Exhaust backfire, popping when letting off throttle - Motorcycle Forum
User Tag List

 
LinkBack Thread Tools
post #1 of 28 (permalink) Old 04-26-2009, 08:37 PM Thread Starter
Senior Member
 
SHTF Rat's Avatar
 
Join Date: Nov 2008
Location: New Hampshire
Posts: 317
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
Exhaust backfire, popping when letting off throttle

I notice that when I am accellerating, if I let off the throttle, my exhaust backfires and pops.

What causes this?

My muffler is not packed and has no baffles. Idle is 1500rpm. I never have popping or backfire during idle, cruising speeds or under accelleration. Only time I'm getting it is if I open up throttle to speed up rapidly, then let off throttle.

Is this damaging to my engine?

It's like a rapid succession of pops/bangs... like 3 to 5 of them.. Or is this its normal sound?
SHTF Rat is offline  
Sponsored Links
Advertisement
 
post #2 of 28 (permalink) Old 04-26-2009, 11:45 PM
Bikes, Guns and Video Games - Ain't life grand?
 
Jethrol's Avatar
 
Join Date: Sep 2007
Location: Oklahoma City
Posts: 601
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
I have the same problem. However, I've also noticed the backfiring when I decelerate from highway speeds without pulling in the clutch lever, just letting the engine spin down.

I talked to a friend of mine that knows a LOT about engines n stuff and he said it was not damaging to my engine.....just some extra gas that didn't get burned and ended up in the pipes and due to the heat of the pipes ignited making the POP.

I'm not sure how true that is but sounds reasonable.

2008 - Harley Davidson - Cross Bones (FLSTSB)
2003 - BMW - R1200C
Jethrol is offline  
post #3 of 28 (permalink) Old 04-27-2009, 01:06 AM
Administrator
 
Dodsfall's Avatar
 
Join Date: May 2008
Location: Illinois, USA
Posts: 22,936
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 110 Post(s)
 
Check your plugs to be sure the fuel mixture is correct. You can damage the engine by running too lean or rich.

2008 XL1200R

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Dodsfall is offline  
Sponsored Links
Advertisement
 
post #4 of 28 (permalink) Old 04-27-2009, 01:59 PM
Master At Arms
 
MlgWhiteboy's Avatar
 
Join Date: Apr 2009
Location: Layton, Utah
Posts: 109
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
Quote:
Originally Posted by Dodsfall View Post
Check your plugs to be sure the fuel mixture is correct. You can damage the engine by running too lean or rich.
x2 I also found this posted on the forum you might find it useful its a breakdown about spark plug wear.http://www.dansmc.com/Spark_Plugs/Sp...s_catalog.html

98 VTR1000F
MlgWhiteboy is offline  
post #5 of 28 (permalink) Old 04-27-2009, 06:25 PM
Senior Member
 
Prodigy's Avatar
 
Join Date: Jan 2009
Location: Miami
Posts: 610
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
this happens in bikes with carburetors, not fuel injected, maybe you need to see if it's tuned right...
Prodigy is offline  
post #6 of 28 (permalink) Old 04-27-2009, 06:39 PM
Senior Member
 
super32's Avatar
 
Join Date: May 2008
Location: sacramento, ca
Posts: 473
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
Quote:
Originally Posted by Prodigy View Post
this happens in bikes with carburetors, not fuel injected, maybe you need to see if it's tuned right...
uh oh... my FI does this too.
I was told something similar to what Jethrol said... which makes sense to me. I heard that MC's are a little more inefficient at burning gas? no?

popping only started to occur after I removed the baffle from my stock muffler. I also told that the "popping" was always there and that the muffler (in its entirety) muffled the "popping".

2005 Suzuki SV650n
Ride Fun, Ride Free, Ride Safe.

Last edited by super32; 04-27-2009 at 06:41 PM.
super32 is offline  
post #7 of 28 (permalink) Old 04-27-2009, 06:54 PM
Administrator
 
Dodsfall's Avatar
 
Join Date: May 2008
Location: Illinois, USA
Posts: 22,936
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 110 Post(s)
 
It's a matter of degrees. Large pops can signify a mixture that's way off, while some bikes may pop a little at peak efficiency.

Removing the baffles will generally require a jet change or remap. Performance is hindered or engine damage can occur if it's not done properly.

