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Carb test

Jim Reagan

CB750 Member
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Dracut MA
Hi, new to the site and hoping for some help with this many year project. Bought this '72 750 a few years back and have been fooling around with it for a bit having bought in 8 boxes with the engine torn down. Put that back together and now I am trying to determine if I have a "runner" or not which was the sage advice given me from a mechanic friend - before investing lots of $$. At the stage of setting up the carburetors and trying to determine if I can test this without completely connecting everything - plus it looks like a brass jet is missing from the bottom of the nearest carb. Basically, can i run gas from a hanging bottle through the fuel valve and into the two main hose that attach to the Y valve and see what happens? Once i buy a battery that is. Thanks for your time - all insights most appreciated.
 

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I use a seperate tank all the time to run bikes for tuning. Are you referring to the brass piece in the bottom of the float bowl? That is an overflow tube if the bowl gets over full. You should have rubber hose attached to each one and routed to a place behind the engine.
 
I use a plastic tank that I can hang on the ceiling above me. I have a valve in the line to turn it off.
 
what about trying to start it without the aircleaner / intake on and without the exhaust on? Like I said, i bought the bike in boxes and the previous owner told me that it had been blowing oil (confirmed by the inch of gunk behind the engine) but was running before he took it apart, but i have never run it. I have hooked it to my other bike's battery and cranked it over, just to see, but did not try to start it then.
 
Running without air cleaner is no problem. Running without exhaust is not a good idea. OK for a couple of seconds probably not going to hurt anything but be very care full because you would be suprised at how much of the flame you will get coming out of the head.
 
I hadn't even considered the flame factor...good thing i just bought a new fire extinguisher for the shop for just such a contingency. Seems that putting the half pipes on is a good idea and that's not too much trouble. Thank you all for your advice - if i'd known that CB750.com was out there sooner, i may already have had it running - hope springs eternal!
 
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