12. What modifications can I do to make my bike run better/faster/stronger? return to Master Table of Contents
12.1. There are several performance modifications that range from changing the air intakes, to re-jetting the carburetor, to replacing the stock exhaust pipes with straighter, high performance (i.e., fewer baffles and packing in the pipes) exhaust systems.
Here's a page of COMBINED MODS for a set of 39 bikes that have been rejetted after BOTH the air intakes were changed, and after market pipes added. This will give you an idea of the range of after-market pipes available, too.
12.2. No longer sold is the Dyna2000 (D2K), a third party IC Igniter or ignition system from DYNATEK http://www.dynaonline.com/, for BUBF's was designed for higher performance and increased mileage. There have been reports of significant performance improvements and increased gas mileage with some users not having any improvements. You are cautioned to do further research in the VROC archives and post messages to the VROC newsgroup for the latest news, status, and availability of a used D2K. The original LIST PRICE was approximately $325.00 plus shipping and handling. Several are currently installed in BUBF's. The author is not aware of where a new Dyna2000 can be purchased.
12.3. We must warn you that these and any other modifications can and in many cases could increase/decrease performance at the cost of fewer miles per gallon. You should do thorough research and discuss the matter with your mechanic who will make or help you make these modifications. But please keep in mind the following: the STOCK 1500A/B/C’s produce a lot of power and speed as they come off the dealer’s floor or purchased from someone who has diligently maintained their 1500 BUBF.
12.4. You also need to be aware that if you dramatically INCREASE the engine’s air intake, you will need to adjust the air/fuel mixture by installing larger fuel jets in BOTH carburetors.
18. How do your Keihin carburetors operate? return to Master Table of Contents
18.1. Your BUBF Keihin carburetors are meant to mix fuel and air and meter it to the engine. The concept is simple, but the process is quite involved. This is at best a high level description.
18.2. Your engine starts "breathing," or sucking in air when you first press the starter switch. The switch activates two relays which allow electrical current to flow to the starter motor. The starter motor turns the engine crankshaft. This moves the pistons, beginning their traditional 4-stroke cycle: intake, compression, power and exhaust strokes. During the intake stroke, the piston moves downward from top dead center creating a vacuum in the cylinder. The vacuum is "filled" by the air-fuel mixture produced by the carburetor mixing fuel from the carburetor bowl and air from the air intake system.
18.3 The pilot jet meters fuel to the carburetor at idle (and low speeds). At idle, fuel is fed to the carburetor through the pilot jet, only. The amount of fuel flowing to the idle mixture can be adjusted by a pilot screw on the side of each carb. The idle speed (rpms) is controlled by the idle knob on the left side of the engine roughly between the two carburetors.
18.4. When you twist the throttle, you are simultaneously opening a butterfly valve on the engine side of each carburetor. This begins the mid-range carburetion process as the clean filtered air from the air intakes is pulled through the carburetor's Venturi chamber and mixed with fuel. The Venturi chamber makes up the single largest portion of the carburetor body. Visualize the Venturi chamber as two funnels connected together at the smallest ends and laid on their side horizontally. One end accepts air from the air intake system and the other end provides an air-fuel mixture to the cylinder. Air enters the Venturi. The air is slightly compressed as it moves towards the narrow Venturi center, and pressure increases relative to normal ambient pressure around/outside the carb. As the clean air passes into the widening second section of the Venturi chamber, the air travels faster. The pressure in the engine side of the Venturi is reduced causing the fuel in the carb bowl which is under normal atmospheric pressure, to be "pushed" up or sucked into the Venturi chamber through the jets, atomized, and mixed with the filtered air. The increased fuel and air are combined and a larger volume of air-fuel mixture is drawn into the engine cylinder creating a stronger explosion in the cylinder forcing the piston downward faster, and increasing RPM’s.
