This is why it sounds like potato potato

[Zip]

It was interesting reading all the replies of mixed knowledge...

Under Carburetor Environment:

Dual Fire Ignition = Potato - Potato - Potato

Single Fire Ignition = Spud - Spud - Spud

[twolazy]

First let me say that I love threads such as this -

Those old british bikes, Triumphs, BSAs, Nortons, Matchless, Royal Enfield etc used what we used to call "virtical twins" (500, 650, 750 and 850 displacements). While each cylinder had its own crank throw, it was a 360 degree crank, that is both pistons hit top dead center at the same time although each was on a different part of the cycle, i.e. one pistion was on the intake stroke, the other would be on the power stroke. This smoothed things up somewhat, moreso than the V-Twin, but the british vertical twins could still give you a fair amount of vibration.

Someone had mentioned timing being something of a bear on the radial engines, you might wanna take a look at the Bugatti W-16 engine, you talk about some engineering, the guys at VW must have been on a high when they came up with the W configuration.

[Diz]

The radial engine chopper made me wonder if anyone had ever built a sideways mounted wankel powered bike?

http://www.youtube.com/watch?v=mGOKkIx2__w

http://www.youtube.com/watch?v=mGOKkIx2__w

[boog]

quick note, both pistons on a triumph move together but fire opposite each other there is minimal vibration because the pistons are counter-balanced by the flywheel to about 80 percent. this does however give a slight rocking motion front to back . harleys are tits but trumpets are the whole body

[Captn Tim]

BOOG you have an iron butt or a unique trumpet. I rode triumph trophy and bonnys since '70, finally went hog in '96. My last Bonny was a '78, new ones have a different bottom end; but the old ones had no center bearing in the crank. So at high performance levels, the crank actually FLEXED and the vibration was ridiculous. Still, it was a great bike - best handling and most versatile I ever enjoyed.

[fordman1920032003]

i love the way my 05 sounds, main reason i bought it. it makes a pretty good chick magnet too.

[Mr.Mow]

Originally Posted by chief

yes the used materials are also inherent to the sound of an engine.
perhaps a real guitar freak will explain this..

Oh dear god.. you really want to get into this?!!!!

Maple (eastern, rock?) vs ash (asian, swamp?) vs mahogany (honduran, african?), rosewood (indian, brazilian, african)...


hahaha..

[ferris oxhide]

This may or may not have any bearing on the potato potato sound...

I've had my ironhead for many years and over time have run different exhaust (always separate pipes, no crossover or 2 into 1), different carbs, mufflers, cams, magnetos and heads and have noticed, and wondered about, that the exhaust pulse from the front cylinder always seems stronger and steadier.

It's crossed my mind recently that when the rear cylinder fires and its piston starts its downward stroke it accelerates the flywheels and the front piston upwards over the last 45 degrees of its exhaust stroke; in other words some energy from the rear cylinder goes into "power assisting" the front cylinder's exhaust stroke.

On the other hand, when the rear cylinder begins its exhaust stroke, the front cylinder still has 45 degrees of its intake stroke to complete; no "power assist" available for the rear cylinder's exhaust.

After the first 45 degrees of the rear cylinder's exhaust stroke the front piston begins moving up on its compression stroke, and when the valves close the flywheel is putting energy into two kinds of pumping actions and must be slowing down. The fluctuation in crank speed would be more noticeable at idle, maybe helping exaggerate the uneven firing pattern.

I guess what I'm saying is the sound is more PUHtato PUHtato ("PUH" being the front cylinder exhaust event) and that emphasis adds to the sense of uneven cadence.

Whadya think, am I nuts or is this possible?