Finally got some time to get back to the surprisingly clean carbs from the CB900. I went through the various air and fuel passage ways with some carb cleaner and all the pathways seem pretty clear. Piece by peice I started reconstructing the carbs replacing all original bolts with stainless socket button-head screws and also replacing all O-rings, diaphragms, and gaskets. As this bike is already running with an aftermarket exhaust (and I plan to run without the airbox initially) I also applied the DynoJet Stage 3 (which included a new needle and larger main jet set to DJ130 from stock 105). The Stage 3 also calls for the air mixture screw to be backed out 3.5 turns (instead of the stock 2.5); and that’s where my problems started.
I already noted that there were a number of problems with carb 4 on this bike, especially with the air mixture screw. While attempting to install the air mixture screw I found that the carb body is stripped (looks like someone was trying to dig out the air mixture screw at some point). The result is that I can’t install the air mixture screw anywhere near the correct back-off.
In an attempt to fix the problem, I’ve filled the upper part of the hole with JB Weld and am letting it set for the next 24 hours. Hopefully it’ll harden enough that I can drill out and thread the hole and start moving forward again. If not, I’ll probably look for a replacement body on Ebay.
While waiting for the JB Weld to set, I went ahead and put the remaining 3 carbs togetther. I was able to put carb 1 and 2 back together.