cb750 doing basically everything wrong

[wibblewobble]

Guys I have a whole host of problems and beseech your wisdom. As I said I cannot get my cb to just run reliably. I will preface this by saying this is the first bike i have ever owned or worked on. The only thing I know to do is describe my situation in complete detail.

But my first question is, if a carb casting is broken/cracked, is it trash or can it be repaired? I have a good feeling this is the root of some if not all my problems. When I got my bike (not running of course) the main jet holder extrusions in two carbs were cracked and covered with Im assuming jb weld, quick steel ect.
-If this is a "well theres your problem" thing than please tell me.
And now my details:
1974 Cb750
stock airbox, stock style air filter, 4-1 mac exhaust, stock size and notch position jets-as far as I can tell- (rebuild kit jets though), new boots between box, carbs, and engine, new points and condensors new plugs. new gaskets and o rings in carbs, new petcock and inline filter

What its doing: The result of the last assembly was this: it ran well, idled well and revved well, but idle would surge and hang at high idle. I can't find any air leaks! I thought I would keep tuning carbs and syncing until I sorted it out. Cut to a week later (after having touched absolutely nothing) bike won't run like it did, and revvs all over the place, it idles well but exhaust pops, no throttle repsonse until it hits higher rpm, and without warning it revs to 7000 and sound like it wants to keep going but I don't let it go further, I shut it down. What could have happened in a week of sitting?! The only way I can describe the exhaust smell is like that of a weed eater, rich to me.

What I've done first:
timing-set with multimeter according to manual procedure, (carbs removed, rebuilt, cleaned 3 times bench synced and synced with vacumm gauges at 3k and 1200 rpm to the best of my ability when it ran well enough) checked simple things like sticking cables/slides ect. I have the tank off to the side so I can see. float level set 26mm,  


I am beyond baffled.

[TOOLS1]

It really sounds like you have a vacuum leak. It may even be in the carb housings themselves since you describe them in bad shape. However I have repaired cracked jet housings with JB Weld, and a .45 shell casing. Just cut the end off the shell casing, and JB Weld it over the jet holder.
TOOLS