Mike's Magna Mods

My ultimate goal is to make the Magna as reliable, fun and comfortable to ride as possible. This means obtaining the maximum performance possible with bolt-on mods and no engine or machining work.

Overall, my mods are:

Gearing: 7% shorter than stock (15 / 40)
Carbs: jetted for optimum performance
Air box: K&N filter and sealed air box
Exhaust: Vance & Hines classics II 4-in-4 glasspacks
Ignition: Dyna 3000 on advance curve #4, limit 11,000 RPM
Brakes: stainless steel braided front brake hose
Front suspension: Progressive springs with 15W oil
Rear suspension: Progressive 412s with heavy duty springs
Wind protection: NYC flyscreen
Horn: dual Fiamm electric air horns

Details:

The first mod I made to the Magna was to install dual air horns. One of the Wolo horns I originally installed died, so I replaced it with a Fiamm. I liked the Fiamm so much I went out and bought a new pair of Fiamms. They are rated at 110 dB at 10' distance.
End Result: Improved safety

The next mod was to install a flyscreen windshield. It's small; just big enough to deflect the wind out of my gut on the freeway. It's a high quality piece with smoked glass and chrome mounting hardware.
End Result: easier bike control on windy days and freeway riding

The next mod was to change the gearing. Stock Magna gearing puts redline in 2nd gear about 80 MPH, and 5,000 RPM at 75 MPH in top gear. I replaced the stock 16 tooth front sprocket with a 15, which is about 7% shorter. Now it pulls about 5,300 RPM where it used to pull 5,000 RPM. This improved acceleration off the line and top gear rollon. I tried 15/43 for a while, which was great for putting around the island but it was just too much gear for the freeway.
End Result: Stronger acceleration

The next mod was to adjust the carb mixture. My Magna was poorly adjusted by the dealer, inconsistent and nowhere near specification. I adjusted it to the 49-state setting and it runs smoother and starts better.
End Result: improved throttle response & starting, improved fuel economy, extended engine life

The next mod was to adjust the carbs for maximum performance. I installed the Dave Dodge kit, which involves adding one extra shim on each main jet needle (for a total 2 shims each) and changing the main jets from size 102 to size 105. I also installed a K&N air filter and adjusted the pilot mixture to 3 turns open.
End Result: more power and torque, smoother, fatter torque curve, better engine sound, extended engine life

The next mod I made, during the carb adjustment, was to seal the air box. The Magna tends to leak oil from the airbox where it mounts to the top of the carbs. I sealed the join with hi temperature silicon seal.
Here are some pictures: overview and close-up. The orange "goo" is the sealant I used. Observe the absence of oil leakage!
End Result: no oil leaks, better seal, lower Si in UOA

The next mod was to install a Vance and Hines. high performance exhaust system. Combined with the carb mods, this boosts midrange torque and top end power. However, after installing the exhaust, the dreaded midrange flat spot returned. The Dave Dodge jet kit just wasn't enough for this high flowing exhaust.
End Result: power, torque and efficiency, better engine sound

The next mod was to install a stainless steel braided front brake hose. Bleeding the brake afterwards can be a real PITA. Best way to do it is to hook up a reservior of fresh brake fluid to the lower bleeder bolt, loosen the bolt and feed the fluid up into the system (from bottom to top) until it fills the master cylinder. Then bleed the system as normal. here is a small, cheap, good quality hand crank fluid pump that does the job nicely. It's designed for fueling R/C model airplanes but works perfectly in this application.
End Result: better control & power from the front brake

The next mod was to install a Dyna 3k ignition. This unit provides 10 different timing advance curves, each optimized for a different bike setup. For my configuration, curve #4 is best. This keeps the midrange the same, while providing more advance at the low end and high end. I also set the rev limit to 11,000 RPM.
End Result: more low end torque & more top end power

After this I noticed the bike seemed to run a bit lean despite the rejetting. Turns out the V&H flow higher than the aftermarket exhaust that the jet kit was designed for. Add the K&N air filter and it flows even more, and the Dyna made it more sensitive. I replaced the main jets with size 107.5 to correct this. Now they're 2 sizes over stock (102 --> 105 --> 107.5). I kept the same 2 shims on each needle and set the pilots at 3 turns. During this process I eliminated the PAIR (pulse air injection) system. This quieted the exhaust somewhat and removed several hoses and parts from around the carbs.
End Result: smoother torque curve, more power and less noise

Finally, in October 2008 I rejetted again (the 3rd time). I got tired of the midrange flat spot caused by the Dave Dodge jet kit not being rich enough for the V&H and K&N combo. The bigger 107.5 mains helped a bit, but there was still a midrange flat spot at more than 1/2 throttle. I added one extra shim to each needle - total of 3, or 2 more than stock. And I lowered the pilots from 3 turns to 2 3/4 turns. Now my carb settings are:

  • Size 107.5 main jet - two sizes bigger than stock
  • 3 shims on each needle - two more than stock
  • Size 40 pilots - same as stock
  • Pilots at 2 3/4 turns - 1/4 to 1/2 turn more than stock

    • End Result: This configuration is great. It has the fattest, smoothest, best throttle response I have ever had in any motorcycle I have owned. It doesn't have the raw power of my old Katana 750 or modern sport bikes, but it has great throttle response. It's got surprisingly fat low end torque for a 750cc 4 cylinder that gradually builds through the midrange to an impressive top end surge of power. It is better than most computer controlled fuel injected cars I have owned. This is the throttle response that all motorcycles should have!

    Jetting Overview

    The Magna is jetted differently from the factory for US and non-US markets. US Magnas run leaner in order to make the EPA happy. CA Magnas are jetted the same as 49-state models, but have extra emissions controls.
    The US jetting is:
    Size 102 main jet, 1 shim on each needle, size 40 slow jet, pilot screw set at 2 turns.
    The non-US jetting is:
    Size 105 main jet, 2 shims on each needle, size 40 slow jet, pilot screw set at 2 turns.

    The US Magnas have a midrange flat spot in throttle response due to the smaller main jet and 1 less needle shim.
    Stage 1
    Stage 1 is to restore the non-US jetting. This eliminates the midrange flat spot, boosts low end torque and improves overall throttle response. It works best with the factory exhaust system and air filter. It also works well with most of the aftermarket slip-on exhausts. They don't improve flow enough to make a significant difference in jetting.

    Stage 2
    Stage 2 is to tune the jetting to match the bike's configuration. For example, the K&N air filter is not alone enough to need a jetting change, but when combined with an aftermarket exhaust it can be. The V&H exhaust alone increases flow enough to require more than Stage 1 jetting.