A few weeks ago I filled my tank and noticed the bike cutting out and coughing a bit for the next couple miles. Still rolling, I reached for the petcock thinking I might have forgotten to reset it. (Old habit from previous Honda, I know better but still did it) As soon as it was on prime it straightened up and when I corrected it at a stoplight about a mile or so later it stopped acting up. No further problem that tank but I added some sta-bil to the fuel just in case. Yesterday I had to switch to reserve just as I pulled into work, and filled up as soon as I got off and it did the same thing. Coughed like it was running out of gas until I switched to prime and corrected itself within a mile or two. Could this be the start of the infamous faulty petcock issue? My question to anyone that had that issue, how did yours start? Any other proactive suggestions? I've got an '04 with 7000 miles. Haven't pulled the vac. line off yet to look for gas. That might be my project for tomorrow.

Thanks

Dan

Dan,

The vac actuated petcock acts that way any time you run completely out of gas.   Mine sometime just flat refuses to do anything constructive when itself gets all constipated, vapor in the lines I suspect won't go through the mechanism as it makes a complete suction proof vapor lock and then has no engine vacuum to open the valve to fix the issue.

Solution for me is to pull off the road, kill the ignition switch (save up my battery juice for the stubborn crank up process) and put it in prime while it sits for a minute or 3 on the sidestand.   The gas in prime position has a chance to very slowly perk past the vapor lock and get some gas into the carb bowl over several minutes, getting just enough fuel to crank the engine.

Turn the switch back on and try a recrank.  Sometimes a touch of choke helps the recrank process, but once running the bike will suck some vacuum to open the valve and move a bit more fuel, ending the issue.

I got sick of this drill a while back and bought me a raptor petcock.

http://www.ronayers.com/browseparts.cfm?SearchString=5LP-24500-01-00&adv=5&kw...

Next time I take the tank off, this sucker goes in place and then all I have to do is remember to turn it to "off" every time I get off the bike.

Until then, I fill the bike up with gas every 100 miles (keep an eye on the odometer) when on a trip -- around home I fill it up every Saturday which does the same thing.

It isn't and I wouldn't -- if you have a good petcock that doesn't lose vac or leak or do the other malfunctions that it is known to do when the diaphram gets bad.  

If you were permitted to purchase the diaphram as a separate part instead of dropping big bucks for the whole unit, then we would have folks putting them in to fix their issues.  

But nobody has found a source for the diaphram as of now.

I would certainly rebuild the unit (if it could be made reliable) rather than going 100% mechanical which is a pain in the ass to keep up with.

Mine is still in liveable shape, which is why I haven't made a priority out of switching it out.   As long as I keep gas in the tank I have no issues and don't worry about it.

Every trip I take I wind up doing the drill at least once as I lose track of the miles and run it dry.   Then (while waiting for the prime position to trickle in enough gas to get it to start again) I vow to find the time to switch it out.

As a matter of fact, today I will switch out my vac hose again, just to be on the safe side for the upcoming trip.   I got several feet of the hose last time and have some left over.

My .02.
Obviousely, a vacuum hose will cause problems if it leaks.
It will also cause problems if old or weak.
It will collapse on itself when there is a large vacuum (high rpm, high speed).  That will close the diaphram, that will stop gas flowing, that will stop the engine as soon as the bowl runs dry.

As Southpaw did, anyone should be able to get it going again without stopping just by flipping it to prime with the bike rolling and in gear. Unless you get going so slow that it won't keep the engine turning over (and the back tire starts skidding instead!).

I don't know where this "vapor lock" condition is occuring.  Should have gravity fluid flow from tank to bowl and the float valve should be open which allows the air to escape from the bowl.  Certainly shouldn't take "a minute or 3" to get gas back to the jets again!

Question- does manipulating the petcock a lot hasten it's failure?  You know, always switching to reserve then filling up, changing jets and priming, etc.

Given -- I ran it out of gas before I noticed it beginning to stumble.

I can do that if I am at full highway speed as it is only a second or two of stumble before it is empty and tee totally dead.

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If the float bowl is empty ....

the engine won't run.  You can crank it, but you are just killing the battery.

If the engine won't run ....

the carb nipple/hose creates no suction on the diaphram.

If the there is no suction on the diaphram, there is no gas.

Prime on my bike works very slowly, why I dunno -- yes could be possibly gunked up some although I cleaned it with carb cleaner last time I had it off.   It could just take a bit of time to fill everything back up including the big fuel filter and the extra hosing to get to the carb bowl.

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Running the fuel line and the big fuel filter empty and having the bowl empty is a bad thing for my bike that takes me a couple of minutes to recover.   I have to wait to make sure I have gas in the carb bowl before cranking my battery endlessly trying to get it to start before the gas fills everything back up properly.

Being stranded with a dead battery sucks BIGTIME -- don't do that.  

Leave switch off, put petcock in prime and wait a minute or 3 for the gas to fill the fuel filter and make the trip to the float bowl.  Then turn it on, partial choke position and hit crank button once, it will try to start, push choke in all the way and hit it again.  Vrooommm.   Minimum drain to battery system.   Maximum number of attempts still available before draining battery.

You are correct.  The vacuum port is after the throttle plate, so it is manifold vacuum, and greatest at idle.  My bad.
That explains the fuel starve at high speed as well though.  Less vacuum, valve closes a bit, less gas when it is needed the most.
That's what I got once in a while.. embarrassing when in a group going down the highway.
I went to the Raptor petcock as well.