 popping
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Joined: Dec 2005
Posts: 371 Likes: 2
Adjunct
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OP
Adjunct
Joined: Dec 2005
Posts: 371 Likes: 2 |
Hey all. Just installed epcos and it is popping on deceleration. I like the noise but I thought I would check out any potential problems. I have the AI removed and have not re jetted the carbs.
Any ideas.
Cheers
A dog, a bike, a ute,
Now in the deep south.. Newcastle.
Cold winters, cold rain
Come on summer
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Re: popping
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Joined: Sep 2008
Posts: 3
Complete Newb
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Complete Newb
Joined: Sep 2008
Posts: 3 |
Just installed ss short slashed pipes.Same problem,popping on deceleration.Had th AI removed.rejetted,snorkel removed & shims done. Now sounds great and performs better.Only problem,keep an eye out for the boys in blue,they don't agree how great she sounds now
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Re: popping
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Joined: Aug 2005
Posts: 2,726
Loquacious
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Loquacious
Joined: Aug 2005
Posts: 2,726 |
It is normal for less restrictive pipes to have decel popping that wasn't there with stock pipes. Very loud popping, including popping while shifting, can be improved by adjusting the pilot screws (out) or changing the pilots to next larger size. Keep in mind that if you eliminate popping with the pipes you have, you will most likely be running way too rich.
Bob
2005 America, 904cc - sold. 2014 Trophy SE.
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Re: popping
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Joined: Feb 2007
Posts: 23,227 Likes: 62
Fe Butt
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Fe Butt
Joined: Feb 2007
Posts: 23,227 Likes: 62 |
You should have more of a rumble on decel with less restrictive pipes. Excessive popping or backfire can indicate a lean condition but it can also indicate an exhaust leak. If you put less restrictive pipes on with no jetting or adjustments you are probably lean. If the stock air box is still in place and not changed you can probably go up a size on the main (depending how open your pipes are you may not need to) and adjust the pilot screw.
I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!
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Re: popping
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
Quote:
It is normal for less restrictive pipes to have decel popping that wasn't there with stock pipes.
This hasn't happened to me on any vehicle I've ever owned. That includes my current bike w/TORS, two four-cylinder bikes that I changed to straight-through Kerker headers, and many small and large block Corvette motors. What's the root cause?
Jack
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: popping
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Joined: Jan 2006
Posts: 3,606 Likes: 2
Loquacious
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Loquacious
Joined: Jan 2006
Posts: 3,606 Likes: 2 |
first posted some years ago most recently April of 07...so I guess now is a good time to repost... Quote:
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.
THE VOICE OF REASON
per: Stewart
AF&AM/Shriner/Scoutmaster
130/45 TBS 2shim SS Uni 18/42
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Re: popping
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
Quote:
So, if you have an ignition system that fires a waste spark, it's going to fire that spark during the valve overlap period
Our bikes don't do that, do they? Of course, that doesn't explain why my older bikes never popped. From what I remember, it was common to fire a waste spark on inline fours.
BTW, thanks for posting. Hadn't see this writeup before.
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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