Clean the motorcycle carb jets and learn how to put a carburetor back on a motorcycle after cleaning with a Honda CB175 as a model.
Last issue we got the gas tank clean and the carburetors off the bike and disassembled as the first step in reviving a long-dormant Honda CB175. This time we’re going to clean the carburetors and reassemble them with some new parts. We got our rebuild kits from Matt Wiley at Moto-Vintage.
The jets don’t suffer any appreciable wear in use, so you can use the factory jets if you want. We are fortunate enough to have use of an Ultrasonic cleaner, so everything goes in for a 15 minute heated shake in a dilute mix of Simple Green and water. Carburetor cleaner is another option. Gloves and good ventilation are a must if that’s what you use.
The first step is to clean all the castings and the jets if you are reusing them. On the left, a grungy carb, as removed from the bike. On the right, a clean carb after the Ultrasonic bath.
Carefully check your replacement parts against the original parts. Although most of the replacement parts in our kits were exact replacements, the idle mixture screw and the throttle stop screw were not, and we opted to use the originals.
Using the appropriate sized tools, install the idle jet, atomizer, main jet, and the float valve seat. Don’t forget the aluminum crush washer under the float valve seat.
Install the new float bowl gasket.
Install the float needle and floats and slide the retaining pin in place. Check the float heights. Often you won’t have to make any changes if you just replaced parts. Factory settings are usually measured with the gasket removed, so keep that in mind too.
When the floats are set correctly, install the float bowl on the new gasket. Make sure the retaining clip is on the correct side of the bowl to be slid into locking position after the bowl is placed.
With the float bowl locked in place, you can replace the bowl drain screw and O-ring with the new drain screw and new ring.
Reinstall the idle mixture screw and lightly seat it, then back it out 1-1/2 turns. That’s a good starting point for idle mixture adjusting. Install the throttle slide screw and spring too.
Reinstall the throttle needle with the e-clip in the middle notch, then use the hairpin spring to secure the needle in the slide. Put the slides back in the carburetors and adjust the slide stop screw until the slide just starts to rise, then 1/2 turn more. This will give you a starting point for final idle adjustment and synchronization.
Bolt the carburetors back on the bike. Refer to our previous how-to if necessary and just reverse the procedure. Replace the choke linkage, washers and cotter pins that connect the chokes.
Remove the tops and slides. Position the top nut and carburetor top on the cable and then reinstall the slide on the throttle cable. Set the slides back into the carburetors and secure the top nut.
Now that we’ve got the fuel system clean, it’s time to check the oiling system and change the oil. We’re going to remove the cover of the primitive oil filter and inspect it. We’re using an impact driver to loosen the screws to avoid damaging the screws. If you have the proper JIS screwdrivers you may not need this step.
After loosening the three cross-point screws holding the cover in place, carefully pry it off using the slots provided in the engine case. Easy does it.
There are two O-rings that seal the cover to the engine case. Be sure you replace them both. They form a pressure seal that sends oil to the camshaft that runs in the aluminum head. I’ve seen too many heads ruined by leaving out an O-ring here.
The larger of the two O-rings should be rolled into place over the cover and seated in the groove in the base.
I find it easier to place the smaller O-ring in the cavity of the engine case. Use a little grease to stick it in place if it wants to wander.
Replace the cover, making sure the two holes in the cover match up with the holes in the engine case. The cover screw holes are not drilled exactly 120 degrees apart, so if you get the cover on and they don’t all line up, you’ve got it out of position.
Move on to draining the oil. Many times this drain plug will be over tightened, so some extra force may be needed to loosen it. Make sure you have a large drain pan at the ready to catch all the oil.
The dipstick lists the correct amount and weight of oil needed to refill the crankcase. Once you have refilled it, check the level with the dipstick.
That’s going to wrap it up for this episode, next time we’ll finish it up by showing you how to check the ignition points and how to change a motorcycle tire before going for a ride.
