When to replace cover set on petcock?

[MarcusS]

I have a 98 Std that I pickedup last fall with 19.5K miles and have put about 5K miles on it. A couple of weeks ago, I filled up the bike at a gas station at the bottom of a long entrance ramp up to an elelvated highway. It was a quick fill where I did not even take off my gloves.  When the key was back in the ignition I fired it up and hit the ramp hard. As soon as I was in second I rolled back the trottel to enjoy the g-force. I went thru the gears as normal but when  got in 4th the g's stopped at 4000RPM?  I seamed to run out of gas after about 6 seconds of hard trottle.  I was allready going over the speed limit and backed off and she ran fine. I have put hundreds of miles on her sense then and have not experianced the loss of power. Have not done any more up hill drag races. How long can a bike run under full throttle with no vacume before it starves?

I have a cover set that I purchased for my personal parts stock but think mine is working. I drew a vacume on the line going to the cover set last night and mine is not leaking. It held vacume well.

I do not want to replace something that is working. 

I have two thoughts.  Unlike some other things, rubber gets harder with age. When under full throttle there is little if any vacume to hold the valve open.  Does it take time for the cover set to fully open and stabilize when you start a bike? I assume that older covers require more vacume to hold them open.  I went from off to full throttle in about 6 seconds  when I hit the ramp where I experianced the power loss. Could it have been a water slug in the new gas?

I replaced the tires due to age. Should I go ahead and replace the cover set just because I can?
I don't want to be replaced just cause Im old. I think I will put the new kit in my bag and just carry it for few years in case my diaphram lets go or gets a hole. As long as you have a spare part on the bike the need never arrizes. Its the parts you don't have that break.

[Chrisj CMA]

two things.  The power loss you describe (to me anyway) sounds more like the rev limiter.  Hitting the rev limiter when you arent expecting it could feel like  fuel isue.

Second.  By the time an OEM pecock starts messing up and needs that cover set.....you might as well replace the whole thing with a good fuel valve.  That factory one is the worst piece on a stock Valkyrie and IMHO never worth rebuilding

[Chrisj CMA]

PS...Since you did ask directly........there is a weep hole in the vacuum side of the valve.  There will usually be an intermittent drip out of that little hole if there is a tear in the diaphram.  The rest of the petcock can appear to be functioning normally but wont for long if its leaking.

[Michvalk]

Running out of fuel can be caused by a leak in the intake that has the vacuum line for the petcock. The seals at the bottom of the intakes can dry up and leak. There also can be a crack in the vacuum line to the petcock. Also want to check all the clamps on the carbs since your gonna be in there anyway. Just some Ideas

[MarcusS]

I synked the cabs not long ago and #6 was in line. The hose from #6 to the cover valve is new. I looked at the tach when it cut out and it was around 4K . I have hit the rev limiter several times and it sounds and feels odd when the ignition cuts out. It was fuel starvation or bad gas. I had just filled up so any garbage in the tank could have gotten stird up. Gas station did look questionable. Fuel milage on that tank was also poor. Went to reserve at 105. I looked at the cover set assembly diagrams and there are two diaphrams. one is dry ( Vacume) and one is wet ( Fuel). The vent is in the dead space between the diaphrams. Bad dry diaphram and it should suck air. Bad wet diaphram and it leaks fuel when the valve is open. I may put a small bandaid over the vent to see if it gets wet. Ive put 300 miles on the bike sense the odd power loss without it missing any power. I can crank wrenches every night of the week to prevent loss of a long ride on a weekend but replacing good parts is not one  of my plans.

[Willow]

If it only happened once it sounds like you may have gotten some bad gas, maybe even water in the gasoline.

If you can reproduce it it could be a failing petcock, but also could be any restriction along the line of the fuel flow, including the screen in the tank and the lines to the carbs.

Four thousand RPM is way too low to be anywhere near the rev limiter.

[MarcusS]

Last night I did more investigation in my garage. I rand my hand under the valve and it came out smelling like gas. Something an't right. I took a piece of paper towel and bloted the vent and found a small damp spot.  I put a vacume pump, that I use to flush the brake lines, on the #6 hose and watched the vent. Could not make it leak and the vacume held. This morning at 5:30 I ran my hand back under the valve and it was damp again. Not dripping, just damp. Something is leaking and justifies a tear down.

[Daniel Meyer]

Last night I did more investigation in my garage. I rand my hand under the valve and it came out smelling like gas. Something an't right. I took a piece of paper towel and bloted the vent and found a small damp spot.  I put a vacume pump, that I use to flush the brake lines, on the #6 hose and watched the vent. Could not make it leak and the vacume held. This morning at 5:30 I ran my hand back under the valve and it was damp again. Not dripping, just damp. Something is leaking and justifies a tear down.

Sounds like the vac side of the diaphragm is okay and the fuel one is bad/worn (there are two, linked together).

No amount of fuel leakage is acceptable.

Replace the cover-set (including the cover!)