Why do motorcycle engines idle unevenly?

Question

I have noticed that motorcycle engines tend to have an uneven rhythm while idling, as though a cylinder is misfiring. Is it that motorcycle engines have an asymmetric firing order? If so, what is the purpose of the asymmetry?

OK, I must be referring to Harleys, which also seem to idle loudly.

Answer 1

Yes: asymmetrical firing.. and NO, all 2 cylinder motorcycles are not made the same. Most older import bikes are side by side twins that do not share the common crankshaft pin as the Harleys and other newer "cruiser style" bikes do. Old-style import twins just go "put-put" evenly when they run. This makes for a smoother running engine. Harleys vibrate a lot and are usually mounted in rubber to isolate the engine from the chassis and the rider. )

HERE IS YOUR ANSWER!... (I did copy and paste)

The classic Harley-Davidson engines are two-cylinder, V-twin engines with the pistons mounted in a 45° "V". The crankshaft has a single pin, and both pistons are connected to this pin through their connecting rods.

This design causes the pistons to fire at uneven intervals, the consequence of an engineering tradeoff to create a large, powerful engine in a small space. This design choice is entirely vestigial from an engineering standpoint, but has been sustained because of the strong connection between the distinctive sound and the Harley-Davidson brand. This design, which is covered under several United States patents, gives the Harley-Davidson V-twin its unique choppy "potato-potato" sound. To simplify the engine and reduce costs, the V-twin ignition was designed to operate with a single set of points and no distributor, which is known as a dual fire ignition system, causing both spark plugs to fire regardless of which cylinder was on its compression stroke, with the other spark plug firing on its cylinder's exhaust stroke, effectively "wasting a spark." The exhaust note is basically a throaty growling sound with some popping.

The 45 degree design of the engine thus creates a plug firing sequencing as such: The first cylinder fires, the second (rear) cylinder fires 315° later, then there is a 405° gap until the first cylinder fires again, giving the engine its unique sound.

Attempt to patent the sound...

United States
In the United States, the test for whether a sound can serve as a trade mark "depends on [the] aural perception of the listener which may be as fleeting as the sound itself unless, of course, the sound is so inherently different or distinctive that it attaches to the subliminal mind of the listener to be awakened when heard and to be associated with the source or event with which it struck".

This was the fairly strict test applied by the US Trademark Trial and Appeal Board in the case of General Electric Broadcasting Co., 199 USPQ 560, in relation to the timed toll of a ship's bell clock.

More famously, Harley-Davidson attempted to register as a trade mark the distinctive "chug" of a Harley Davidson motorcycle engine. On 1 February 1994, the company filed its application with the following description: "The mark consists of the exhaust sound of applicant's motorcycles, produced by V-twin, common crankpin motorcycle engines when the goods are in use". Nine of Harley Davidson's competitors filed oppositions against the application, arguing that cruiser-style motorcycles of various brands use the same crankpin V-twin engine which produces the same sound. After six years of litigation, with no end in sight, in early 2000 Harley Davidson withdrew their application.

Answer 2

This Site Might Help You.

RE:
Why do motorcycle engines idle unevenly?
I have noticed that motorcycle engines tend to have an uneven rhythm while idling, as though a cylinder is misfiring. Is it that motorcycle engines have an asymmetric firing order? If so, what is the purpose of the asymmetry?

Answer 3

I think ur motorcycle engine have an asymmetric firing order. But I am not very clear. I advise u to get on a site called bikerkiss to ask for help. There are many motorcycle experts there.

Answer 4

Of all the different types of engine configurations MOST have symetrical firing orders except V twins. The asymetry (sp?) has no purpose it is just inherent in the design, sometimes, fortunately for Harley Davidson, it contributes to a pleasing engine cadence. Another factor to consider is that most cycle engines are in a much higher state of tune than the normal family sedan. Cam profiles that favor high performance tend to cause less smooth low end performance

Answer 5

Basically, the more cylinders there are, the slower and smoother the idle is, as it smooths out the firing. Compare a single cylinder to a V8 auto engine at idle.
Also, larger bores/strokes idle rougher, because of the more mass moving.

Answer 6

The only one I am aware of that idles unevenly is Harley Davidson. The reason is it's internal configuration. Hopefully someone else will explain in detail, I don't have the time now.
all the others are even, as far as I know.

Answer 7

Harley Davidson Firing Order

Answer 8

My honda 599 has a pretty smooth idle just a little erratic sounding due it's camshaft profile. My kawasaki kfx 700 vtwin runs very smooth at idle. My single cylinder kawasaki klr650 even runs smooth at idle. My uncles Harley runs like absolute sh*t at idle and loudly at that nor does it run well at speed with it's ridiculous vibrations and as someone mentioned earlier it's programmed misfiring's.

Answer 9

Harley's can be made to idle relatively smooth but customers don't want it. HD spent about 6 yrs trying to patent their sound (don't remember if they gave up or lost?)
The charge robbing at low RPM is the reason they sound like they do. If you fit dual carbs with separate intakes for each cylinder it sounds like a normal motor. HD even created a misfire on the fuel injected bikes so the sound would be the same as the carburettor ones and modified intake manifold so they cant run smoother a idle (now tell me HD owners ain't retarded????)

Answer 10

my Yamaha FZ6 idles smoooooth
I take the time to make a homemade manometer and adjust all 4 injectors
I don't like to brag, but I can make any bike run better and smoother than any factor trained motorcycle technician