So with most of my bike projects, I started by pulling the carbs....
The previous owner claimed to have cleaned them a few months before I purchased the bike. However, I know first hand that old CB750 carbs need more than a simple "cleaning". The throttle was also sticking at WOT so I knew something wasn't kosher. So, off came the carbs and down to the workbench where I could disassemble them and keep track of all the loose bits. Here are the carbs as they came off of the bike.
You may notice something off in the next pic. The carb plunger in the leftmost carb was not sliding in unison with the other 3 when the throttle linkage was moved. It was immediately apparent that this wasn't going to be a routine cleaning. From here on out we'll call that one the "4th carb" since it was the last one I disassembled.
Naturally, the bowls came off first and only pictures can describe the mess that was waiting for me. Three out of the four carbs looked salvageable but the "4th carb" was a disaster. I can only assume that the bike was left sitting on its kickstand and the old gas (and other garbage) collected in the bowl thus creating these heinous stalactites. The candy like coating was brittle and everywhere. The float was frozen in time and all the jets were plugged solid.
Next the tops of the carbs came off and set aside. When I got to the infamous "4th carb", I discovered why the plunger was not moving with the other three. I can only guess that the gunk in the main jet caused the needle to stick and then somebody forced the throttle open thus bending the retainer inside the plunger. Not the end of the world thou, as that retainer can be bent back into place.
The jets were then removed and left to soak in a bath of "carb dip" for the next 2 days. In these tins, (purchased at the Dollar Store) I was able to organize the hardware according to which carb they came out of. Very handy, cheap and disposable.
After soaking in the carb dip, the jets seemed nice and clean however the idle jets were still plugged and needed some further assistance. I used the following tool to open them up and clean out any leftover gunk that the soak didn't take care of. It's just a piece of wire stripped down to one strand of copper. Once you get the wire thru the jet, I spin the jet on the wire while spraying either opening with carb cleaner or degreaser. Repeat until you can see light thru the jet.
Here's my cool new parts washer that I picked up from Harbor Freight. It's their newer 6.5 Gallon model. Right now I have 1 Gallon of Simple Green in it and that's it. It works great for the small stuff!
So back to our troublemaker, the infamous "4th carb". Against my better judgment, I decided to soak the entire carb (float and all) in the carb dip. I don't normally like to do this since the floats are plastic but I didn't see any other realistic way to remove the crispy candy coating that seemed to be plaguing this one carb.
Side note: I previously soaked the float bowls in the carb dip and it completely cleaned all the nastiness from the aluminum so I knew it would at least do SOMETHING.
I stripped the carb of as much as possible and into the dip it went. There it sat for a couple of hours. In the meantime, I stripped the other three carbs to the bare housing and prepped them to also be dipped. Once I felt the "4th carb" had been in the dip long enough, I took it out and tried to remove the float that was still pretty seized to the brass pin. Using a small punch and a hammer I carefully started to get the pin to move...
Side note: This technique may seem excessive for something as delicate as a carburetor however, the brass pins on all the other carbs wouldn't budge without some "coercion" also.
The brass pin seemed to be on its way out and I was just about to breathe a breath of fresh air when this happened...
It looks like the aluminum was just too corroded to take the force of the hammering and one of the ears that holds up the float broke off. Looking back, it probably would have been better to drill out the brass pin and replaced it with a new one later but I think this carb was doomed from the get-go. Oh well, hindsight is always 20-20. So the carbs are on hold now for a little while. I bought a damaged set of carbs cheap on ebay from a '75 and will eventually make a Frankenstein rack of carbs when the motor is done.