18.5 .The jet needle/slide combination control fuel flow and Venturi opening size at medium speeds, and the fuel flow through the main jet at higher speeds. As you continue to roll the throttle and open the butterfly valves further, more air can move through the Venturi faster, decreasing the pressure difference between the Venturi and a chamber below the needle/slide diaphragm causing the diaphragm connected to the top of the needle/slide to push up lifting both. As the jet needle moves upward, it’s withdrawn from the needle jet and main jet, allowing more fuel to pass into the Venturi. More air is also allowed to pass through the Venturi when the needle/slide moves upward out of the Venturi throat. This keeps the balance of air to fuel volumes close to the optimum 14:1 ratio.
return to Master Table of Contents18.6 As your rpm’s increase, the overall effect of the pilot jet is lessened and the main jet provides an increasing percentage of fuel to the carburetor that is mixed with the increasing amount of filtered air from the bike’s air intake system.
18.7 Please remember that the pilot jet is not "turned off," but continues to flow fuel to the carburetor, even at higher rpm’s, but it’s relative effect as a total percentage of fuel to the carburetor is lessened as the main jet flows more fuel as the needle is withdrawn from the larger needle jet./main jet. At full throttle opening, the needle has cleared most of the main jet. Given a #42 pilot jet and a #112 main jet (.42 mm and 1.12 mm respectively), the pilot jet is supplying less than 15% of the total fuel to the air fuel mix.
18.8 As you roll back the throttle to "slow down," the butterfly valve closes and less air-fuel mix reaches the cylinder. Rpm’s begin to decrease. Air pressure increases in the chamber above the carburetor diaphragm and the needle and slide move downward to decrease the flow of fuel from the main jet with the slide decreasing the flow of air. As the needle seats itself in the main jet and the slide reaches it’s lowest point, the pilot jet is again the only source of fuel to the carburetor. During deceleration, the coasting enricher located on the side of each carburetor, decreases the flow of air to the idle circuit, enriching the air-fuel mixture going to the cylinders to reduce backfiring. The coasting enricher is made up of a diaphragm that is activated by the pressure change in the carburetor during deceleration. The diaphragm infrequently becomes damaged or worn over time. The coasting enricher can be easily disassembled for inspection using your service manual as a guide.
TECH TIP: I had a chance to take apart the coasting enrichers (c.e.’s) on both BUBF carbs last night. They’re easy to get to without taking the carbs off the bike. The cover on each c.e. is held in place by two screws. BE CAREFUL, there’s a spring under the cover that can surprise you. There’s also a small (1/8" diameter) rubber gasket that fits under a tab on the cover that can slip out. If it falls out, put it back in place with the FLAT side of the gasket towards the carb. You might want to put a clean rag under the carb to catch screws and gaskets that get away from you.
Under the cover, there’s a concave rubber diaphragm attached to a brass plunger that fits into the c.e. body. The diaphragm has an edge that fits in a groove in the c.e. metal body. It’s a much smaller version of the slide diaphragm and appears to serve a similar purpose: to raise the plunger to meter air to the carb idle circuit at deceleration.
I found that the gasket on the front carb that has been giving me farts and blams had two small "white" spots on the inside. On closer inspection with a bright light behind the diaphragm and stretching the rubber material, the two spots turned out to be two small rips about the size of a pin hole. For a temporary fix to check out the c.e., I put a dab of rubber cement on the cover side of both holes, and put the c.e.’s back together. The other diaphragm had no holes in it.
I warmed up the engine (it was 10:00 PM and too cold to ride). I blipped the engine throttle and what were farts and blams out the front cylinder tail pipe turned into one or two small pops. I need to get in a ride to test this out as well as install the Colortune again, but so far, the pinhole rips in the front carb c.e. gasket might to be causing deceleration problems.
There is at least one one air circuit in the c.e. that I could see. The air circuit to activate the diaphragm is in the cover and is fed through the c.e. body where that small 1/8" gasket is located. Either of these could be partially blocked, and contributing to the pops. Manjo ~V~ 1111 1500A9
18.9. As you can see, the pilot jet size, the needle and slide, and the main jet, are critical to the performance of the engine at idle, through the mid-range speeds, and through the top end speeds, respectively, with the pilot jet having a continuous effect throughout all rpm’s.
18.10 Extreme care and diligence must be taken whenever changes are made to any carburetor setting in response to permanent changes in the air intake system or the exhaust system. Changes to the volume of air passed to the carburetors by the air intake system, and the back pressure to the carbs created by the exhaust system can have a profound effect on overall engine performance.
