont really belong anywhere else besides here. Questions can be answered and addressed to fully understand certain aspects. If your question is Manufacturer specific please post it there.
I've got pod filters, a jet kit, and a straight through 2-1 race exhaust on my Ninja 250. When I'm travelling at high RPMs and then let off the throttle, I get some crackling and sometimes a rather loud popping sound.
It is ONLY when I'm coming down from high (over about 8k) RPMs and it's ONLY when the throttle is completely closed.
Is this something that should be normal considering the modifications I've done to the engine??
I found this online, and it seems to say that this is a normal situation:
Quote:
Originally Posted by Some Internet Page I Found on Google
Engine backfires: It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm. The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers for this to occur. (No mufflers/headers etc.) Why This (normally) Happens: 1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system. 2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat. 3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there. 4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires Other possible causes: Air Leaks: Any source of fresh air into the exhaust system can create or worsen the conditions that bring about exhaust popping. The most common entry point is the junction of the header pipes and mufflers. Even a small air leak can dramatically increase the intensity or likelihood of exhaust system popping. A high temperature silicone sealant, as can be found in many auto parts stores, may be used to seal the pipe/muffler junction. Lean Carburetion: While exhaust system popping may be considered normal, it is certainly made worse by an overly lean idle circuit. Be sure that your carburetor's pilot jet is the correct size and that the idle air mixture screw is correctly adjusted before looking for other causes of popping. The procedure for adjusting the pilot circuit is covered in the Tuning Manual. Ignition: If exhaust system popping is very loud, irregular and accompanied by loss of power, then you should suspect that the ignition system is not performing as it should. If, for some reason, the ignition sometimes fires at the wrong time, then exhaust popping can become very energetic (loud). Look for failing high tension leads (plug wires), failing ignition coil(s) and especially switches or connectors as possible causes.
But I would like to get some other's input on it before I just stop worrying about it.
For what it's worth, when I pull the spark plugs they showed a light grayish color. No damage or anything. I can't remember how long they've been in there. I took them out to put the new ones that I just got in. Gray, from what I'm finding, is a relatively okay color...but it does signify running a little lean...
Should I rip the jets out and start messing with them?? The bike pulls hard from idle to top end and doesn't have any stutters or sputters or anything...I THINK that the jetting is done correctly, I messed with it alot last fall...but the popping is kinda messing with my head.
***EDIT***
I just found out that the spark plugs that I have are for cold weather. I should be using some hotter heat range plugs. I just ordered them. Would this have any kind of effect on why that plug is showing that it looks a bit lean??
__________________ --In Life, Try To Be The Kind Of Person Your Dog Thinks You Are...
--Colts, 49ers, Lions, Detroit Red Wings, Detroit Tigers, USC Trojans, MSU Spartans, LSU Tigers
--2002 Kawasaki Ninja 250--SV-650 rear shock, Sonic Springs .80kg/mm front springs, ZX-2R graphics, flush mount front signals, tail pod rear signals, Kerker 2-1 race pipe, Factory Pro Stage 3 jet kit, UNI pod filters, ZG Double Bubble, Custom Creations soft vinyl seat cover, Kawi Green rim stripes, carbon brake fluid cap, carbon control levers, No Rear Fender, Yamaha R1 Style Mirrors, V-LEDs.com H4 HID Kit, Nelson Rigg Silver Streak Mini Saddle Bags, Rapid Transit Recon Tank Bag, Various Manufacturers Decals
Last edited by Gimpdiggity : 04-07-2008 at 06:15 PM.
It's quite a bit quicker, actually...and the suspension mods have made it handle even better than it did before.
__________________ --In Life, Try To Be The Kind Of Person Your Dog Thinks You Are...
--Colts, 49ers, Lions, Detroit Red Wings, Detroit Tigers, USC Trojans, MSU Spartans, LSU Tigers
--2002 Kawasaki Ninja 250--SV-650 rear shock, Sonic Springs .80kg/mm front springs, ZX-2R graphics, flush mount front signals, tail pod rear signals, Kerker 2-1 race pipe, Factory Pro Stage 3 jet kit, UNI pod filters, ZG Double Bubble, Custom Creations soft vinyl seat cover, Kawi Green rim stripes, carbon brake fluid cap, carbon control levers, No Rear Fender, Yamaha R1 Style Mirrors, V-LEDs.com H4 HID Kit, Nelson Rigg Silver Streak Mini Saddle Bags, Rapid Transit Recon Tank Bag, Various Manufacturers Decals
If your bike has an air induction system, thats the sound it makes when its working
After a high throttle application, when transitioning to off throttle, there is a lot of unburnt fuel that gets blown into the exhaust system. The air induction system pumps fresh cold air into the exhaust to ignite this unburned fuel, this is the popping you hear.
If you were running just headers, you would see a sweet flame coming out too
You start out motorcycling with a full bag of luck and an empty bag of experience. The trick is to fill the bag of experience before you empty the bag of luck.
