Petcock buggered?

[shpielers]

Hey guys.
This is long, trying to be as detailed as possible.

Riding home from work Saturday my bike ('06 600) started getting very boggy and struggled to make any power, had a fun time getting the rest of the way home. If I tried accelerating, almost nothing happened. Bike wanted to stall whenever the clutch was pulled in. Bike died as I hit the driveway - talk about good timing!

I figured it's one of several things:
-bike was overheating (it was only 90 degrees, was on the bike for about an hour and a half, almost all super slab. I've gone further while riding harder for longer in higher temps and the bike was fine, but I was due for an oil change - maybe old thin oil wasn't doing the trick anymore)
-fuel delivery issue (kinked line, clogged filter, carb issue etc)
-electrical (plug wires arching, loose connection, bad plug)

Pulled the bike into the garage, and sprayed water on the headers to see if that might help point me in the right direction. Cylinder 3 was a fair bit cooler than the others.

Sunday was a planned maintenance day, so again, good timing. Did a valve adjustment, clutch adjustment, chain adjustment, oil change, and (finally) drilled out the A/F plugs and moved the screws to 2.5 turns out. (They ranged from 1.5 to 2.25). Valves were fine, only #4 exhaust was a little tight but still within spec. Verified #3 was sparking. Didn't see anything unusual while I was mucking around in there - wires looked fine, plugs all in good condition (due for a change in another 3k miles), vacuum hoses all good, fuel filter not clogged. Started the bike up so it could get warm for carb syncing and synced. Let the bike cool off again, and started it up again. #3 is now not running cooler, and all 4 seem to heat up at the same rate.

Geared up and ride it around the block - ran fine for about 1/4 mile then the same boggyness as from Saturday returned. Got home, did another spray test, all pipes seem to be ~ the same temp. So doesn't seem isolated to any 1 cylinder.

Hopped back on, switched petcock to prime. 0 bogging. Really nice throttle response. Switch to run, bogs. Back to prime, it's fine. Switch to reserve, bogs. Switch back to prime, issue clears up.

So it's definitely related to fuel delivery somehow. Double checked the line from carb 4 to the petcock that supplies vacuum - it's fine. Replaced it anyways with something a little thicker. If it was kinking/pinching figured that would help. Hop on, repeat test, still fine in prime, still shitty in run/res.
Open gas cap and repeat test thinking the tank vent might be clogged. Nope, same results. Removed tank and hooked up some tubing. Applying vacuum makes fuel flow great in both run and res, flows at the same rate as in prime.
Disassembled the petcock thinking maybe it's dirty/clogged. The screen is fine, petcock looked really clean. Oring was fine. Vent hole to atmosphere is clear of debris. Put everything back together, same issue. Verified line from carb 4 to petcock is actually pulling a vacuum.

Bike basically won't run unless it's on prime.

So after all that if you've managed to actually read this far my question: since applying a vacuum makes fuel flow, wtf else besides something in the petcock could this be? Time to rebuild it? Again, everything looked ok...
I'm going to order a rebuild kit for it, worst case scenario, it's got 64000 miles in it - won't hurt anything.
Can anyone think of something else that might cause this, or something specific to look at in the petcock? Me and my not so advanced sense of mechanical troubleshooting are pretty sure it's something in the petcock, but I could be wrong. Any/all ideas appreciated.
Thanks guys!

[92xjunker]

Crap clogging the passage, worn Diaphragm ei: being stiff. Vac hole clogged, dislocated spring. I'd go with stiff diaphragm as it does function in prime and the spring is used as well. Could be a vac issue also.

[shpielers]

Rebuild kit ordered.

Nothing in the passages, vac hole is good, spring is in the right location. Hoping it's the diaphragms just deciding it was time to quit.

Really shouldn't be a vacuum issue, there is vacuum on the line. Enough to successfully sync carbs and feel it at idle at any rate. When I had it off the bike, sucking on a hose attached to the vac port just a teeny bit was enough to get it to flow.