18.11 A too lean air-fuel mixture can cause the engine to overheat and reduce top end power. A too rich mixture will cause rough running and stalling. When rejetting BUBF carburetors, usually a larger main jet is installed to increase fuel to match an increase in air flow volume to the carburetors. The same is true for the pilot jet, but the pilot jet is changed less often since it can be "adjusted" to flow more fuel by turning the pilot jet screw outward, although after 4 turns out, the pilot screw has less and less effect on fuel flow to the idle circuit. In some applications where the air flow has been maximized, and larger main jets have been installed, a larger #45 or even #48 pilot jet are needed to provide good low end engine performance off idle.
A stock 1995 A comes from the factory with #112 and #115 sized main jets in the front and rear carburetors, respectively. A #42 pilot jet is used in both carburetor. The main jets increase in size (i.e., #118, #120, etc.) as do the pilot jets (i.e., #43, #44, etc.). A major air intake increase will require larger #140 main jets and larger PILOT JETS. Take a look at the Survey section of over 45 REJETTED BUBF's.
Then open the page COMBINED MODS for a subset of these bikes that have been rejetted for both the air intakes changed and after market pipes.
Here's a page with some BUBF REJETTING Theory that may be of help.
TECH TIP: I think a 170 jet is a 1.7 mm hole. To get to English units you would divide the jet number by 100 to get mm, divide by 25.4 to get inches. A 159 jet would be 159/100/25.4= 0.0626 inches, a 1/16 drill is 0.0625, close enough for government work.
52 gauge drill is 161 jet; 51 gauge drill is 170 jet; 1/16 drill is 159 jet; 1/32 drill is a 79 jet; 1/64 drill is a 39 jet; 1.5 mm drill is 150 jet. Later, Trent VROC 2071, 1999 VN750 "Marlin", earless and lovin it
18.12 Just a little more information on the location of the pilot screw. On the left side of the bike, you’ll see the rear cylinder carb. On the side of the carb facing you, you’ll see the brass cover (about 3/16ths inch in diameter) over the pilot screw, if no one has removed it already. On the right side of the bike, you’ll see a round chrome "carburetor cover" about 3 ½ inches across. Just unscrew the cover for a clear view of the front cylinder carb. The pilot screw has a small brass cover over it ( VROC archives has a write up for removing the brass cover) which is to the lower left as you face the carb on the bike. When you turn the pilot screw in to get to "seat completely," do so very carefully so that the shoulders of the screw does not score the seat or itself. Put a small pencil mark on the carb at "zero/bottom," that you can use as a reference as you turn out the pilot screw .
18.13 By turning the pilot screw OUT, you are increasing the fuel flow to the idle mixture (richening the mix). By turning the pilot screw IN, you are decreasing the fuel flow to the idle mix (leaning out the mix).
18.14 One quick mention of the choke or really the enricher. Rather than closing off the flow of air to the air-fuel mixture, when you pull the plunger out, you are increasing the amount of fuel going into the idle mix. Simple but important difference. It has been recommended that you should push in the plunger shortly after the engine starts to avoid carbon build up due to the rich mixture.
18.15 Here are links to pictures and diagrams of CV carbs:
http://www.f6rider.com/VRCC/tech/carb101.htm A very good start.
13. What air intake mods are available for 1500A/B/C? return to Master Table of Contents
13.1. The stock air intakes (ears on the side of the frame near the steering head) provide less air to the carburetors compared to after market air intake systems. As a result, your carburetor fuel/air mixture may be running richer than needed. An overly rich fuel/air mixture implies that you’re not getting the most efficient air-fuel mixture burn and therefore lower gas mileage and possibly less power. And during the engine's intake stroke, it's possible your engine does not take in the maximum air-fuel mixture volume. After market air intakes will provide more air to the carbs per unit of time. With more air available to the carbs, you will need to reset the pilot mixture screw and install larger jets in both carburetors to provide more fuel to the mix to avoid the other side of the air-fuel mixture "coin": an overly lean fuel mixture condition which over time can damage your engine. Air intake kits for the 1500A/B/C are made by Cobra (OEM is DynaJet), and Thunder Manufacturing (dual Hyperchargers made by Kuryakyn). The Cobra air intake kit includes jets. Both kits are available through distributors. NOTE: 1500 Vulcan owners including BUBF owners should avoid using the carburetor needles that come in these kits. The kit needles reduce overall miles per gallon dramtically. You would do better to continue using your STOCK needles.
