I have been continuing with the cleaning and rebuilding of the four carburetors. A slow going process mainly due to the soaking time required for each carburetor to get all of the carburetor passages clear before rebuilding each carburetor and only space in my parts cleaning bucket for one carburetor at a time (Don’t want to swap parts between carburetors either). Now all four carburetors are cleaned, o-rings replaced, gaskets replaced, rebuilt, and float tested.
The carburetors were already removed from the bike when I bought it, so everything I do I am looking for clues to what might have been the issues before the previous owner stopped riding this bike, but some of the things that I am seeing could just be because the bike has not been run for a few years.
Here are some of the things that I found during this process:
All carburetors had the float valve plunger (red circle in photo) sticking and pilot jet orifice (green circle in photo) clogged. The plunger is spring loaded and took long soaks and carb cleaner spray to free them up. Not sure this would have had much effect on the running of the engine, but the float valve in carburetor four was completely stuck in its valve seat. Either no fuel was getting into that carburetor or it would never stop filling up. The clogged pilot jets would have been affecting the the low speed range of the engine.
All four carburetors also had the starter circuit or choke circuit completely clogged. Therefore the bike was probably hard to start without being able to richen the fuel mixture. This circuit is shown in the following picture. The red circled fuel pickup on the left inserts into the red circled passage on the float bowl body on the right. The float bowl then has a passage way between the red and green circles to pick up extra fuel when the choke is engaged. Lots of soaking, carb cleaner, and poking with a wire to get these passages reopened.
The last item during the tear down was removing the piston slides of the diaphragms. The picture below is an early shot of the four carburetors before the tear down. The piston slides are the gold tubes in each carburetor. Carburetors one thru three were just a little tight to remove. A gently pry with the wooden handle of paint brush popped them right out. Carburetor four was really stuck again though. The wooden handle of the paint brush broke on the first attempts. A day of carburetor cleaner spraying and gently prying with a plastic handled paintbrush got that diaphragm out. Again, a fuel mixture/volume issue with this carburetor. After soaking the carburetor bodies in parts cleaner, all four diaphragms move up with just light finger pressure and return to seated on their own with the proper motion.
When putting each carburetor back together, most everything just gets tightened until fully seated. One of the items to adjust is the float bowl height. The photo below shows a before adjustment picture on the left and after adjustment picture on the right. The specification is 22.4mm +/- 1mm for the float height measured from the gasket seat. All floats measure low and were adjusted with an imprecise method of bending the metal tang of the float bowl arm that presses against the plunger of the float valve shown above. The carburetor are upside down during this measurement, so if the float position is low, the fuel level in the bowl will actually be higher than desired. Running rich again and possibly flooding with how low these floats appear to have been set.
At this point, all four carburetors are back together. The last item adjusted on each carburetor, but not shown here was the pilot screw on each carburetor. For these, I screwed the pilot screw in until lightly seated and then backed them out 2.5 turns as a starting point for the idle mixture. This will get adjusted again on each carburetor once the carburetors are installed, engine running, and carburetors vacuum balanced.
Although the floats were adjusted to specification above, it is much better to actually test the fuel in the float bowl by attaching a clear piece of tubing in place of the float bowl drain plug (service manual does this test with the engine running). In this test, you are looking for the fuel level to be 5mm +/- 1mm below the bottom edge of the carburetor body. Here is the test setup with an auxiliary fuel tank and the carburetor leveled in a vice. There is only about 1/4 gallon of fuel in the tank, but it was hanging from the ceiling to get some head on the fuel line which will also make sure your float valves are working properly.
Surprisingly, even though I raised the height of each float before putting the carburetors back together, the floats were still too low. One more round of adjustments and each carburetor is right on 5mm below the carburetor body.
So it’s getting there. Still a few things to do before reinstalling the carburetors to the bike:
- Gang the carburetors back together.
- Bench synchronize the four carburetors.
- Remove the intake boots from the cylinder head and replace their o-rings.
- Replace the clutch cable.