Son wanted motorcycle. I've been riding for 23 years. Mostly old stuff, 80 Yamaha SR250 (don't laugh, I bought it for $85). '75 Kawasaki Z1900, '95 Virago 1100 and currently a '72 CB500K1 (mostly restored).
He found an '87 CBR600F on craigslist, listed for $500, not running (paid $400). Pics looked good though it had been customized. For that money I suggested he jump on it. Phone tag ensued. He couldn't go see it, sent me with cash. I offered $400, deal done. We went back with the mini van and it fit!! Last night we tinkered, finally got it to fire but realized the pump wasn't running. Hot wired it, ran great, too great. Wow. I'm not used to bikes like this!

Question;
I'm foggy on the whole fuel pump power circuit. Studied the diagrams but the Fuel Cut Relay will not supply power to the pump, there's power going into it. I pronounced it bad (for now) and rigged a toggle switch to the pump for temporary testing.
Anyone know how this circuit is supposed to operate? This bike has been heavily hacked so who knows what the wiring is doing. Supposedly PO used it last season, couldn't get it to run this year and sold it off. I assume it was wired correctly since he said he ran it. I assume the relay simply died (do they do that?) I'd like to test the rest of circuit but I don't get it, it seems wired (via Yellow/blue wire) to the start unit, a coil and the tach (which I assume tells the relay it's okay to run the pump as the bike is functioning) it also is wired via a black wire through the fuse block and the handle bar switch, the start button I assume? So the relay gets power from the start button, to run the pump, then once the bike is running (and start button released) the power comes from the Yellow/blue via the spark unit, so should the engine stop running for any reason (key off or accident) the pump circuit is interrupted and you don't pump gas on your wreck?
I think I just explained it myself, no?
I swear I was getting voltage at the relay from both yellow/blue AND black when the key was OFF! If so, well the wiring is seriously messed up. I will investigate that further. Bike is pretty cool. Hacked up, but "street fighter" it is.

 

First off let me say welcome to the forum. That is a really nice looking bike you got there, and for $400 too... great find.

So the fuel cut relay is basically what top the fuel pump from running when the engines off. Basically when the start button is pressed, the pump is powered. When the tach is showing the engine is running, the pump is powered. The relay is likely bad, but you should be able to pick up another one quite easily - they used similar parts for many models.

 

Okay, I'll probably just replace with a standard relay (likely have some) rather than spring for an overpriced one. Might loose pump squirt for a second during start but I kinda doubt that's critical.