13.1.1. There are also proven "do it yourself" techniques with write-ups for removing the stock air intakes and installing less restrictive K&N air filters. Noted below are the George Koppmann and Wiredgeorge (aka George Lesho who supplied the TECH TIP ear shave procedure listed in this section below) techniques where the stock air intakes are removed (ear shave), the black plastic surge box removed, and the remaining black rubber air tubing passageways shortened. The K&N filters are attached to the carbs using the shortened black rubber tubing.
13.1.2 A more recent, and less involved, technique is the Double Dutch stock air filter replacement where K&N filters are installed on the stock air intake base plates on each side of the frame with custom made brackets. This technique is a less extensive change to the air intake system (i.e., leaves the surge box and tubing unmodified), requiring only 1 to 2 hours to complete. The link to the archived Double Dutch technique is listed below. Go to www.vroc.org Archives and do a search on "msg08766.html" for details
13.3. GEORGE KOPPMANN has archived a series of posts detailing how to replace the stock air intakes with K&N air filters. He details the removal of the stock intake system and suggests the proper jetting to match the increased air intake in order to avoid a "too lean," air-fuel mixture problem. Go to www.vroc.org Archives and do a search on "msg08283.html" for details.
13.4. There are gurus out there that practice the black arts of carburetor adjustment by feel, touch, and smell (taste?). They can get a scoot into top performance because of their years of experience and accumulated knowledge with different air intakes, carb kits and settings. If you follow the VROC newsgroup posting or submit a carb question, you’ll be able to tap into this important information and knowledge resource.
13.5. For us, the less gifted and less experienced, there are two available and accepted tools to help us tune our scoots. The first is the Colortune (~~$40.00) and the other is an emissions gas analyzer. Colortune is a special spark plug with a clear glass view port that screws into either spark plug hole on an engine cylinder. You can actually see the colors of the air-to-fuel mixture combustion (or burn). You then compare the combustion colors observed at idle, and various throttle positions/rpm's to the kit's color chart to determine a lean, rich, or correct air-fuel mixture. If indicated, you would adjust the fuel mixture screw or re-jet the carb as needed to correct a too lean or too rich air-fuel mixture problem as viewed through the Colortune.
An emissions tester (~~$150.00 on up) is similar to the tester used in garages when they inspect your automobile (and your scoot, as in CA and other states) for exhaust emissions. A sensor probe is inserted into the tail pipe and the emissions tester records the carbon particulate count with a high emissions count indicating an incompletely burnt air-fuel mixture. Check the VROC Distributors page on the VROC home page for distributor names and numbers for air intake kits and fuel mixture testers. Prices vary for each.
13.6. Although less precise, the color of each spark plug is a good indication of the air/fuel mixture. A chocolate or brown cardboard color indicates a full clean burn and is recommended in the BUBF service manual. A light gray to chalk white color indicates a lean condition and dark brown or black indicates the air-fuel mixture that is too rich. Read more about BUBF spark plugs here.
13.10 TECH WRITE-UP: Following is step by step on doing the ear shave (i.e., the process of replacing the stock chrome covered air intake filters with K&N less restrictive air filter elements directly attached to each carburetor (while doing coasters as well) on a BUBF (1500A/C).TECH TIP: Man, don't guess about jetting........read the plugs. I'm running a 118 front and a 120 rear but that has nothing to do with the way your motor is running. If your plugs are black, the jets are still too big. If they are white or gray powdery, too lean. My guess is that you are still too big or rich on the jets but don't go by my guess either, read the plugs. You want them about the color of cardboard. There is an archive with pictures on reading plugs. Good luck. Dutch ~V~ 1009 Teal/Blue A8 88 Federal Way, WA
Parts:
- K&N Air Cleaners 2 ea. P/N RU-0982 or RC-0982 single input crankcase breather filter kit (bracket and filter)
- small and very small hose clamp assortment (about 6 each)
- Black RTV
- Sheet metal screws (4 ea.)
