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Mikuni Carburetor probs on an '85 FJ600 Mikuni Carburetor probs on an '85 FJ600
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Old 08-03-2008, 10:07 PM   #1 (permalink)
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Join Date: Aug 2008
Bike: FJ600
Posts: 4
Unhappy Mikuni Carburetor probs on an '85 FJ600
Hello everyone. I have a question about my bike. I have a 1985 Yamaha FJ600, I bought it off some people who had stored it 2 years with the same fuel in it. I pulled the carbs and cleaned them, checking all my gaskets, needles, seats, floats etc etc.
Put it all back together and I the bike flooded out. After some messing around with no luck, pulled the carbs again this time going over them with a fine tooth comb. (btw when I clean my carbs I do NOT use wire or anything harmful, only cleaner and low psi air) put them back in and the bike was still flooding out, now out the air box drain.
I found that the fuel cap was creating a lot of pressure in the tank so I took it off and it seemed to solve the problem. So I dismantled the fuel cap to check the vent hole, unplugged it and re-assembled it. Rode it for about 1 hr, and noticed that my cold idle was about 1200 rpm but after the hr of riding it was now about 3400 rpm. (I figured I must be getting too much fuel again) I shut it off and left it for 2 days.
Now I just went to start it today and fuel came GUSHING out the air box hose. (Now I know it's not the fuel cap) Shut it down and tore it all down. I noticed before that my tank, even with the valve on “On” or “res” still leaked fuel, with no vacuum hose on. So this time I pulled it apart and cleaned it, put it back on and it still leaked. (oh well)
Tore down the carbs again and spent about 2 hrs inspecting each needle jet and float. Everything seems to be perfect, even moving the float up and down there is 0 hesitation on the needle. Cleaned up the bike put the carbs back in hooked up all the hoses, put limited fuel in the tank, and when I went to start it, again fuel came gushing out the air box.
I'm looking into getting a fuel petcock rebuild kit, (because the flange that controls the vacuum valve IS kinda chewed and crappy and bothers me) but I know that this sounds like a float / needle problem to me. (BTW I'm going to try a small test tomorrow to see if I can find out what one(s) are in fact flooding out.)
So any ideas that may help?

Thanks in advance.

P.S. Sorry about the long story, but I thought I'd answer all obvious questions now.


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