Motorcycle Repair: Exhaust back fire, 1600 meanstreak, stock pipes

Question
Hi Wayne;
I have an '05 Kawasaki 1600 Meanstreak.  Bought it new.  Put on V&H Big Shot pipes about 3 years ago.  Power Commander was also installed.  Bike was run on dyno.  All checked out fine.  Well, it continues to backfire upon backing off on throttle, unless done quickly.  A return to dyno gave the same results...all is supposedly o.k., with no apparent exhaust leaks.  The bike runs fine and sounds great...except for the back firing.  What's up with that?

Answer
Hi Ken,

There are a few reasons for backfiring.
Some decel exhaust popping is normal in these
engines but is not normally noticable
with the stock exhaust system.

When you add a different pipe without the
baffling and backpressure the popping increases.
This is due to having less restriction in the
air flow in and out of the pipe.

The fresh air rushing into the pipe causes
the backfiring. There are some ways to deal
with this. The most obvious is using stock
pipes again which is not always desirable.

The second thing to do is to ensure that
you have no air leaks anywhere on the
pipe or muffler seams. The place where
the pipe seals in the cylinder head especially.
Any gasket leak will allow air to enter
the pipe and cause this afterburn popping.

The third thing having a rich enough mixture
to burn fully in the cylinder. If your fuel
is mixing on the lean side the fuel mixture
is reluctant to burn fully and some of it
enters the exhaust pipe.

The lean unburnt fuel builds up in the pipe
and then ignites when the fresh air hits it.

When you release the throttle suddenly you
are cutting off the fuel mixture which makes
it lean and so it fails to burn fully inside the
cylinder. It instead burns when it hits the pipe
and causes a backfire.

This problem is compounded by air injection systems
which add air to the exhaust gases to reduce pollutants.

So, your bike may do very well on dyno tests
but still run lean when you release the throttle
quickly. This is somewhat normal and can be
compensated partially by running a slightly
richer fuel mixture.

A bigger solution or result may be possible by checking
the air injection and blocking it off.

Here is some info on doing that:
http://www.gadgetjq.com/smogstuffremove.htm

So, block the air injection first, check for exhaust gasket
leaks and finally have the fuel mixture richened.
Last resort is again installing the stock pipes or pipes
with more baffling.

Good luck!
Wayne S.
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