- 2" diameter PVC spacer (3 inches long)
- wire ties 12 ea.
- 140 Main Jet 2 ea.
- 48 Pilot Jet 2 ea.
- hardened carbide 3/64 drill bit
- coasters 2 ea.
- manometer
PARTS NOTE!
I suggest you buy your jets and filters from Carburetor Parts Warehouse, near Cleveland (they will be about the only distributor to have both IN STOCK):
Carburetor Parts Warehouse will sell you whatever size jets, and a few other parts for the Keihin CV Carbs and Mikuni Carbs; and K & N Air Cleaners to fit whatever specs you're attempting to meet.
Carburetor Parts Warehouse
, 7777 Wall Street , Valley View, OH, USA 44125, (216) 524-1599, http://www.carbparts.com/Step by Step Details:
- Remove seat, tank, side covers, ears (existing air-intake covers and filters).
- Unscrew and remove the round decorative cover located over the right side carb. Locate the silver plug situated next to what appears to be a brass plug on each carb. Use the 3/64 drill bit and drill a small hole in this silver plug. Take a scribe or nail and pop the plug out. You will find a pilot screw head under the plug. Turn the pilot screw all the way in, then back each screw out two full turns. Repeat for the other carb.
- Undo gas pump (remove the two bolts retaining it to its mounting bracket but leave hoses connected) and balance carbs
NOTE! Get a manometer to balance the carbs before rejetting. A manometer is a carb sync tool that has mercury in plastic tubes and hoses that attach to the other end of these tubes. Refer to a shop manual, Clymers or the instructions included with the manometer for the procedure for carb balancing (or the instructions included in these FAQ pages linked to 26. Miscellaneous).
NOTE! If you have a Clymers manual, the picture (in carb sync section) in chapter 3 purporting to show the location of the vacuum ports is INCORRECT! It DOES NOT show the vacuum ports. The hoses shown are actually air vents which connect to a 2 into 1 collector wired tied to the right frame member with a vent tube exiting it which is routed under the seat. These hoses will not be touched in this job. In fact, it is critical that these hoses not be plugged or obstructed in any way or the carbs will run roughly.
Back to the vacuum lines:
One vacuum port is located under the fuel pump you loosened. It is joined to a four way plastic ‘T’, which connects to the other vacuum port, located on the right side of the bike on the front/top of the front cylinder carb. The other two plugs go to the 'EPA cans'. EPA cans are the brass colored cylinders with a bunch of hoses coming out of them and are tied into the bikes vacuum lines and reed valves.
- After balancing the carbs, cap the vacuum plugs. Then, take off the 2 plastic frame covers which are directly behind your steering head which cover the water pump. There are three screws; one on each side and a screw on the top.
- Drain the radiator. There is a plastic plug on the bottom of the radiator. Undo the radiator cap so the antifreeze will flow. Collect the antifreeze in a clean container for reuse. If you use new anti-freeze, use the kind that will not corrode aluminum (i.e., the type that contains no silicates that will wear away aluminum) and be aware antifreeze works more effectively as a solution (roughly 50% distilled water and 50% antifreeze). Check the mixing instructions on the antifreeze container label for the brand of antifreeze you select.
- Remove the four hoses connecting the water pump and remove the water pump. You can now pull the top bolts holding on the radiator and swing it forward. This will allow more room for removing the stock air box.
- Pull all the hoses off the EPA can in front of the front cylinder. DO NOT pull the hose coming from the crankcase off its plug. It is used later. Remove the EPA can.
- Install the front coaster. The coasters I bought from Drew Arnone, VROC-793R, included decent instructions. Use the existing reed valve gasket if it doesn't break or Hi temp RTV (Form a Gasket can also be used).
- Install the crankcase filter bracket the crankcase breather hose (remember it from step 7?) to the crankcase breather filter and insert it into the bracket. Clamp the hose to the filter using a small hose clamp.
- Remove air box. It is a tight fit but will come out at this point. You may need to cut some wire ties if cables routed down the frame obstruct removal.
- Install rear coaster. Again, use the existing reed valve gasket or RTV to seal the coaster to the cylinder head. Also, check again that when you remove the vacuum lines, to cap off the vacuum ports on the carbs using a piece vacuum hose with a bolt in it.
