[/center]This how-to describes the process required to disassemble, clean, inspect and reassemble your carburetors, replacing common wear items including screws and o-rings. This process is typically performed as part of carburetor maintenance and does not include butterfly-shaft removal or butterfly seal replacement.
Symptoms:
How do I know when I need to clean or rebuild my carburetors? Here are Some General Symptoms that your carbs require maintenance:
- 1. Your Seca II is hard to start or floods easily.
2. Your Seca II leaks fuel out of the carburetors.
3. Your Seca II won't idle without the chock on.
4. Your Seca II's idle speed is difficult to set and the bike hunts for idle.
5. Your Seca II won't run without consistently giving it throttle.
6. Your Seca II idles low and turning the idle screw makes it jump up to 3k rpm.
7. Your Seca II has trouble idling; it may die at stoplights or when the clutch is pulled.
8. Spark plugs are wet with fuel
9. Spark plugs are dry and bike won't start but has good spark.
10. Your Seca II has been sitting for along while and will not start.
Before we begin the rebuild and cleaning process, let's go through a few key terms that will be used during the process. Below are several views of the assembled Seca II carbs with names of common parts:
Workspace Preparation:
Prior to beginning the cleaning and rebuild process, set up a clean workspace and ensure you have all tools and parts ready. I typically will lay out a piece of cardboard and disassemble the carbs on that. It keeps things clean and helps me keep track of small parts. Additionally, if you are working on a set of carburetors which have recently had fuel in them, be sure to fully drain them and allow them to dry out before disassembly.
Service Precautions:
Gasoline is extremely flammable. If the carburetors you are cleaning have recently had fuel in them, drain them thoroughly and allow them to dry-out prior to undertaking this procedure. Keep a fire extinguisher nearby and work in an area with ample ventilation and without an ignition source (such as a pilot light or furnace). Any paper towel or rags used to mop up spilled fuel should be kept away from ignition sources and properly disposed of afterward as fuel soaked towels can self-combust. As with any procedure, do not undertake this process if you are not confident in your ability to complete it safely.
Tools Required:
The following tools are needed to disassemble and clean a set of Seca II carburetors:
- #2 and #3 JIS Screwdriver - The screws used on the carburetors are JIS screws. The small dot indentation on the head indicates that these are JIS screws. While JIS screws look like Phillips head screws, they have different internal angles and shapes and a Phillips screwdriver will almost always strip them out. Buy a set of JIS screwdrivers prior to disassembly.
- Small flat-blade screwdrivers - Used to remove the pilot screws.
- Flat-blade screwdriver - Used to remove the pilot and main jets.
- 6mm bit driver - Used to emulsion tube brass acorn nuts.
- Thin-walled, deep-well 12mm socket - Used to remove the enrichment plungers.
- Needle-Nose Pliers - Used to remove float pivots.
Parts Required:
The following parts should be replaced during the cleaning process. Note: This procedure does not remove or replace the butterfly seals.
Seals and Gaskets:
- Fuel rail connector seals - Yamaha P/N: 3EN-14997-00-00. Six (6) are required.
- Float valve needle - Yamaha P/N FN-14107-12-00; sold as a set with the seat - Four (4) are required.
- Float bowl gasket - Yamaha P/N: 1HX-14147-00-00. Four (4) are required.
The following o-rings are required. These can be attained as a kit from this site.
- Float valve seat o-ring - McMaster Carr P/N 9262K122
- Main jet o-ring - McMaster CARR P/N 9262K511
- Pilot screw o-ring - McMaster Carr P/N 9262k441
The following replacement screws are required to replace your stock screws (if they are damaged during disassembly). These can be attained as a kit from this site.
- (2) 5mm x 1.0 x 12mm long Phillips-head screws (enrichment bracket to assembly bracket)
- (18) 5mm x 1.0 x 10mm long Phillips-head screws (assembly bracket to carb body)
- (3) 4mm x 0.7 x 16mm long Phillips-head screws with lock washer (throttle bracket to float bowl)
- (17) 4mm x 0.7 x 14mm long Phillips-head screws (float bowl to carb body)
- (12) 4mm x 0.7 x 8mm long Phillips-head screws (carb top to carb body)
Follow this procedure to remove the carburetor assembly from the bike.
Disassembly Procedure:
Once you have all of the necessary parts, a clean workspace and a set of dry carburetors, its' time to disassemble the carburetor assembly. Begin by laying the assembly with the carb-tops facing downward. Using a JIS screwdriver, remove the idle-speed adjustment screw:
The adjustment screw contains a spring and a nylon washer. Ensure these parts are removed when the screw is removed:
Once the adjustment screw is removed, use your JIS screwdriver to remove the three screws which hold its bracket to the carburetor float bowls:
And remove the bracket. Place the idle adjustment screw and its bracket together and sit aside:
Flip the carburetor assembly over so that the carb tops face upward. Using your JIS screwdriver, remove the four screws which secure the throttle-cable bracket to the carb tops:
Lift off the throttle-cable bracket and sit aside:
Rotate the carburetors so that the enrichment knob is facing upward. Using your JIS screwdriver, remove the two screws which hold the enrichment assembly to the carb bracket:
Slide the enrichment knob out slightly and locate the c-clip that secures the lever to the slider:
Using a flat-blade screwdriver, very carefully press downward on the c-clip and remove it.