One thing I never did was have the vac line on the petcock while hooked up the the tank with the bike running and visually verifying flow with a running engine. I'll try that in the morning. Don't expect it to provide any new information, but worth a shot.

[Kreylyn]

If the diaphragm has a small hole in it, that could reduce the fuel flow some. Reduced fuel flow can give you a situation where the refill isn't as fast as the use... so it bogs when running, but you see fuel flowing when it's not and testing.


For that, I normally suggest when your doing the vacuum applied test with the tank off the bike, that you crimp the line with suction applied. Crimping the line should hold the vacuum and fuel keep flowing for at least a min. If you see it just start to dwindle down and stop, then it's a hole leaking in the diaphragm that is allowing the suction/vacuum to be decreased. That in turn reduces how much the bike vacuum will open the plunger, and of course that means reduced fuel flow.


If your applying suction to the hose for the test, that suction amount is going to be a lot more than what the bike applies. You can tell the difference there just by using your finger to cover the holes, and compare between them both when the bike is running.


Krey

[shpielers]

I was wondering if it might slowly be losing vacuum somehow, never thought to try testing it that way. Thanks, I'll give that a try too!

[elsueco]

I just went through the same thing where my bike wouldn't run on Run, but would on Prime and Res. Turned out to be the petcock, and a rebuild did the trick.

Some of the orings were chewed up, but didn't look like they would have blocked anything. The diaphragm looked in good shape for being around 20 years old. I couldn't see anything obviously wrong like the clogged Run hole I had expected.

I did find some black goo behind the nipple where the vacuum hose attaches. Since there's a pressed in plastic screen behind the nipple, the goo only loosened in my chemical bath. But, I was able to spray it out using a lot of carb cleaner.

I'm not sure exactly what was wrong with the petcock. If the goo was blocking the vacuum, that should have affected both Run and Reserve. If there was a chunk of something obstructing the Run hole, it was gone by the time I took the petcock apart. Regardless, I now have fuel that flows like it should.

I'm not sure what I did wrong, but when I popped the knob back on, it was really hard to turn between positions. I ended up taking it off again and lubing it. Now it turns nice and smooth. Oh, and also screw the two halves together tightly around the diaphragm. Ask me how I know the importance of this...

[raidinmd]

sorry to slightly hijack, but when my gas gauge reaches the red mark my bike will start to bog down and lose power (especially on highway), the tone of the exhaust drops too and i'm not sure what would be the cause of that, i know its low and i turn it to reserve at that point but i only use about 3 gallons at the point and my tank hold 5.2, should it be doing that?

[elsueco]

Yes, sounds like you're hitting reserve. Kats are pretty gentle about hitting reserve, you get a minute or so of sluggish performance before it'll die on you. My cruiser just coughs three times then dies when it hits reserve. PITA.

My reserve and fuel gauge are also fairly well in sync that usually when the needle hits red, it's time to turn on Res.

Your tank THEORETICALLY holds 5.2 gallons. I'm sure this is only ever achieved by Japanese engineers under laboratory conditions. Or else their reserve tank estimate is way off.

[shpielers]

Well, doesn't seem to be slowly loosing vacuum. Held a steady rate of flow for a full minute. Also verified that carb #4 is pulling vacuum.
Guess I'm just going to have to wait for that rebuild kit to come in.

Rainmd - I always leave mine on reserve and just go by the trip meter. But I've seen several people on here say that 3 gallons is right around where they hit reserve.

[raidinmd]

thanks a lot, hope you get your bike on the road again soon, it's a terrible thing to drive on four wheels when you don't have to

[shpielers]

Totally agree. That's why I'm still riding. 100 mile round trip commute in a cage? No thanks.
My carbs are in good shape so I'm not worries about running it in prime for a couple days till that rebuild kit comes in. I'm still switching it to run when I park the bike just in case.