- Remove battery. This is a good chance to top the battery off with distilled water, clean the terminals and put some Vaseline on the terminals.
- Remove rear EPA can located just in front of where the battery had been.
- If the inlet tubes that went into the airbox are still on the bike, remove them and set them aside. These tubes will be used later.
- Using a 7mm wrench remove the two bolts holding on the bottom of the carb. Using an 'L' shaped screwdriver, remove main jet which is the lowest jet protruding from the bottom of the carb. Replace with new 140 main jet. A good trick is once the jet is broken loose, use a 1-inch piece of vacuum line placed over the jet to screw it out. Your fingers will get in the way here! Now remove the pilot jet which is next to and above the main jet. Replace it with a 48 pilot jet. Carefully replace the carb bottom so the rubber seal doesn't leak gas. Repeat on other carb.
NOTE!: Do yourself a favor and get a 7mm 'L' shaped ratcheting flat blade screwdriver
blade -> |_____________ <- ratcheting handle
The 'L' Shaped screw driver will be very useful for removing the jets. A regular small screw driver doesn't have the leverage to break the jets free easily or tighten them up well (IMHO).
- Cut off the end (not the one that attaches to the carb but the one that will attach to the filter) of the U shaped carb to airbox duct. Cut as little as possible. This will be used to attach the front cylinder carb air cleaner. The rear cylinder air cleaner can be attached directly to the carb. Install a 3 inch long piece of PVC, 2" diameter (its for 2 inch ID therefore it is a shade bigger outside diameter) in the cut end of the U shaped duct. This gives the air filter a more positive clamp surface. Slide the PVC spacer into the cut end of the duct and use sheet metal screws to fasten these parts together. Using this duct, you will need to remove about an inch of the rubber divider that is used to keep this longer tube from collapsing. Apply RTV around the joined area to seal it. You may wish to grind down the exposed PVC end (the one the air cleaner will slide on to) a bit as the filter fits on very tightly or you can work the filter onto the end of the PVC more easily. Install the new filter units onto the carbs.
- This is a good point to check the routing of cables and hoses and wire tie the stuff so it won't chaff. Make sure that gas hose is kept off the manifolds and route the gas hose from near where the fuel filter is between the frame members so it won't get crushed. Many of the cables and hoses were not routed well from the factory so this is your chance to improve the routing to protect the cables/hoses. Also examine the wires coming out of your headlight and examine for chafing. Correct the situation, if necessary.
Note! Most 1500A,B, C owners have had no luck installing after market jet needles and the stock ones have been found to perform best. You can also use a 1/8 inch drill bit to drill the vacuum port on the slide to enhance throttle response. Many owners have done this and some feel it is worth the effort and some don’t. You can also shorten the slide spring to also enhance throttle response. My personal feeling is that it is best to NOT REMOVE the carb top any more than necessary as the thin rubber diaphragm is difficult to reseat and if it pinches and ruptures, it is costly to replace. If you do remove the carb top and drill the slide or shorten the spring, and have trouble reseating the diaphragm, put the diaphragm in the freezer to stiffen the rubber and it will be easier to replace under the carb top.
Drop a note if you have a question. The set-up described will probably work fine but you may need to do some tuning as individual bikes behave differently and may require different main jets or a different number of turns out on the mixture screws. (lesho@bigfoot.com)
It would be a good practice to re-synch your carbs again. If you do not get a consistent balanced reading at idle, mid-range, and high-end throttle, (850, 2000, and 3500+ rpm’s) then you should check all the new filter and carb boot connections for possible air leaks. Wiredgeorge (George Lesho) ~V~2420, Mico, TX.
TECH TIP: Don't Plug tank VENT hose by accident: Don't know about the 1500s, but on the 800s, if the vent line is plugged, it will overpressure the fuel tank and carb, thereby forcing fuel into the engine and flooding it. Worse, this has a tendency to force fuel down into the crankcase as well, thus contaminating the oil. The Russian Wolf VROC #5268, FPI #3 Salcha, Ak, 1999 black Vulcan 800A RFQ, Scooterized & CruZeredreturn to Master Table of Contents
14. What carburetor mods and kits are available for the BUBF? return to Master Table of Contents
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