I finally got around to putting my 1986 VFR750 back on the road this summer after 5 years in storage. I replaced the fuel pump with a Mr Gasket 42s and took the carbs off and cleaned all the gunk out of the jets and float bowls. It ran well except it wouldn't idle with the choke on but once warmed up it ran like a champ! After putting a couple hundred miles on it I went out last weekend and had it die on me. After parking it for the night I found gas under carbs but couldn't figure out where it came from so I took the air box off to take a look. I got it running and was trying to find the leak when we revved it up and a big glug of oil and gas blew out of the breather tube! Pulling out the dipstick there was gassy oil (or oily gas?) all the way to the top of the dipstick hole. Obviously gas has somehow been leaking through the carbs into the case. First thought was that one of the float valves was leaking but then gas would be leaking out of the overflow tube wouldn't it? After pulling the floatbowls off and checking the float valves by sucking on the seat to confirm that needle was seating I put everything back together and hooked them up to the pump. After the pump ran long enough to fill the floatbowls I noticed gas leaking out of one of the carbs, basically raw gas would have been leaking into the cylinder head if the carbs had been connected. When I pulled the plug from that cylinder it was black like it had been running rich. Any have an idea what's going on? Could the new pump be somehow overpressurinzing the carbs and forcing gas through the jets? If the float valves were leaking wouldn't they leak out of the overflow tube? I'm a little scared of the damage I already did running the engine with a bunch of gas in it and don't want to change all the all the oil to have it. I'd appreciate any thoughts or theories.
The 42s pump is rated at 4 PSI. If the needles and seats are in good condition, this pressure should not overcome them. Could be floats sticking, but most likely needles and seats need replacing.
Pressure from stock pump is 3 psi, but Creaky's right, replace your float needle on that one faulty cylinder or all 4. Vent tubes usually drip from overflowing but not necessarily cuz alot of excess fuel just bubbles up through the main jet outlet tube, and the vent lines are much higher. After sitting 5 years the float needles can grow oxide chrystals that cause jamming, so a careful going-over with green scotchbrite might help. To clean the seats i put some gritty kitchen cleanser on the tip of a wet Q-tip and twist it around, rinsing after.
