Stroking the King
Words: Kirk Herbert

Nothing to do with the more obscure sexual habits of a certain Mr Presley but a description of a total performance upgrade for Harley-Davidson's Road King.

Why a Road King, you might ask? Surely there must be more likely candidates for this conversion.

Well yes, there is. Take the FXDX, for instance: light, agile, adjustable suspension and nice soft compound tyres, and having already carried out this conversion on an FXDX I found it to be extremely rapid in every sense of the word. Fun is the word I would use to describe that incarnation, but to qualify that statement I would say it was fun in the say way that borrowing a highly tuned race bike for the afternoon would be. Yes, it was a blast with the front wheel in the air and the rear wheel spinning as you changed into third gear, but I'm not sure I could live with that sort of urgency in everyday riding situations.

So needing to find a likely candidate that can harness all the power this conversion unleashes, a bike that can convert all that extra torque into all day useable power, the FLHR is the natural choice: a stable, well-balanced bike capable of translating what your right hand is doing into a language your rear tyre can understand.

Lets look at the hardware needed to carry out this conversion.

Firstly, and most importantly, is the stroked crankshaft. Stroked in this context effectively means a greater distance between the small end centre and the crank pin, giving you extra leverage. Think of it as sliding a tube over the end of a spanner to remove a seized nut, it's all about more turning force.

The increased length in this case is 3/8 of an inch taking overall dimensions to 4 3/8 of an inch, this combined with the 3 7/8 pistons and 1550 barrels give us an overall capacity of 103cui (1.7 litres?!?), and compression ratio is up to 10:1.

In layman's terms we have a deeper breathing motor, with a greater turning force.

The old adage goes "There ain't no substitute for cubes" and it still rings true, this lift in capacity allows the engine to do more work at less rpm, giving a less hurried, lazy feel to the riding experience.

To compliment this increase in torque, new camshafts are added, and the 258 lift Screamin' Eagle cams offer greater lift and added duration (effectively lifting the valve further off its seat for longer), giving the engine more punch throughout the rev range and, more importantly, holds on to the power for longer: useful in those situations where you find yourself halfway through overtaking something when another something comes the other way. That's the time you don't want to fall off the end of the power curve: the uprated cams will keep you pulling all the way to the redline.

The revised Screamin' Eagle cylinder heads have redesigned, flow-tested port shapes to speed up the flow of mixture, and the bath tub combustion chamber is to retained to ensure good burn rates, and an even flame front.

Induction is the next area to look out and in my opinion there is only one carb to consider: the flat slide Mikuni. This carb has been around in different guises for years and is always the first choice for people looking for instant response and good driveability. Back in the old days, the complaint most levelled at the Mikuni was its perceived heavy throttle action, but not any more, a roller bearing now ensures that the action is smooth and surprisingly light. This carb stands alone in offering a bolt on solution to people who need a little more urgency than the stock 40mm CV can offer.

Don't get me wrong the stock carb is a very capable unit when correctly jetted and is adequate for most applications but it will never match the flat slide for instant response. Open the throttle on your CV carb and while you wait for the vacuum to lift the slide and the fuel to be delivered, the guy with the flat slide has already gone, quicker than John Leslie leaving the "This Morning" studios.

The 45mm Mikuni was the carb of choice on this conversion, as the 42mm variant was found to be lacking when faced with the demands of the stroked motor.

There are other components that complete the package: heavy duty studs, uprated ignition module and coil, roller rocker arms, and a free breathing exhaust and air filter.

So what it like to ride?

Well the first thing that hits you is wave after wave of pure torque, a 65% increase in torque is always going to feel good. Open the throttle anywhere in the rev range and you are rewarded with a surplus of power, and this is why the conversion suits the Road King so well: a planted, stable motorcycle that carries its weight low is what's required to ensure that the most is made of the power available. Two-up, loaded with a fortnight's luggage, tickets for the Euro-Tunnel safely in pocket, there is no better bike for barrelling across Europe.

This combination of tuning parts also puts to bed the fallacy that tuned bikes are hard to live with, this FLHR is just as happy in city centre traffic as it is on the open road, no matter what the provocation, the bike refuses to get hot under the collar and behaves impeccably throughout.
The increases in horsepower is less important but still relevant. Up from 65hp to a shade over 100 is a healthy increase and is felt in all situations, and anything Japanese or Italian will be in for a shock up to around 60mph. While they are trying to get the power down in the traffic light grand prix, you will be away and changing into second.

So there you have it: a conversion that has enough power and torque to keep every type of rider happy, and which comes with the peace of mind that only a manufacturer of Harley's status can give. Cost? Well in this final specification, around £4,500 but you could get around 80% of the power for closer to £3k. The beauty of this set-up is that you can chose the components that match your riding-style and your wallet and build on them.

So what are you waiting for, the power is out there!