Some people are like slinkies; they're good for nothing but they still bring a smile to your face when you push them down a flight of stairs.
If your bike has an air induction system, thats the sound it makes when its working
After a high throttle application, when transitioning to off throttle, there is a lot of unburnt fuel that gets blown into the exhaust system. The air induction system pumps fresh cold air into the exhaust to ignite this unburned fuel, this is the popping you hear.
If you were running just headers, you would see a sweet flame coming out too
Trust me...I see the flame every time there's a louder pop. It's cool.
__________________ --In Life, Try To Be The Kind Of Person Your Dog Thinks You Are...
--Colts, 49ers, Lions, Detroit Red Wings, Detroit Tigers, USC Trojans, MSU Spartans, LSU Tigers
--2002 Kawasaki Ninja 250--SV-650 rear shock, Sonic Springs .80kg/mm front springs, ZX-2R graphics, flush mount front signals, tail pod rear signals, Kerker 2-1 race pipe, Factory Pro Stage 3 jet kit, UNI pod filters, ZG Double Bubble, Custom Creations soft vinyl seat cover, Kawi Green rim stripes, carbon brake fluid cap, carbon control levers, No Rear Fender, Yamaha R1 Style Mirrors, V-LEDs.com H4 HID Kit, Nelson Rigg Silver Streak Mini Saddle Bags, Rapid Transit Recon Tank Bag, Various Manufacturers Decals
So after getting in to pull out the other spark plug I noticed that one looked quite a bit more white than gray. From what I know, that means that it's running lean.
So, seeing as I do MOST (probably almost all, 90% or so) of my riding at high RPM, would I be correct in thinking that the culprit is the main jet?? I do my riding at high speed and high RPM because I mainly use the bike to commute on the highway. Very rarely is it being ridden with the RPMs below 6k. Now, because of this I'm guessing that the main jet is the part of the carb that is being used most often...and that since I'm running lean the main jet must be a bit too small.
Should I change out the main jet to a larger size and ride it around and check the plugs again soon, or should I just richen the whole thing from idle to top...bigger main jet, move the c-clip down a half notch...
And also, lastly, correct me if I'm wrong, but having an engine run a bit rich is better than having it running lean, right??
__________________ --In Life, Try To Be The Kind Of Person Your Dog Thinks You Are...
--Colts, 49ers, Lions, Detroit Red Wings, Detroit Tigers, USC Trojans, MSU Spartans, LSU Tigers
--2002 Kawasaki Ninja 250--SV-650 rear shock, Sonic Springs .80kg/mm front springs, ZX-2R graphics, flush mount front signals, tail pod rear signals, Kerker 2-1 race pipe, Factory Pro Stage 3 jet kit, UNI pod filters, ZG Double Bubble, Custom Creations soft vinyl seat cover, Kawi Green rim stripes, carbon brake fluid cap, carbon control levers, No Rear Fender, Yamaha R1 Style Mirrors, V-LEDs.com H4 HID Kit, Nelson Rigg Silver Streak Mini Saddle Bags, Rapid Transit Recon Tank Bag, Various Manufacturers Decals
Put a larger main in and after a run check the plugs. The main jet is not shut off in the idle position, it overlaps into the idle and midrange since it is a sloppy fit in the main jet circuit. To fatten the midrange place a shim under the needle. Make sure the shim is flat, if not flaten with hamer before you install.
I said running a bit rich is better than running lean...
Then you said...No, running a bit rich is better than running lean...
__________________ --In Life, Try To Be The Kind Of Person Your Dog Thinks You Are...
--Colts, 49ers, Lions, Detroit Red Wings, Detroit Tigers, USC Trojans, MSU Spartans, LSU Tigers
--2002 Kawasaki Ninja 250--SV-650 rear shock, Sonic Springs .80kg/mm front springs, ZX-2R graphics, flush mount front signals, tail pod rear signals, Kerker 2-1 race pipe, Factory Pro Stage 3 jet kit, UNI pod filters, ZG Double Bubble, Custom Creations soft vinyl seat cover, Kawi Green rim stripes, carbon brake fluid cap, carbon control levers, No Rear Fender, Yamaha R1 Style Mirrors, V-LEDs.com H4 HID Kit, Nelson Rigg Silver Streak Mini Saddle Bags, Rapid Transit Recon Tank Bag, Various Manufacturers Decals
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The way my JDjetting kit described the range of effect on the different parts of the carb are as follows:
pilot jet closed-1/4 throttle
needle 1/4-3/4 throttle
main jet 2/3-full throttle
If its popping at high rpm throttle off its your pilot jet....but I wouldn't mess with that.
My dirtbike pops constantly....and it runs GREAT. Unless its absolutely excessive backfiring and you start noticing a performance loss I wouldn't mess with it.
I just noticed that you already have a jet kit. You are fine. Don't overthink it.
Engine Popping On Deceleration...
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