Assuming your carbs were put-away wet, and have deposits caked in their small passages and brass jets, you can do a bit more to see your bike run properly. First, be ready, and take pictures, lots of pictures, every step of the way. Make sure they're in-focus and that they identify what you're doing, so you can reassemble the carburetors properly. One way to help do this is to replace whatever you're working upon, immediately, as you're removing it. That way, you show yourself exactly what you're doing, how it goes back together, and you're building muscle-memory as you reassemble things. Label parts, and use something like small baggies and masking tape with a fine-point Sharpie permanent ink pen to label parts and the baggies.
To remove the carbs, you need to disconnect the cables. I do this at the junction box, the white plastic piece where the upper throttle cables mate to the lower throttle cables. It's behind the left aluminum airhorn. Note the cable routing, take a picture so you know where the junction box is positioned, Improper replacement may cause throttle cable jamming or sticking, leading to a WFO throttle! Don't strip-out the tiny screws, and don't drop them! Some pieces of this assembly are unavailable from Yamaha. You will notice that as-long as the upper throttle cables stay attached to the twist grip, the cables at the junction box can only be reassembled in one way. Still, it's a good idea to use 4 pieces of masking tape around the cable sheaths, the jackets, to I.D. them for reassembly. After you do the removal/replacement a couple of times, it will be easy to recall what goes where, and especially if you label things. Remember my suggestion to immediately reassemble something as you take it apart, to make it easy to recall the proper method and sequence as everything is reassembled after servicing.
To remove the carbs, I use a long length large screwdriver or you can use a prybar, but
be careful where you pry! Carburetors are potmetal, they are notoriously
easy to break, and a careless attempt at prying can break a body! Some bodies are now listed as 'unavailable' on the Yamaha parts fiche! Once the clamps are loosened, a spritz of WD-40 at the top of the VBoost rubber donuts-to-carbs may aid you in getting them off.
You remove the 4 carburetors as a set. You split the carbs into two pairs by removing the stamped-steel brackets which look like girders. This allows access to the float bowls. One screw on each float bowl will be a 'security' screw. Three ways to address this:
- use a Dremel to cut a screwdriver slot into the security screw so you can use a screwdriver to remove it.
- use a straight-jaw Vise-Grips to grab the screw head, to loosen it. Replace that screw with another, many here use allen-head screws for ease of torquing on delicate carburetor bodies.
- buy the Harbor Freight security screw bit set.
https://www.harborfreight.com/security-bit-set-33-piece-68459.html
Once you're in the carburetor float bowls, remove the jet block. The two brass jets inside the passages need a narrow-head slot screwdriver to remove them. The pilot jet you will likely discover to be plugged solid with varnish and/or rust particles from a rusty gas tank. I use a pin vise, and a single strand of SS wire to gently ream-out the pilot jet hole. Do the other jet, too, after removing it.
The pilot jet w/a SS wire used to open an obstructed passageway in the jet:
Spray all the passages in the carb bodies with carb cleaner. I use an an ultrasonic bath, but carb cleaner and compressed air often will work.
The gasket under the jet block usually will tear apart when you attempt to remove the jet block after removing its screws. Once its screws are out, carefully using a pick like the ones below, to attempt to break the seal between the carb body and the jet block and its gasket, may save the gasket from tearing. I admit to saving jet block gaskets which haven't torn, in a small baggie labelled as to what bike they go to, for emergency use in the future. It stays with my carburetor stuff. The cost-effective carb gasket replacement is the K&L kit. OEM is of course, always correct, but piece-by-piece they can get expensive.
DO NOT BUY THE 'ALL FOUR CARBURETOR REBUILD KITS ON EBAY OR ELSEWHERE! They don't fit, they are substandard, and will cause you hours of grief as you attempt to make them work!
Check your 'dry' needle valve gas inlet float level. See the illustration for putting the float just at the top of the carb body's O casting. bend the tang of the float slightly to get the float in its proper position.
Some people complain about the gas inlet needle valve and its thin loop which goes over a metal piece of the float tang. "I bought a replacement kit, but it doesn't have that closed loop.' Or, " I can't get the closed loop onto the float tang and get it into the needle valve seat."
Yes, you can, if you're careful and you take your time. I usually place the needle valve into the needle valve seat, and then use a small pick or a dentist's pick to slightly remove it from the seat hole, and then carefully slip the tang into position.
https://www.harborfreight.com/mini-pick-and-hook-set-63697.html99 cents, sale ends today!
Don't forget those rubber corks for the jet block tunnels, they're different sizes.
Put your float bowls back on, and reassemble the carbs into a single set, using your pictures you took, and your labelled baggies and any notes you made about the disassembly.
Be sure that you get the carbs seated properly so they're fully inserted into the rubber boots of the VBoost. A smear of KY jelly or another water-soluble gel around the rubber boots inner surfaces will help the rubber boots to accept the bottoms of the carb bodies. Once fully-seated, snug their bands until you reach the snug point. If you look at the clamps, you'll notice there's a small metal tab which is a limiter on how tight you can get the clamps.
You need the air cleaner on the carbs, and that requires also ensuring the rubber donuts from the airbox to the carb tops (usually referred to as their 'bellmouths') are fully-seated. You need the resistance to airflow of the carb air cleaner for the engine to rev. You may be able to start the engine and have it idle, but without the air cleaner, an attempt to rev the engine will just make it 'blubber' and it won't rev.
https://www.vmaxforum.net/threads/seat-those-carbs-easily.21303/
https://www.vmaxforum.net/threads/tricks-to-plug-the-carbs-back-in.35378/
With your cables re-connected at the junction box, ensure that your throttle is not binding, and that your throttle is smoothly operating, and returns to its 'closed' position.
Hook-up your gas line (this is a good time to match up your OEM filter at your local auto parts store and to replace it) and try starting your engine. It's always good to do this outside and away from any flammable material, or a potential source of ignition like a gas-powered water heater and to have a functional fire extinguisher nearby.
This is just to ensure that you have clean, unobstructed pilot jets and passages in the carbs, and hopefully, your bike will start and run, and rev. Since you're not doing a carb synchronization, the bike may not operate as-smoothly as it would from doing a proper synchronization, but if the passages are clear for both gas and air, you should be able to get it running.
This is not intended to be a complete carburetor overhaul, it's just a suggestion about getting your pilot jets cleaned of blockages, which will have an effect on being able to start and idle, and for low-speed operation, if those pilot jets are obstructed.
The all-important float level diagram, I think this is courtesy of
dannymax:
Additional references:
https://www.vmaxforum.net/threads/jet-block-rubber-caps.53017/#post-532263
https://www.vmaxforum.net/threads/carb-kits-questions.52635/#post-528887
CaptainKyle supplied this ebay link for the K&L kits above. I have also used this supplier. K&L makes OEM parts for the Japanese bike brands.
Here is the seller I usually by from they are very dependable.
Yamaha VMX12 VMAX V-Max 85-07 Basic Carburetor Repair Kit K&L18-2879 | eBay
https://www.vmaxforum.net/threads/carb-rebuild-kit.52488/#post-528680