The easiest way to gauge is by checking plugs. If you want to get it perfect, you should use a dyno or use data taken from a dyno with your exact setup from a reliable source.

2008 XL1200R

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by Dodsfall; 04-27-2009 at 06:56 PM.
Dodsfall is offline  
post #8 of 28 (permalink) Old 04-27-2009, 07:08 PM
Senior Member
 
Prodigy's Avatar
 
Join Date: Jan 2009
Location: Miami
Posts: 610
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
Ok my mistake, I thought popping was due to bad fuel mixture... since FI motorcycles are controlled by a computer I thought that it wouldn't apply.... well I've learned something!
Prodigy is offline  
post #9 of 28 (permalink) Old 04-27-2009, 07:38 PM
Administrator
 
Dodsfall's Avatar
 
Join Date: May 2008
Location: Illinois, USA
Posts: 22,936
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 110 Post(s)
 
Changing things like reducing the exhaust back pressure or reducing the intake pressure will confuse the computer. It's assuming a certain fixed amount of air in and exhaust out in order to mix the fuel correctly.

2008 XL1200R

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Dodsfall is offline  
post #10 of 28 (permalink) Old 04-27-2009, 09:59 PM
Super Moderator
 
Eye_m_no_angel's Avatar
 
Join Date: Apr 2009
Location: Daytona Beach, FL
Posts: 15,469
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 478 Post(s)
 
Diagnosing problems via the Internet can be almost impossible at times, but Dodsfall nailed it right on as far as I can think. Remove the baffles and you increase airflow through the engine, and you have a lean condition. Once you re-jet, (assuming we're right) and things are running right, do what he suggested and check your plugs AGAIN. You may need to change the plugs to another heat range.

Also, for what it's worth, I've seen a similar type of popping symptom that was the result of a defective electronic ignition module on a carbureted bike.
Eye_m_no_angel is offline  
post #11 of 28 (permalink) Old 04-27-2009, 10:01 PM
2007 Yamaha Road Star Silverado 1700
 
primalmu's Avatar
 
Join Date: May 2008
Location: Tucson, AZ
Posts: 4,607
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 28 Post(s)
 
Garage
I've heard so many bikes pop on deceleration that I thought it was normal. As long as it doesn't hurt the engine, I say keep it... I kinda like the sound anyway.

Current:
2007 Yamaha Road Star Silverado 1700
1984 Honda Gold Wing GL1200 (stripped) - Project

Previous:
2003 Suzuki Bandit 1200 (naked)
2005 Suzuki Bandit 1200 (faired)
1998 Suzuki Marauder 800
2003(ish) Suzuki Katana 600
1984(ish) Kawasaki KZ550
2003 Suzuki GZ250
primalmu is offline  
post #12 of 28 (permalink) Old 04-28-2009, 12:31 PM
Senior Member
 
super32's Avatar
 
Join Date: May 2008
Location: sacramento, ca
Posts: 473
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
Quote:
Originally Posted by Eye_m_no_angel View Post
Diagnosing problems via the Internet can be almost impossible at times, but Dodsfall nailed it right on as far as I can think. Remove the baffles and you increase airflow through the engine, and you have a lean condition. Once you re-jet, (assuming we're right) and things are running right, do what he suggested and check your plugs AGAIN. You may need to change the plugs to another heat range.

Also, for what it's worth, I've seen a similar type of popping symptom that was the result of a defective electronic ignition module on a carbureted bike.
So, this "re-jetting"... is that expensive? difficult? specialized work? or is it a DIY thing over the weekend?

2005 Suzuki SV650n
Ride Fun, Ride Free, Ride Safe.
super32 is offline  
post #13 of 28 (permalink) Old 04-28-2009, 12:34 PM
Administrator
 
Dodsfall's Avatar
 
Join Date: May 2008
Location: Illinois, USA
Posts: 22,936
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 110 Post(s)
 
Quote:
Originally Posted by super32 View Post
So, this "re-jetting"... is that expensive? difficult? specialized work? or is it a DIY thing over the weekend?
It involves removing and at least partially disassembling the carbs. Depending on the bike, it can be fairly expensive to have done. If you are comfortable around wrenching, it's totally do-able over a weekend.

2008 XL1200R

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Dodsfall is offline  
post #14 of 28 (permalink) Old 04-28-2009, 12:38 PM
Administrator
 
Dodsfall's Avatar
 
Join Date: May 2008
Location: Illinois, USA
Posts: 22,936
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 110 Post(s)
 
I probably should add that the ECM needs to be reprogrammed or replaced in an EFI bike, since there are no carb jets involved with those. Aftermarket modules such as a Power Commander are fairly popular for this, since they can be bought for about the same price as a single adjustment to the computer at a dealer. (About $200-$300)

2008 XL1200R

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Dodsfall is offline  
post #15 of 28 (permalink) Old 04-28-2009, 09:49 PM
Super Moderator
 
Eye_m_no_angel's Avatar
 
Join Date: Apr 2009
Location: Daytona Beach, FL
Posts: 15,469
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 478 Post(s)
 
"So, this "re-jetting"... is that expensive? difficult? specialized work? or is it a DIY thing over the weekend?"

On my bike (HD) it's about a 30 minute job if I stop for a cup of coffee and a cigarette. (Not counting running checks and plug evaluation.) I have heard that some of the metric bikes however, can be real nightmares to get the carbs off, but I have no experience working on them. The concept itself, is very easy.
Eye_m_no_angel is offline  
post #16 of 28 (permalink) Old 04-29-2009, 05:48 AM
Honk if you've never seen a gun fired from a bike
 
Jay550's Avatar
 
Join Date: Dec 2008
Location: Collegeville, PA
Posts: 822
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
Backfiring happens all the time, in cars and bikes, you just don't hear it because the muffler/exhaust. Since you've modified it, now you do. What it is, is incomplete combustion, fuel is left over, and shot into the exhaust pipes. The heat from the pipes then ignites the vapor and boom, backfire. Not uncommon, should happen when decelerating in gear, the explosions aren't as violent, and don't get as much gas burned, so left-overs happen.

If you have it happening at times other than when you are decelerating, then yes, you are running to rich and need to adjust that, or you should perhaps check your timing, you might be experiencing detonation, which can sometimes not burn allt he fuel up, as it fires to early preventing the peak and optimal explosion.

2001 Yamaha Roadstar

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Jay550 is offline  
post #17 of 28 (permalink) Old 05-04-2009, 10:41 PM
Verified
 
treecutter's Avatar
 
Join Date: Apr 2009
Posts: 21
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
popping

my vulcan has always popped a little on deceleration since the day I brought it home from the dealership im pretty sure some popping is normal since im all stock and the bike is still running well after 8 or 9 years that's aweful im questioning how long I've had the bike oh well its popped for ar least eight years and yes it does sound cool
treecutter is offline  
post #18 of 28 (permalink) Old 02-19-2014, 02:15 AM
Registered
 
Join Date: Feb 2014
Posts: 2
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
check the spark plug..
mhdchehade is offline  
post #19 of 28 (permalink) Old 02-19-2014, 07:18 AM
Banned
 
Join Date: Jul 2013
Location: Central USofA
Posts: 916
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
So many things it could be, a lot depends on what model motorcycle.

Too lean, as mentioned, is generally the cause. A vacuum leak is not uncommon.

Plugged slow jets not uncommon (and that can cause other major problems. If the bike never did it, sat a long time and started popping, that's more of a possibility).

Incorrect air screw settings can sometimes cause it, I've been able to tune it out (or hide it..) with an air screw adjustment in some cases.

Many bikes have a emission control system (PAIR, for example) that injects air into the exhaust, sometimes removing/blocking these corrects the issue.

Then, some people like it, and learn to get really good at making the POP loud, optimized. It can be a lot of fun at other people expense, which in the big picture, is not true fun at all.......
SR71 is offline  
post #20 of 28 (permalink) Old 02-19-2014, 08:45 AM
It hurts when I pee
 
arntufun's Avatar
 
Join Date: May 2011
Location: Upstate, NY
Posts: 1,058
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
Popping on decel is a lean condition. Many things can contribute to a lean condition as noted above, but two other possible causes not mentioned are

1. exhaust gasket leak
2. a free flowing (performance) exhaust


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
arntufun is offline  
post #21 of 28 (permalink) Old 02-19-2014, 08:58 AM
Rough Writer
 
NordicMan's Avatar
 
Join Date: Feb 2014
Location: Ontario Canada
Posts: 1,106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 15 Post(s)
 
Quote:
Originally Posted by mhdchehade View Post
check the spark plug..
I'm hoping "5 years later" the guy who originally started this topic has figured out the problem

