The reserve petcock setting feeds from a lower part of the tank where sediment can collect. Look in your tank. If you see any rust, you've probably located the source of your problem. The fuel screens and even an external filter can only protect from getting the larger particles into the carbs. Very fine particles can still get past them into the carb bowls. When the bike sits, these fine parcticles settle to the bottom and interlock with others to form larger particles. Run vibration dislodges these and they can block float valve closure, causing the carbs to over flow. Idle RPM doesn't use fuel faster than the over flow and the excess pours into the intake runners, upsetting mixtures, and causes uneven idling speeds. By the way, the tiny rust particles aren't an issue if the bike is run frequently and regularly. They just flow through the engine and normal fuel consumption keeps everything pretty clean. However, if your tank is heavily rusted inside, you will need a lot of regular fuel flow to keep the carb internals working correctly. These machines were made to be driven and not parked for months on end. I find the stock filters are quite adequate when proper care of the fuel tank is provided. But, if redundant filters please you, then go for it.
So, what to do now? Check the in-tank filter or the one on the petcock (whichever you have). Check for crud, clean it, and eliminate the source of the crud. Flush gas tank if neccessary. I've had good luck with the Kreem system on rusty tanks. But, I follow directions well. And, I allowed two weeks or more for the coating to cure (with forced air circulation) before I put fuel in the restored tank. I recommend flushing the carb fuel bowls. Your choice of method. On the CB550s the drain plug can be removed and carb cleaner in a spray can can be used (with the nozzle) to squirt into the drain hole and flush the bigger stuff out. Use your judgement and a catch tray. (Hmm, I wonder if you can trust a self proclaimed idiot's judgment... ;-) ) Anyway, if there is a LOT of crud coming out, then maybe taking off the bowls are warranted. This kind of thing can be addressed easily on the 550. But, I'm not sure of the precise procedure on the 74 750. Anyway, with the fuel supply providing clean fuel, 15 to 30 minutes on the freeway should complete the cleaning of the carbs, albeit at the cost of bug splatters elsewhere on machne and rider. On the other hand if your fuel system is clean and you still have these problems... Have you synched the carbs? Done all the rest of the tuneup items? Hope this helps, Lloyd SOHC4 #11 72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F, 78 750F Cook, Jason D PV2 BJACH-Ft Polk wrote: >Everything is ready except......I fixed my other problems and decided to tool around >on my 74 750K when I ran out of gas. I'm an idiot. Anyway, I put more gas in and now >my engine races and then it dies down and races and slows and races and slows. It did >this for a couple minuts and I wheeled it back to it's resting place to see what I >have to do now. I thought I did a pretty god job adjusting the float valves to 26mm >but it still overflows from time to time. I sprayed starter fluid all around the >boots a little while back testing for leaks and found none. Any ideas? > > > > >
