Harley-Davidson stage 1 bikes are pretty easy to spot. For a start the air filter is the most visible part of the upgrade because it isn’t sunk into the plastic moulding in between the motor and air filter cover.
Harley-Davidson Stage 1 Horsepower Increase
In stage 1 there is no internal mechanical modification required all we are looking to do is to make the means of getting the fuel in and exhaust gases out more efficiently. There are more things you could do though such as including ignition modifications if this is within your budget. You can go as far as you want, but the most common basis for a Stage One is a Screamin’ Eagle High Flow Air Cleaner kit and a pair of slip-on mufflers.
You have to remember that the build of your bike when it comes out of the factory is within regulations and if you start messing with those specs you have to accept the responsibility that comes with flouting the regs.
If you are looking through parts catalogues you’ll start to notice the crossed chequered flags marked as “For Race Applications Only” and you will see these more and more often as you continue to stage your Harley.
Normally fitting an air filter is straightforward but when looking at a stage 1 upgrade you will quickly realise that one of the bits of emission control are the mounting studs holding the air filter backplate on – these are actually engine breathers from the cylinder head, hence why it is called a “kit” rather than a simple air filter.
The purpose of the kit changes the flow route and then it’s a matter of fitting the supplied filter onto cast mounting plate (which will have been adjusted) therefore allowing for greater airflow. It is just a case of then refitting the stock cover or supplied alternative.
Having let the air flow more freely, it’s essential to consider the impact on the calibration of your EFI or the jetting of your carburettor. More air means proportionally less fuel, and that means a lean mixture: sort it before you run it in anger, or it could overheat and potentially seize.
Assuming that the mounting bolts are still in good condition the Slip-on mufflers are easy enough on a new motor.
These Slip-on mufflers provide less restriction for the exhaust gases and are louder as a consequence which is why a lot of people buy them just to make the bike LOUDER – which is enough for some people and is their whole reason for the stage 1 process. But you really don’t have to stop at this point.
Having got the air into the carb more quickly, and eased the path of the exhaust gases, it makes sense to make sure the fuel metering system is working as efficiently as possible so you want to have a look at that – and there’s more to fuel systems than jetting and the recalibration of stock EFI modules.
This is where things can become contentious. There are many ways in which you can sort out the original CV carb from a Dyno Jet kit to throwing it away and replacing it with a slide carb, and your decision will largely depend upon who you speak to but your decision will likely be based upon how much experience you have of tweaking carburettors, how much you’ve got to spend and whose advice you most trust. As regards to EFI, the stock unit can be recalibrated to account for the changes, on a dealer’s rig, but Harley themselves don’t offer alternative units beyond that calibration, and your warranty will suffer if you play away.
Harley supply different jets for their Keihin carb and, if you know what you’re doing and have access to a Dyno to speed things along, then this is definitely is as good a starting point as anywhere. The factory-supported DynoJet recalibration kit is a common alternative to take a lot of the guesswork out and can be backed up by their Thunderslide, which is a redesigned lightweight replacement emulsion tube and slide needle for the CV and offers improved throttle response. Another alternative, but by no means the last one, is the Yost Power Tube: a selection of jets and the Power Tube itself, it’s designed to eliminate flat spots and otherwise get the best out of your carburation.
Screamin Eagle / Mikuni Carburetor
You could get yourself a Mikuni HSR-42, or a Screamin’ Eagle 44mm CV – FYI Screamin’ Eagle sell a 42mm slide carb which is made by Mikuni -both carbs are for, let’s be frank, competition use, but if you’re going to stick the big bore CV on you then have to think about a a 44mm manifold to bolt it onto. A street-legal 44mm CV is also available for 2001-on Twin Cams and possibly points the way to future legislation.
Talking injection now, you’re pretty much stuck with the factory fittings and of course you could grab yourself an aftermarket part but be prepared for a bit of a battle if you have to claim on the warranty because there are a number of mechanical things that the fuel mix can affect.
Exhausts are just as intricite. Slip-on mufflers are by far the easiest, but a full system will deliver more in terms of a decent upgrade but that is a whole new discussion on it’s own. One thing is for certain is that the balance pipes will remain in place if you just fit mufflers, while aftermarket systems will often lose them.
Balance pipes break up the lines of the V-twin on Sportsters and FXRs but are generally there to reduce noise, reducing the speed of the exhaust gas by allowing it to dissipate before it exits the muffler, but there are many people who blame them for poor performance. The “hidden” low-level balance pipes on Dynas and the new Sportster mean they will stay in place for longer, as they don’t detract from the appearance, but there are increasing numbers of people who are leaning towards 2-into-1 systems like Vance and Hines, Supertrapps or Thunderheaders, and they don’t come much more balanced than both pots exiting the same silencer.
And that’s the main stuff, but not everything because there are a few other things you can do without taking a spanner to the cases, and they are the bits that light the fuel – and a good thing to do if you’ve gone to the trouble of fixing the carb.
As you’d expect, Screamin’ Eagle offer a range of ignition systems, both street legal and “competition” which better match the spark to the less restricted motor, while Crane’s Hi-4 and Dyna’s Dyna2000 remain popular choices for those less concerned by their warranties, and have an element of tunability built in so you can experiment. And if you’re going to play with ignition modules, why not coils? And why not plug leads?
All of which falls within the remit of a Stage One.
There’s nothing in there that a reasonably competent home mechanic can’t tackle, but if your bike is still within its warranty period, you’d be best advised to talk to your dealer and make sure they’re not going to suck hard through their teeth when you bring it back, having made a mess.
What sort of mess can you make?
Too weak a fuel mix if you’re playing with the carb, injection module or air filter, so keep an eye on your spark plugs afterwards and make sure they’re the right colour. Getting an air-leak in the system if you mess about with the carb or manifold, which will make it pop under load and on the overrun, and ultimately could blow the rear pot. Getting the ignition timing wrong if you’ve got a fully adjustable unit that will let you play beyond your expertise, in which case it will run badly. Shearing or stripping something by overtightening it, so get a torque wrench or be cautious … no, get a torque wrench: it’s potentially more dangerous for something that hasn’t been tightened up enough to fall off than it is to shear it. Rounding off a perfectly good nut or bolt by using the metric spanners from a previous bike, or your dad’s old imperial spanners, so get decent tools before you start.
Simple stuff really, but be aware that your dealer would rather do the job for you and charge you for the privilege – but also that you’ve got some comeback if they mess up. Also be aware that the fitting of anything non-Harley to your warrantied bike might cause a raised eyebrow, and that even Screamin’ Eagle kit is no guarantee of your warranty surviving intact.
While mentioning that Stage Ones don’t need to have a spanner laid on the engine, it doesn’t actually mean that a Stage One can’t have a Technical: Harley-Davidson Staging spanner laid on its engine, and a Stage One 1550 is actually quite possible. Rebore the original barrels, and drop a pair of the 1550 pistons in under the stock heads and hey-presto! You’ve got a Stage One 1550cc. You can leave the cams alone, although you wouldn’t get the full benefit until you did look at the cams and that would be…
To see an overview of Harley-Davidson staging please click here otherwise click here to see our Harley-Davidson stage 2 article
With thanks to Andy Hornsby of American-V magazine from which parts of this article have reproduced . Originally published 22/1/2004 © American-V magazine