Remove the enrichment knob and sit it, the enrichment assembly and the c-clip aside:
With the enrichment assembly removed, the enrichment slider can be removed. Use your JIS screwdriver to remove the four screws which hold the slider to the each enrichment lever:
And carefully pull the slider from the carb assembly:
Lay the slider with the enrichment levers and sit them aside:
Rotate the carburetor assembly so that the carb tops face upward. Using your JIS screwdriver, remove the screws securing the carb top to the carb body:
With the screws removed, the carb top should pop off easily. Lift the carb top upward:
Then remove the slide spring:
Below the slide spring is the slide and diaphragm. These parts are both expensive and fragile. Use extreme care when removing, storing and cleaning them:
To free the diaphragm, gently pinch it with your fingers and lift upward. This will remove it from the groove in the carb body:
Work your way around the diaphragm and lift it up fully:
Then pull the slide free and remove the slide assembly:
Note which carburetor the slide assembly came from (it must be installed back into the same carb body it was removed from) and sit it aside, keeping it paired with its spring and carb top:
Repeat the process for the remaining slides:
With all four slides removed, flip the carb assembly over so that the float bowls face upward:
Using your JIS screwdriver, remove the four screws which secure the float bowl to the carb body:
And lift the float bowl free:
Repeat the process for the remaining float bowls:
Using a small screwdriver or other suitable tool, gently push the float pivot hinge to the right:
And remove the float hinge:
With the hinge removed, lift the float free. Note that the float needle valve will come out with the float. Sit both aside:
Repeat the process to remove the floats and float valves from the remaining carbs:
Using a 6mm socket, remove the brass acorn nut securing the emulsion tube:
Ensure that both the acorn nut and the brass washer are removed and sit aside:
Using a suitable tool, gently push the emulsion tube downward to free it from the carb body. The tube will fall through the carburetor and will land on the cardboard. As with the slides, the emulsion tube must be placed in the same carb body from which it was removed. Sit it with its corresponding parts:
Using your JIS screwdriver, remove the screw securing the float valve seat to the carb body. Be very careful with these screws as they are easily stripped:
Then, using only your fingers, grasp the needle valve seat:
And lift it from the carb body. Use a back-and-forth wiggle motion while pulling upward to free it from the carb body. Place the needle valve seat with the other parts from the same carb. If you cannot remove it by hand, leave it in place and try again after the first-round of cleaning. DO NOT attempt to remove the needle valve seat with a pair of pliers.
Using a tool which fits into the slot on the main jet, very tightly (I use the back-edge of a butter knife), loosen the main jet:
Then carefully unscrew it:
And remove it from the jet holder. Note the black o-ring which is attached to the main jet in this photo. This is the main-jet o-ring and should be removed with the jet.
Using an 8mm open-end wrench, loose the main-jet holder by grasping it where it screws into the carb body:
Unscrew the main-jet holder and remove it. Ensure that the small copper washer is removed with it:
Repeat the previous steps to remove the jets from all four carburetors:
Using a JIS screwdriver, remove the 8 screws securing the assembly bracket to the carb bodies:
And remove the bracket:
Using a JIS screwdriver, remove the four screws securing the front bracket to the #2 and #3 carbs:
And remove the front bracket:
Then carefully separate the #1/#2 carbs from the #3/#4 carbs:
With the carbs separated, remove the fuel tee: (Note that this one has a bunch of rand o-rings on it which are not supposed to be there)
Remove the four screws which hold the #1 and #2 carb bodies together:
And remove the bracket:
Separate the #1 and #2 carb bodies:
Remove the fuel-connector: (Note that this one has a bunch of extra o-rings on it that aren't supposed to be there)
Here is what the connector is supposed to look like after I've removed all the o-rings:
Then remove the vent tube:
Repeat the preceding steps and separate the #3 and #4 carb bodies:
Using a thin-walled deep-well, M12 socket, loosen the enrichment plunger:
Unscrew the enrichment plunger and remove it. Ensure that the plunger, spring and cap are all removed and sit aside. As with all of the other parts, the enrichment plunger must be installed back into the carb body it was removed from.
The last step in disassembly is to remove the pilot screws. If you have brass-plugs over your pilot screw, then your cabs haven't been fully disassembled before and you need to remove the brass plugs to access the screws. If your pilot screws do not contain the brass plugs, you can skip ahead a few steps.
The pilot screws are located beneath the brass plugs. The plugs need to be removed to access the screws:
Using a 3/32" drill bit, carefully open-up the hole in the center of the plug. Do not drill deeper than 1/4" or you will damage the screws beneath the plug:
Once the hole is opened up, thread in a #10 machine screw:
And use a pair of Vise Grips to grap the screw and remove the plug:
This is your pilot screw:
Use a small flat-blade screwdriver to screw the pilot screw inward until it seats. As you do this, count the number of turns until it seats and write that number down. You will set the pilot screws to this position when you assemble it:
Once you have counted the number of turns to seat your pilot screw and written it down, remove the pilot screw:
Typically, the washer and pilot screw o-ring stick inside the carb. If they do not come out with the screw, use a small drywall screw to fish them out:
Ensure that the pilot screw, spring, washer and o-ring are all removed and sit them aside:
Repeat the preceding steps and remove the pilot screw from all four carb bodies. Here is my workspace with all of the carburetors fully disassembled. Note that I've kept track of which parts came from which carb and also wrote down the pilot screw settings for those carbs. Your work are should look similarly when you are done:
