Bonneville America Forums Forums Technical Forums Exhaust "Popping" on Deceleration

Who can explain the "popping" on deceleration? I have the AI removed, and 2 stages out of the rear of my stock exhaust, and the snorkel out...but nothing else has been done to the bike..19,000 miles now...Im hearing that its a "lean" mixture, but I always thought that a "rich" mixture would cause this by putting too much gas into the exhaust....confused...I like the "pop", but want to correct if it's not a good thing for the bike...Pops louder after warm...

ok here we go again...a PROPERLY tuned motor with high performance pipes WILL POP in DECEL....

From the mikuni site....

Note: 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.
One thing that should be pointed out is that while the throttle may be
closed, leaning up the mixture, and it may take several revolutions of
the engine to build up a burnable mixture in the pipe, the engine will
still be running at a high enough RPM for the ignition advance curve to
be advancing the ignition. So, if you have an ignition system that
fires a waste spark, it's going to fire that spark during the valve
overlap period on one of your four cylinders, and that's enough to make
the exhaust backfire.



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.

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.


your engine, rather because it is an indication of lean and running so
can burn your exhaust valves everyone thinks it to be a bad thing.

Tuning your bike richer means an excess of fuel and very little to no
oxygen. Thus the unburned fuel passes through the pipe without ever
igniting. So you can think of the popping as a sort of environmental
control on your bike, combusting excess fuel that would have otherwise
not gotten burned.

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So the "popping", to me, is not only cool, but harmless? I will keep her that way, 'cause she runs REALLY sweet...

Oh great, they mention the "pop" and the "crackle" but nothing about the "snap".

Lola flatulated embarrassingly loud on decel , back out your screws a smidge and that will fix it , she just makes a nice demure rumbly popping now , just enough to proclaim " I am strong I am invincible I am Woman " she likes that song . Carley Simon ?

Quote:

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" I am strong I am invincible I am Woman " she likes that song . Carley Simon ?

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Helen Reddy

i had the "poping" noise on my 04 america as I was crusing on the hiway one day found out that a plug from the carb came off and the others where cracked, replaced them no more pop (mod pipes carbs jeted, no ai.)hope it's that simple for you!

I Agree I like the "after rumble" I have it since I got rid of the AI and pulled the 1st baffle. As long as its not hurting anything I see no reason to change it.

OK so the leanness isn't really a leanness at idle or early aceleration (a leanness you would want to fix), just the result of the air being sucked at decel while the throttle is closed?

I don't get a "rumble". I occasionally get one very loud POP on decel.