We’re starting a series to document the revival of this CB175. It’s not exactly a barn find, more of a garage re-discovery. We’ll show you the steps taken to get it back on the road. I’m at the owner’s garage for this job and he doesn’t have a lift, so some of this will be slightly awkward.
First off, we have to get the fuel system clean. That entails cleaning the rust out of the gas tank and cleaning and rebuilding the carburetors. We’ll also inspect the throttle cables and twist grip to assure smooth operation.
This gas tank isn’t badly rusted, so it should clean up with minimum effort. There are several ways to remove rust, and I prefer to start off with the least aggressive method and ramp up if needed.
We’re going to be using a non-corrosive de-rusting agent so simple rubber caps can be used to plug the crossover tube on this Honda tank. You can usually find packs of these at automotive parts stores sold as vacuum caps.
We used duct tape to seal off the petcock hole, but it didn’t work as well as expected. Since the cleaner is non-corrosive, you could just leave the petcock on and remove it for cleaning after you clean the tank.
PB Blaster makes a concentrated de-ruster, you mix it with water to create the quantity of cleaner you need. If you have a suitable container, you can re-use the mix until it stops working, at which time you can pour it down the drain as it’s not a hazard to the sewer treatment system.
Once you’ve got the quantity you need for the job, fill the tank to the brim and let it sit overnight, at least. The time needed for it to work depends on the level of tank rust. Ours was surface rust, so overnight was enough to completely clean the tank.
The overnight results: Clean metal ready to be used as a gas tank once again. Tanks with worse rust will take longer but eventually produce the same results.
The next step in cleaning out the fuel system requires us to clean and rebuild the carbs. For the removal steps use 10mm and 8mm wrenches. 10mm to remove the air filters and 8mm to remove the carburetors and manifolds from the engine.
You may find that the rubber parts of the air filters are stiff with age. A heat gun on low will soften them up. If you don’t have a heat gun, a hair dryer will do the job a little slower.
With the air filters removed, the next step is to remove the carburetor tops and throttle slides by unscrewing the carburetor tops.
Holding the cable and carburetor top in one hand and the slide in the other, compress the spring to allow the throttle cable to slide up and then thread it through the slot on the slide to release the assembly from the cable.
With the throttle cables free of the carburetors you can now move on to removing the carburetors from the engine. An 8mm combination wrench works best for this.
After you have all four nuts off the studs, remove the carburetors as an assembly from the right hand side of the bike. The carburetors are only joined by the choke linkage so you have to support both carburetors as you remove them.
It’s always a good idea to plug the intake holes to keep any spare parts or flying insects from entering the engine.
We begin the carburetor rebuild by removing the float bowl for access to the float valve and jets. On this CB175 the bowl is held in place by a spring bail. Other carburetors will have screws holding the bowl in place.
The first part to remove is the float assembly held in place by a pivot pin. You can usually push the pin out with a scratch awl or thin wire brad (nail).
The main jet may be removed with a suitably sized screwdriver. As the jet is soft brass, getting the screwdriver blade the right size can keep it from slipping out and marring the slot. You may need an even smaller screwdriver for the idle jet.
Continue by removing the old gaskets, bowl and intake. Compare them to the new ones in your kit to confirm sizing.
Now we have the two carburetors stripped and ready to clean. That’s all we have room for this issue, stay tuned next issue to learn how to put a carburetor back on a motorcycle after cleaning as we continue our quest to get this CB175 back on the road.