But yeah if you alter the exhaust backpressure by either swapping out the pipe for an aftermarket one or by removing the factory baffles/restriction, then you need to either rejet (carb) or adjust the ECU (if fuel injected)
NordicMan is offline  
post #22 of 28 (permalink) Old 02-19-2014, 09:53 AM
Super Moderator
 
Eye_m_no_angel's Avatar
 
Join Date: Apr 2009
Location: Daytona Beach, FL
Posts: 15,469
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 478 Post(s)
 
"I'm hoping "5 years later" the guy who originally started this topic has figured out the problem "

LOL!
Eye_m_no_angel is offline  
post #23 of 28 (permalink) Old 02-19-2014, 10:33 AM
Road Captain
 
Bob Mears's Avatar
 
Join Date: May 2012
Location: Texas
Posts: 78
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
 
And no one mentioned that the spark plug also fires on the exhaust stroke too. That also contributes to the popping.
Bob Mears is offline  
post #24 of 28 (permalink) Old 02-19-2014, 03:38 PM
Registered
 
Join Date: Feb 2014
Posts: 2
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
of course he did but there some people that are googling for solution just like me
mhdchehade is offline  
post #25 of 28 (permalink) Old 02-20-2014, 10:06 AM
FTW ┌∩┐(◣_◢)┌∩┐
 
Kaz71's Avatar
 
Join Date: Dec 2012
Location: NW NJ
Posts: 1,691
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
There is no adjustment for a FI ECU. The OE ECU is preset and runs according to OE build of engine. You can get a power commander and have it programmed to correct settings or get a power pro commander (CVT) continuous variable tuning which self adjusts to changes in air/fuel mixture. Nice unit made by Cobra but does cost more then a power commander. Easy install all plug-n-play.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

2011 VN1700 Classic
Cobra speedster slash downs
Cobra Fi2000 PowrPro Tune
Floorboard foot pegs
Kuryakyn flamed floorboard covers
Mustang seat studded
Dark smoke wind screen
Chrome radar detector mount
K&N air filter
Wolo Bad Boy chrome air horn
HID head light
Kaz71 is offline  
post #26 of 28 (permalink) Old 02-20-2014, 10:36 AM
Cyborg in training
 
trixter's Avatar
 
Join Date: Oct 2010
Location: Sacramento
Posts: 950
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
Quote:
Originally Posted by super32 View Post
So, this "re-jetting"... is that expensive? difficult? specialized work? or is it a DIY thing over the weekend?
I did a ninja 250 a couple years ago, if you know what jet sizes you need (pilot and main usually) and whether or not you need any needle shimming you can order just what you need and that is often $5/cylinder or less. If you dont know what you need you may have to buy a set of jets and experiment ultimately not using most of the set. That can increase the cost.

http://www.dynojet.com/jetkits/ has a lot of kits for a lot of bikes that come with several jets so you can get exactly what you need.


The jets themselves are often (always?) brass the only specialized work is uncrewing them without marring the brass. This is not hard if you use the correct sized screwdriver and take your time. Oh and inspecting to make sure you dont have any insect parts in the carb bowls before final reassembly :P

You might have to adjust the idler screws which on some are capped because of emissions controls. This is not hard to do either, usually you drill the plugs out just go really slow with the drill to avoid punching through to what is underneath.

Since you will probably remove the carb to do this work you might as well sync it or at least check the sync to see if it needs any work.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
trixter is offline  
post #27 of 28 (permalink) Old 02-20-2014, 10:38 AM
Cyborg in training
 
trixter's Avatar
 
Join Date: Oct 2010
Location: Sacramento
Posts: 950
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
 
Quote:
Originally Posted by Eye_m_no_angel View Post
"I'm hoping "5 years later" the guy who originally started this topic has figured out the problem "

LOL!
I am bad about reading meta data I just recall seeing this thread pop up a couple times and figured I would read it. doh!


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
trixter is offline  
post #28 of 28 (permalink) Old 02-20-2014, 11:02 AM
Super Moderator
 
Eye_m_no_angel's Avatar
 
Join Date: Apr 2009
Location: Daytona Beach, FL
Posts: 15,469
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 478 Post(s)
 
No worries. Like the guy said, somebody else might get something out of it even though the original poster solved his problem long ago.


(Unless, of course, he's still staring at it and scratching his head.)
Eye_m_no_angel is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Motorcycle Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome