All of us that own Royal Stars know that they are great motorcycles. I have a '98 Boulevard that was purchased at the end of last year as a leftover and Glenn has a '96 Tour Classic. Glenn has added Vmax rear end gears as well as Vance & Hines pipes while mine remains stock. The only point in mentioning this is to demonstrate that just about any Royal Star can benefit from some variation of the modifications we are describing in this article.

We feel that the performance enhancement returned by this rather simple modification far exceeds what you might otherwise expect from a routine re-jet and filter replacement. We also feel that the concept and accompanying jet size recommendations will increase your ability to actually achieve the intended benefits with no trade off in driveability or dependability.

Basically this modification may be implemented at three different levels and they are as follows:

• Level 1 - Shimming of stock carburetor needles, mixture screw adjustment and removal of the airbox intake deflector, (no re-jetting or carburetor stack removal required).
• Level 2 - Shimming or replacement of the stock carburetor needles, mixture screw adjustment, re-jetting, (pilot and main fuel jets), removal of the airbox intake deflector and actual modification of the airbox base, (increasing the inlet to 2 inches to match the stock air filter opening). You are doing all the same work as you would do for Level 3, (Bigfoot), except you don't have to modify the air filter and the resultant jet sizes will be much smaller.
• Level 3 - Glenn refers to this as the "Bigfoot" modification as the airbox base is matched to the intake of a trimmed K&N air filter which you will see looks a whole lot like a "foot". In addition to this unique airbox modification the needle shimming and mixture screw adjustment as well as replacement of the pilot and main fuel jets, (using larger jets than Level 2), is also required.

I would also like to point out that as of this writing Glenn has completed the "Bigfoot", (Level 3), modification on his own '96 Tour Classic as well as his brother's '99 Tour Deluxe.

There are of course many worthwhile jetting kits available from other sources. Two individual air filter kits and a "Junior" kit for use with a stock airbox is available from the Baron. The "Junior" kit comes with a K&N filter and adjustable needles and this would work great as a base to grow to a "Bigfoot" at a later date, (requiring only the purchase of a few individual jets). I don't know what to say to you other than even if you only do Level 1 to "do it" .. you will be pleased. Frankly, the only additional operation required to do Level 2 or "Bigfoot" is to remove and split the carburetor stack, which you will see is not that difficult a task and to do some trimming on the airbox base.

When my Royal was newer my biggest disappointment was cracking the throttle wide open and getting a lot of noise and pounding along with an unequal amount of "go" unless I resorted to lower gears to let the engine rev. I can assure you that while the "Bigfoot" level will result in the most profound performance improvement, that any level of this modification is more than worthwhile. I don't think that anyone could anticipate just what a difference this makes. I personally feel that a modified airbox approach to increasing "airflow" is a great compromise to individual air filter kits. The modified airbox reduces intake restriction while maintaining sufficient vacuum signal in the carburetors to provide very responsive and dependable operation. When you twist the throttle at any RPM even with the "Bigfoot" the motorcycle will "move" like it never has before and much better than I think you might have ever anticipated from a modification of this type.

Well, so much for advertisement ... lets do it ... we have included a few photos to help explain the modification as we go ...

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Before beginning I purchased a Dynojet kit so that I would have "adjustable" needles, (just in case !!). Glenn purchased a Factory jet kit. In both cases we found that these needles behaved the same as stock in the 3rd needle clip position. Glenn ended up with one shim for a needle setting at 3 1/2 and so did I. On the '99 TD, two .020 inch shims, (washers were used; equal to a 4 clip needle position setting). So frankly, unless you want some extra tuning flexibility you really don't need adjustable needles. The photo shows the Dynojet's longer springs and shorter needles, (that behaved the same as Glenn's Factory needles and the stock needles despite their apparent physical differences). Glenn noticed that the '99 TD was equipped with longer slide springs, (than on the '96 TC or the '98 Boulevard), and that they are available from Yamaha - part no: 3KW-14933-00-00 if you feel you just have to have them to experiment.

This photo shows half height hex head screws installed on the slide covers and 1/4 inch polypropylene plugs installed in the pilot mixture screw holes, (which are open once the factory plugs have been removed). The hex head screws are highly recommended for the slide covers and fuel bowls. The slide covers require 12 - 4x8mm and 4 - 4x10mm screws, (although I used all 4x10mm with no interference). The fuel bowls require 16 - 4x14mm screws, (these are provided with many jet kits). All levels of this modification require access to adjust the pilot mixture screws. If you do nothing else I would highly recommend drilling and removing the brass factory plugs, (if equipped), removing and coating the mixture screws with Never-Seize or a silicone grease. This action will provide adjust ability in the future as these screws will easily corrode to the carburetor body and once damaged may render the carburetor unserviceable.

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OK .. lets really get started. Remove the seat and the chrome console cover on the top of the gas tank, (three screws and lift if off). Next, be sure to disconnect the green speedometer connector located in the wiring bundle behind the gas tank, (be sure it is clear of the tie wrap .. which if you haven't noticed yet is easily released with a tab and is reusable .. as are most on the whole bike). Also remove the two bolts securing the rear of the gas tank, (top center of the photo).

Remove the rubber covers, (they just pull off), and the bolts on both sides securing the front of the gas tank. With the console cover now removed, disconnect both electrical connectors, (the large one has a "push button" to release it). Don't forget to disconnect the gas tank vent hose, (this operation is omitted in the service manual but you won't be going anywhere with the tank if you leave this connected).

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Be sure to turn the fuel tank petcock to "off" and disconnect the fuel line. Now you are ready to lift the gas tank off the bike. I usually throw a towel over the tank when I do this to prevent any belt buckle scratches or other horrors. No matter how good a modification you are doing ... nothing takes the edge off of the enjoyment more than causing unintentional damage. Covering the side of the engine you are working on also helps prevent those pesky little nicks that appear on the tops of the case covers or mufflers as a result of dropping tools or fasteners. The right photo shows the bike with the tank successfully removed and stored out of harms way.

A single bolt will release the wiring guide attached to the frame and allow easy movement of the wiring harness that is blocking your view of the screws at the base of the airbox spigots on the left hand side of the bike. On the right, two plastic retainers are easily released with a screwdriver which will free the coolant line and allow access to the airbox screws on that side. The right photo shows the bike with the airbox removed. As it is removed the crankcase vent hose at the rear is easily detached. There is also a small diameter drain hose on the underside of airbox forward of the left front carburetor. It will simply pop off and can be reattached from underneath when the airbox is reinstalled.

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The left photo shows the coolant line released for access on the right side of the bike and hanging down in front of the right bank of carburetors. The right photo shows the airbox removed and the nose deflector detached. If you are doing a Level 1 modification this is all you have to do to the airbox, (remove the deflector and leave it off).

At this time if you are only doing Level 1, (shimming the needles and adjusting the mixture screws), then the coolant line on the right and the wiring harness on the left of the carburetor stack can easily be manipulated to allow access to the slide covers which will allow the carburetor diaphragms, (slides) to be removed. The .020 inch thick washers needed to shim the needles may be obtained locally or even from Dynojet online at http://dynojet.com.They will provide you with an assortment of needle c-clips and washers for about $9 USD, (many more than you will ever need). These are also provided in most jet kits. If you wish to obtain these at a hardware store or Radio Shack etc .. the actual measurements of a Dynojet washer is .020 inches thick, with a .231 inch overall diameter and a .127 inch center hole. The washer has to slide on to a stock needle which is .100 inches in diameter. The needle assembly within the slide is fairly obvious, (see the photo at the beginning of this article). The shim/shims are used to raise the needle and are placed between the c-clip and the needle collar. If you haven't done this before you will note that there is a small tip on the needle collar that sits into a small hole visible in the end of the slide. Make sure you rotate the needle assemblies when you re-install them so that this tip seats properly in the nose of the slide.

Also, if you haven't noticed ... these carburetors are exactly the same as those used on the 650 V-Star, (sans chrome slide covers some attachment hardware and the fact that we have a cluster of four instead of two). Mark Jelic completed a "GAK" article for the 650 in an earlier issue of the "StarCruiser" and it is worth a look if you are doing this modification; he has some great close-up photos of the needle and slide assembly. It can be viewed at - http://www.star-riders.org/starcruiser/volume1-1/gak.html

Your mixture screw holes may be covered with a "factory" plug. These are easily drilled out with a 5/32 drill. Go lightly .. the drill will usually start to break through and grab the plug; care must be taken not to go overboard and damage the slotted heads of the mixture screws underneath the plugs. Be sure to use a vacuum or a blow gun to clean out any debris remaining in the mixture screw holes.

When adjusting the mixture screws be sure to use a screwdriver with the best fit possible. Do not force these screws excessively as they are very delicate and if broken may render your carburetor unserviceable. Marking your screwdriver with a line, (use touch-up paint), at the base of the handle will make it a lot easier to count "turns" when adjusting these screws. The first thing you should do is to turn the screws in clockwise until seated and record the number of turns, (these are your factory settings). Then remove the screws completely and coat the threads with a Never-Sieze compound or silicone grease. For Level 1 re-seat the screws and then turn them back out to the original factory settings plus 1/4 to 1/2 turn. This will slightly richen your pilot mixture with some relative equality in relation to the original factory adjustment.

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These photos show the airbox removed and the top and bottom separated providing a better view of the restrictive 1 3/4 inch entry tube that extends into the base of the airbox .......

To remove the carburetor stack the throttle position sensor must be disconnected. Although it is not necessary I also remove the choke cable guide that spans the rear two carburetors. This allows additional clearance and makes it easier to detach the throttle cable assembly as well as the fuel line. Loosening the manifold clamps will then allow the carburetor stack to be popped off and slid out the left side, (pull up firmly at each corner until the stack is free). The two fuel bowl vent hoses are easily disconnected from their fittings once the stack is free. This is a great opportunity to do some house cleaning in the engine valley and to access the valve cover "covers". Be sure to plug or cover the manifold holes to keep "things" from accidentally finding their way into your engine. I also took the opportunity during my first removal to re-position the fuel bowl vent fittings located below the carburetors so that these hoses could be re-routed on the inside of the two front carbs for a cleaner appearance. A light coat of silicone grease on the inside of the manifold openings will allow the stack to "pop" right back in place with minimal effort during re-installation.

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The left photo shows the bottom of the removed stack. The carburetor pairs, (left and right), must be separated to allow access to the fuel bowls. This requires that the choke cable be removed as well as the throttle connecting link between the two halfs. The throttle link only needs to be released on one side and is retained with a small washer and a very small cotter pin. The right photo shows the two halfs being split apart. The screws on the side and top brackets only need to be removed on one side. The fuel bowl drain hose can simply be slid out of its' retainer and the clamps holding the rubber hose connection between the two fuel bowls should be slid to the center to allow separation.

These photos show one half of the stack turned upside down to allow easy access to the fuel bowls. Replacement of the fuel bowl screws with 4x14mm hex head fasteners is highly recommended. Take care when removing the existing screws. A few taps or the use of an impact driver may make their removal less frustrating. My fuel bowl screws came out quite easily but this generally is not the case so it is nice to have hex head replacements on hand which will also allow un-eventful access in the future.

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These photos show a better view of the jets in the fuel bowl. The large slotted jet in the center is the main fuel jet and the small one to the right is the pilot fuel jet. Actual size recommendations are discussed at the end of the article. Also shown is the base of the stock air filter. The opening at the end is 2 inches in diameter.

The left photo shows the trim pattern laid over the airbox base to complete the "Bigfoot" cut, (on this box the original opening has already been matched to the 2" filter opening). The right photo shows the actual cut pattern transferred to the non-foam side of an air filter, (for better visibility). Unlike the stocker, the K&N filter has a suitable foam sealing surface to accommodate the "Bigfoot" cut.

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Jetting Recommendations and Qualifications

If you are doing a "Level 1" you obviously do not require any jets; only the shims/washers.

For Level 2, the "two inch" filter hole match then you should be starting in the vicinity of a Mikuni 105 -110 main fuel jet and a Mikuni 22.5 pilot fuel jet. Stock jetting uses a Mikuni 95 main and most have a Mikuni 20 pilot fuel jet, (the '99 TD had a 17.5 pilot fuel jet installed along with the longer slide springs however and this is normal for this model).

For "Bigfoot" you will need a Mikuni 117.5 main fuel jet and a Mikuni 22.5 pilot fuel jet. Glenn has toyed between 3 1/2 and 4 needle clip positions to try to find the very best on his '96 TC and the '99 TD ended up with 2 - needle washers, (equiv. to a needle clip position of 4). On both of these bikes they were rewarded with an outstanding performance improvement and "finally" a nice light tan spark plug reading.

Glenn experimented with several variations of this cut. In one case, the original front tube was trimmed flush with the base of the airbox but was left at 1 3/4 inches; a single 2 1/4 inch round hole was added in the rear. This setup worked best with Mikuni 115 mains and Mikuni 22.5 pilot fuel jets.

Glenn lives in Georgia at an elevation of approximately 800 feet, I am in Arizona at 1150 feet. These jetting recommendations seem to be proper for both of these locations. Obviously, if you were at sea level you might be able to benefit from a 120 main jet or at more extreme, (higher), elevations you might be better suited to a 115 or I suppose if you live in Denver you might even get by with a 112.5 or less ... If you decide to try a different airbox base configuration then simply make jetting adjustments as required. The values suggested in this article and their associated airbox "cuts" should help you make an intelligent selection no matter what you do.

For the pilot jet I think you will find the 25 right on the money for more moderate elevations and a 22.5 for the high altitude folks. (Subsequent testing has found the 22.5 to work pretty well all round.)

The main fuel jets used in this carburetor are Mikuni N102.221 and are referred to as the "Small Round or Super BN" type. The "larger" version, Mikuni N100.604, ("Large Round" type), are also usable since the jet is open in the fuel bowl and head size is not a factor. The pilot fuel jets are Mikuni VM28/486. These jets are available from a number of sources including Sudco, Dennis Kirk, (for large head mains), and even Yamaha, (see the Yamaha and Dennis Kirk part number cross-reference immediately below).

Glenn used Harper Discount Yamaha in Hendersonville, North Carolina - 828 692-1124 - who was able to supply the jets promptly and at a very reasonable price. You might try them and save yourself some of the pain I endured. They should also have the K&N filter.

The K&N filter part number for the Royal Star airbox - YA-1595

Setting the Pilot Mixture Screws

When you install the larger pilot fuel jets you will normally not need as much mixture screw as you have been using. I realize that you can have your mixture screws set on an EGA device at 3.5% and live happily ever after; if you have easy access to such a service then I would highly recommend it. There are other devices on the market such as "ColorTune" that make this task equally precise. However, I think you can do a sufficient job of adjusting these using the "RPM drop" method. This consists of adjusting the screw out for the highest RPM. I normally turn the screw in, (do one cylinder at a time), until it is seated. You should notice a significant change in the idle quality. I then turn the screw out until the engine smoothes out and add 1/4 to 1/2 turn to this adjustment. I verify that the setting is reasonable by checking the plugs, looking for sooting and poor hot starting performance, (if you have set these too rich the bike will have a hard time starting when hot, you will also get excessive sooting when idling for an extended period of time).

Even though you might have set these slightly richer than necessary in the past when you had the stock pilot fuel jet in place ... possibly to deter backfires and/or to enhance low end performance this will not be necessary with the larger pilot jets installed. The real purpose of the pilot mixture screw, (also referred to as the "idle" mixture screw), is to meter "whatever" pilot mixture you happen to have in order to support the engine at idle. It certainly continues to contribute mixture well into the RPM range but there is no purpose to adjust for any function other than idle. This will keep your engine running nice and clean and the recommended pilot fuel jets that you have installed will absolutely "knock you socks off" as soon as you move that throttle off-idle. Trust me ... you are really going to like this modification.

Summary

I really don't know what else to say other than "do it". To say you will be pleased is indeed an understatement and I am sure you will agree once you have completed the modification. Cutting the airbox or the filter is not difficult and there are several ways to accomplish this task. The actual mechanical work may seem to some to be a little "much". You can always team up with another who is more mechanically inclined or possibly has more suitable facilities than your apartment living room. Don't forget to synchronize the carburetors whenever they are split for rejetting; this is an absolute necessity. Consider all of the operations involved carefully and make sure you have the tools to complete them in a competent manner.

Whenever there is a possibility for you to successfully complete a modification such as this or even do your own maintenance I feel it can only enhance the enjoyment of your motorcycle. If you attempt this modification or have questions, Glenn, myself and many others can always be found in the Royal Star folder on the ISRA Forum and will be glad to help.

I want to say a special thanks to Glenn. I may have compiled the article for us and added a few photos but its' completion would not have been possible without all the timely testing and encouragement he provided, (ie ... to "quit fooling around and make the BIG hole").