Here goes...
I am the very happy new owner of a 1975 CB750 K5 that is in decidedly good condition for it's semi-advanced age. It does however have a few "personality traits" that need a little attention (shocking I know). I am fairly mechanically inclined and plan to do most or all of the work myself. I have the Haynes, Clymer, and factory manuals to guide me as well as you guys :-). Any and all responses to the following questions are appreciated.
First off, congrats! You've done the right things by getting the manuals before you dive in.
1. When the headlight is on should the front orange lights be on but not the rear orange lights? The blinkers work fine but the front 2 lights are always on with the headlight. Also, the "Turn" gauge light is lit solid when the headlight is on and does flash when the turn signals are on. Is this normal?
The front two turn signals have dual filament bulbs and the dimmer of the two are supposed to come on with the headlight and serve as running lights. The rear ones only flash. The turn indicator on the handlebars should only flash when the turn signals are switched on. If it's on when the headlight is on, something's not right.... (If everything was in order, there is a beeper that should sound when the signals are on. This was to remind you to shut them off. It's annoying and most folks disconnected them or tore them out.)
2. I found the main fuse wrapped in tinfoil and a 14a fuse in the 7a headlight fuse spot. Amazingly everything works fine with the proper fuses in place but I noticed that the headlight works with or without a fuse in the middle holder. Gotta think this is wrong.....
Get new (and correct) fuses before you do anything else. If memory serves, the main is 15A, headlight 7A and tail light 5A. You will likely have to look for shorter fuses as the standard automotive ones are a bit long. While you're at it, clean the fuse clips as corrosion can cause them to heat up and potentially melt the fusebox...
3. The bike starts and runs great but bogs down if the throttle is really openned up. It eventually clears out and can get from 55-75mph but something is not right for sure. I'm guessing carbs right?
Maybe, but how do the plugs look? Are the carbs sync'd? How does the airfilter look? Go over all the tune-up items before you start to tear into the carbs... If the carbs do indeed need tweaking, the jet needles likely need adjustment. What size jets are in there now? Is the rest of the induction system stock? (I know, lots of questions, but required info to sort things out)
4. Should I leave the 4-1 exhaust or go to a 4-4? All the pics I have seen of this model have 4-4 pipes. Has mine been changed? Is there and advantage to either? My muffler has a big dent in it so I'm not oppossed to changing the whole exhaust.
It's up to you. If you want the bike to be perfectly stock, go with the original HMC-341 4-into-4 pipes and be prepared to plunk down big bucks if you want new replacements. Some like the sound of the 4-to-1 better, and in some cases it can give slightly better performance, but as to how much improvement, I can't say....
5. Is there any kind of conversion for changing to a wider rear tire with disc brakes? Am I being a non-purest by asking this question?
Again, it's up to you. The rear drum on these bikes was very good and can easily lock the rear wheel. The later F-model 750's had a rear disc and you could probably lace up a Harley 16 inch wheel to accomodate a bigger tire. Another popular mod is to convert the front to a dual disc setup. Many have done this and there are outlines on how to perform the conversion. This might be an easier route to take...
