ATV Sport Performance Project
Duncan Racing Holeshot Banshee
by ATV News Staff
OUR YAMAHA BANSHEE WAS UNDERGOING A SERIOUS IDENTITY CRISIS. It had been through a number of aftermarket parts, some it liked, some it didn't. It also has a complete makeover recently, and it was feeling better because of it. But what it needed most were engine mods that worked, and it needed them fast. Or is that, it needed to go fast? Yeah, that last one. That's it.
We didn't want to do just another Banshee modification article. And besides, our Yamaha has some special needs. You see, it's ported, big time.
Its first project was performed by quad-performance newbie Rossier Engineering of Wisconsin. Rossier's ace two-stroke specialists (years building super fast Sea-Doo race boats) took our Banshee for a while and turned the cylinder into Swiss cheese. Don't get me wrong, that was fine because they also made it super fast (see February 1999 issue).
We chose unfinished pipes, though most people prefer the chrome version.
It gets difficult trying to match someone's porting to someone else's pipes, carbs, and intake specs. We took all the performance parts off of that Rossier-modified Banshee and returned them. It was a fun ride, but far too much top end for the small motocross tracks we ride most often. We needed big low-end power. We wanted a Banshee that ripped off the starting line and out of corners.
We called Duncan Racing's Loren Duncan, builder of the motocross Banshees ridden by Open-class champ Travis Spader. We knew Duncan could tell us what we needed. And if we sounded kinda sorry and pathetic (not hard to do), he'd even build the parts in a hurry and rush them off to us.
Performance Parts Team
Duncan wasn't so quick to simply send us parts. He had understandable concern about the cylinder work that had been done. He wasn't familiar with Rossier's work, and normally liked to look at the cylinders and verify the porting specs. We didn't have time to mail the cylinder to California, so we got the porting specs from Rossier and passed them on to Duncan. With this info, he was ready to prescribe the right medicine for our ride needs. All we had to work with was a pair of ported Banshee cylinders, and a slightly modified airbox. The stock head was milled to raise compression, though we still ran high-octane pump gas.
Duncan recommended Paul Turner midrange pipes with Duncan Fat Boy silencers. On the intake side, he said we could use the stock airbox, but would need a new K&N filter, and a Pro Design intake flange. From there, the air would mix with the fuel in Keihin PJ34mm carburetors. It would enter the cylinders through the unique Pyramid reed valves and reeds, with the added benefit of a Master Flow intake manifold system.
We also added a Motion Pro twist throttle (easily the most controversial product installed on this machine among our test riders), and new Tag Metal handlebars. Graphics and seat work was provided by One Industries.
Finally, and a very important addition to this recreational MXer, are the ITP Holeshot tires and aluminum wheels. We went with the 18-inch rear Holeshots, a must size for any MX track riding
I know what you're thinking. How can we turn this Banshee into an MX machine and still run the stock chassis and suspension? Well, we can't really, but we can only do so much in one project. You have to give us room for further modifications.
The Masterflow intake manifold and pyramid reed valves really boost throttle response.
Read, Then Wrench
The next best thing to having Loren Duncan personally build your engine (we didn't) is to have him write your instruction guide (we did). Of course, we didn't read the instructions right away, and were suitably embarrassed when we called Duncan wondering why our Banshee wouldn't idle correctly. He asked is we'd followed the instructions exactly. We said, No. And we went right back to the toolbox and the installation project.
The installation is actually very easy, you simply need to make sure that you follow the provided guidelines for carburetor setup. Once we had the proper jets installed, and had set the mix and idle screws to precisely the right spot, we got closer to a tuned Banshee.
One very important aspect of Banshee tuning, and the key to getting ours to idle properly, is in synchronizing those twin carburetors. The Keihins connected to the Motion Pro twist throttle made this a little easier than stock. It's also easiest to do this with the airbox removed, but it can be done with the box in place. If the carbs aren't opening and closing exactly in synch, the engine won't run correctly. If you're really good, you can hear the carbs open and close together (with the engine off, of course).
To get the aftermarket carburetors to fit in the chassis, you'll need to slightly bend the clutch cable connection to the case. You need the extra clearance for the Keihin's deeper float bowl.
The only other modification you need to do for this installation is at the airbox. The rubber ducts that connect the box to the new carbs need to be cut down in length to fit. Nothing that a sharp knife or good set of clippers can't handle.
Every other aspect of this installation was simple, and clearly laid out in Duncan's instructions. The pipes and mufflers fit perfectly, and that doesn't always happen with aftermarket components. All the mounting hardware and brackets matched like they came from the factory. The boost bottle and the reeds were also easy to install, even twice since I mounted them incorrectly before reading the instructions.
No chassis or suspension mods, yet, but we did feel the need to get rid of the stock tires and wheels. It's not that the stockers are that bad, they're just not durable or solid enough to stand up to MX track riding. And there is so much better equipment available from the aftermarket.
We chose ITP's smallest Holeshot tires on the ITP aluminum wheels. We went with the 18-inch rear tires and the 19-inch fronts. And what a difference rubber can make. We could have changed sprocket sizes to make the most of our engine power and tire choices, but we didn't. We found the machine to have plenty of MX riding oomph. And we can easily change back to the stock tires for woods riding, without have to worry about sprocket sizes.
The other improvements we made to this Banshee we highlighted in our last issue. The quad was looking tired, so we stripped it clean of its old stickers and graphics. We shined up the plastic with Plastic Renew, and we installed a new graphics kit and seat cover from One Industries. The stickers and seat cover are holding up very well to all of our riding time abuse.
The Banshee's exterior was assisted by One Industries and Tag Metals.
The Real Test
While we can tell you how much we enjoy these mods (and we will), and how our Banshee really burns up an MX track (and it does), we'll let the numbers speak for themselves first.
We used our Stalker Acceleration Testing System radar gun and software to measure the machine's newfound power. Compared to the stock Banshee (though this Banshee hasn't been stock for several months), this Duncan-prepped ride is a rocket.
Check out these numbers (gleaned from our new Stalker radar gun and software system).In stock form a Banshee still feels very quick
