Evo backfiring a bunch...

How many ideas can someone suggest for me to figure out why my evo (96 wide glide) pops like crazy on decel?

Right now it has the stock breather but I do have an SE breather I could put on.

It has what I believe is a thunderslide in the carb with "adjustable" mixture. ??

It has drag pipes with no baffles. I have some SE pipes complete I could put on and they have baffles.

The bike runs like a watch. Starts, idles, runs, accelerates, etc. wonderfully.

The only issue I have with it is this non-stop popping on decel. Sounds to me like it's coming out the exhaust. (Technically not a backfire.)

The carb was just off and was "tuned" by an indy. It just pops like crazy on decel otherwise there is no problem.

Any ideas? I've lost some confidence in this indy.I'll try all...

Thanks!

 

Decel pop is caused by a too rich or too lean mixture, exhaust or intake leak, improper plug gap/fouled plugs and maybe timing. Drag pipes without baffles may never stop decel popping completely. Unless you run in the top end all the time, get rid of the drag pipes, you will get more bottom end and it will sound better. Put the SE pipes and air cleaner on, jet it properly, adjust the idle circuit, seal up all the exhaust/intake leaks and it should run like a scalded dog.

 

If the throttle isclosed on decel, and it pops, stumbles, bucks, back fires, etc., the usual cause is a lean condition, such as a too lean pilot jet and/orlean idle air mixture.Since the bike goes so well otherwise, my first move would be to carefully dial in the idle air mixture, maintainingan idle speed of 900-1000 RPM's. Note how many turns out from lightly seated the adjustment is now, then also where it ends up where best running occurs.Once roughed in by ear for best running, make small, singleadjustments, then road test. Idle to 2000 rpm's is where the idle mixture affects running. I'd also ask the tuner what exactly he changed on the carb. I recommend writing everything down if your memory is like mine. It would be great if you would update us.

 

JB,
If you were not having any problem before and based on the fact that an Indy messed with the carb, that is where I would start [:@]. I'm not a CV guy as I run an S&S and can't offer any help there. My guess is maybe an intake leak, the drag pipes themselves with no bafflingorthat the mixure adjustment, jetting and/or needle is set incorrectly. My game planwould be to return it to thatIndy and have him get it right atN/C to you. A reputable shop will not have a problem taking a looksee and doing that.

I would get it right before you throw any otherparts into the mix. Normally changing to a free breathingair cleaner and exhaust system requires some carb tuning.Not knowing where you are now will only complicate the problem and sorry that I can't offer more help. When you get it figured out witha baseline on where the carb is at,plenty of guys here can help with how to reset the carb up with the parts that you wish to install.Good luck and keep us posted.

 

Most exhaust backfires are caused by leaks in the exhaust system. check for a leak by the head (you did change the exhaust seal, when you put the pipes on, right?)

 

Do you get the popping when you blip the throttle at idle and the revs are settling back down? If so, then blip the throttle as you spray water around theexhaust flanges on the head. If the bike stops popping and idles smoothly, then you have an exhaust leak (the water effectively cools the exhaust gases and stops them igniting in the exhaust). If it makes no difference then I would say that you have a jetting problem.As mentioned above, get rid of the "drag" pipes and install the SE pipes. You need the backpressure the baffled pipes provide because the EVO doesn't have anti-reversion steps built into the heads. This means that returning exhaust gaspulses re-enter the combustion chamber and polute the fresh mixture which reduces your power output.
You will probably find that once you put the SE pipes and air filter on, your bike will be running lean anyway and will need to be re-jetted.

Hope this helps and let us know how you get on.

 

Hey guys, thanks so much for all the good tips. I will try out absolutely everything this weekend and report back.

JB

 

If you have drag pipes they are going to pop . That is the nature of the beast . You can tune the pop out a little bit . Not trying to be a smart butt but if you are some where you don't want it to pop (comeing home late at night ) pull the clucth in and it want pop any more .

 

I've an an 85' softail with drag pipes on it also pops on decel.....I love the sound of my drag pipes. I've tried other pipes but they make a harley sound like a honda!!

 

Here's an old racers trick to tune in the drag pipes and take out the 'dip' in the torque curve. Works like champ on my 94 fxstc!

http://www.nightrider.com/biketech/exhaust.htm