Author Topic: Custom Exhaust For my B6 StreetFighter Decel Crackle (Read 4023 times)

osmckeown · « **on:** February 21, 2007, 03:01:39 PM »

I just got this thing from a guy and he said it has a jet kit in it, it pulls pretty good and wheelie's in first without clutch'n it no problem, so I believe him. My buget is low so I cut the stock can off, and welded a 2" automotive glasspack on the stock piping. After welding a bracket and polishing it looks and sounds really good, for only $30, you can't beat that. I actually had to replace my clutch, with the added power it kept slipping around 8-9K RPM, keep in mind the old clutch was bad, with only 9K on the engine this guy was ragging on it, the friction plates were almost smooth as glass. *Tip, DON'T get the 10% stiffer springs you will get to the first stop light and wish you never put them in* The only problem is now that there is more air flow I get a little bit of a decel crackle/pop/poof/ping when rolling off the throttle at a high RPM. I mean it's not a huge BANG or anything just little poofs and pings. As if it's running a little lean. I took the tops of the carbs off and put the needles on the lowest clip setting (5th notch) and this helped a little, but is there a way to tune the idle mixture without having to change jets to get the backfiring to stop? Thank you in advance, -Jim

Red01 · « **Reply #1 on:** February 22, 2007, 10:07:18 AM »

Minor decel popping is normal. The stock can just did a better job of covering it up.

osmckeown · « **Reply #2 on:** February 22, 2007, 02:36:49 PM »

My only Q is that when it's popping on decel is that if I put the choke on (ever so slightly) it will stop popping on a decel no matter what RPM.

chupacabra · « **Reply #3 on:** February 22, 2007, 05:33:43 PM »

Turn your air/fuel screw out a little and see if that helps you.

pmackie · « **Reply #4 on:** February 23, 2007, 02:27:13 AM »

Quote

is there a way to tune the idle mixture without having to change jets to get the backfiring to stop?

As chupacabra said, the pilot air screws can be adjusted to richen up the mixture slightly from closed to 1/4 throttle openings. If there was a jet kit installed, they should have had the factory "plugs" drilled out and removed, so you can adjust. Try 1/2 turn at a time and see how it feels.

osmckeown · « **Reply #5 on:** February 23, 2007, 03:21:23 AM »

Thanks I'll give it a shot guys, and I'll post pics of the exhaust.

gsxr400 racer · « **Reply #6 on:** February 24, 2007, 08:54:42 PM »

your heavy clutch springs alternate stock stiff stock ect... and you'll be dandy like a lion mate!

Dazbandit · « **Reply #7 on:** March 23, 2007, 09:32:28 AM »

Is the bandit a secong gen bandit?They all pop on decel.The p.a.i.r system injects a little air into to exhaust ports causing the unburn fuel to burn hence the backfire or pop.Also with an aftermarket can you can hear this more.
Hope this helps but its hard to say without hearing how bad your bike is.

wiredgeorge · « **Reply #8 on:** March 27, 2007, 12:16:10 AM »

Unburned exhaust is recycled into reed valves. This allows COLD AIR in... pop pop pop... common on ALL reed valve smog head equipped bikes. The reed valves are flaps. The flaps open when actuated by a vacuum switch. The vacuum switch is connected to your carbs. The reed valves are typically atop a valve cover on a 4 cylinder and down on the cylinders on a V-Twin. OK... first order of business is to get rid of this junk unless you need to be emissions certified or tested. If you are, I suspect that it would just as effective to temporarily lean your air/fuel mixture.

To get rid of the emissions control stuff and a lot of the decel popping (which is worsened by putting a freer flowing muffler on), do this:

1. There is a big hose with a tee fitting on your valve cover. Remove the hoses. They lead to a vacuum switch. remove the vacuum switch. There are two hoses; probably coming off the #1 and #4 carbs that go into a tee fitting. These are vacuum hoses... get rid of them too... OK to plug a few things up, there will be a hose going to the airbox from the reed valve hoses. Plug this opening. Since there are passages under the reed valves going down to the exhaust runners right next to the combustion chambers (where the stuff is to be burnt that doesn't end up in your air box), put some RTV BLACK in the holes. They don't get all that warm and this works fine OR you can connect a hose between the two spigots where the hoses went on the valve cover OR you can cut some blank plates but let the reed valves sit where they are and any gaskets to keep this area sealed. The blank plates can be cut from aluminum stock and use some gasket maker to seal these to the valve cover. This looks better than leaving the snouts in place. APE racing likely makes billet plates; not sure for the Bandit. These plates are called "coasters". OK... you got rid of all the emissions junk and there is yet one more thing... the two vacuum spigots on the #1 and #4 carbs... put 7/32" vacuum caps on these. If not capped, they create air leaks in the carb venturis and you will not get the bike to idle.

This system has been used for almost 20 years now and doesn't do much for performance except create decel backfires. The other thing that should be done is install 1 size larger pilot jets and adjust the mixture screw OUT until the backfiring is toned down. With an open pipe or the car glasspack, it will likely never go away completely. There are also exhaust gaskets that might be leaking. Put in new gaskets each time the pipes are removed and retighten the nuts that hold the pipe flanges after a few hundred miles. If there are not lockwashers under the nuts, these help keep them tight.

Dazbandit · « **Reply #9 on:** March 27, 2007, 05:48:55 AM »

There are many places on the webb that show you how to get rid of the P.A.I.R system specific to the bandit.
You can easily make your own block off plates for the ports.

Please note the system does not affect the preformance of your bike.I like the exhaust pop and choose to keep it on HEH HEH.

osmckeown · « **Reply #10 on:** March 29, 2007, 02:29:37 PM »

I don't have a PAIR system on the bike, I'm here in Florida. The carbs are stock I found out, haven't drilled out the pilot plugs to adjust the idle mixture screw. I did notice that I didn't put the midpipe all the way tight in the collector, after doing this the "POP" decreased alot. Still, however I also cut the end of the glasspack and welded a piece of pipe back on at an angle so it points straight back instead of up to the sky and this helped alot. Pointing the exhaust made it alot quiter to me, the driver, and alot of vibrations were gone. I don't think I'll ever buy another aftermarket pipe since all it's just a glasspack essentially with a fancy cover, mine looks like chrome, for $30, can't beat that! I could put a reducer in it for more low end torque, just like the after market ones have, but I still wake up the neighborhood at 3am!

Red01 · « **Reply #11 on:** April 01, 2007, 09:44:22 PM »

When do we get to see a picture (or more) of your handiwork?

Red01 · « **Reply #12 on:** May 28, 2007, 03:36:45 PM »

Any pix yet?