F'd by a petcock!?

So, long long story short, last year I was fighting some carb issues. It seemed rich at 3/4 throttle. Found out my fuel levels were a bit off. Adjusted them to spec and then proceeded to fight with an odd lean issue. Starting the bike was fine as was riding around with the choke some. But, I noticed that as it warmed up, I could take the choke off, but it would FALL on its face from a stop. I fought it for a few weeks, looking at my pilots, air leaks, exhaust leaks - everything. As the weather turned to fall and winter, I kinda thought I had finally got it dialed it.

When winterizing the bike, I noticed a carb weeping some. I already knew the needle in that carb was at end of life. So, the past few days I spent swaping in some new needles and seats and getting the level dialed in. For shitz and grinz I decided to throw the battery in and fire the bike up. She popped right off and I let it idle for a while in the garage. It was a little rough, but hey, its WI and its cold in the garage.

As it was idling, I noticed the little clear fuel filter looked to not be flowing. It looked halfish full. I threw the petcock to PRI and a GUSH of fuel came down for a good 5-10 sec and I could tell the idle of the bike picked up some and level out a bit....Now, this doesn't make sense to me. In the ON position, the fuel comes through the little straw higher in the tank and through the valve, which should provide almost as much fuel as the PRI position, right?

Anyway, I think I was starving my bike of fuel some - Either the petcock needs rebuilding, theres crap in the vacuum line or maybe something plugging the ON circuit in the valve.... Kinda lines up with my lean issues last summer - maybe it was passing some fuel, but not enough to keep up and it was a slow leaning of the mixture.

It wasn't opening all the way.
Time to rebuild it before spring sets in.
Steve

Sounds like the typical saga of a vacuum petcock that's either got problems due to age internally with the diaphragm or something sticking or a vacuum leak in the feed to it so it's not opening properly. I'm not a fan of vacuum petcocks personally, I don't know if you can get a rebuild kit for yours or whether a manual petcock replacement like a Pingel would be the best option, just remember to cap off the vacuum point on the carb or where ever they draw the vacuum from to work the petcock, if you take the manual petcock route.

They're a good idea but another thing to go wrong.
Steve

Anything you do should start with emptying the tank and pulling the petcock out. Take a look at the screen filter and make sure it's not clogged. Probably not clogged but the run position circuit is partially clogged. I would take it apart and soak the body in vinegar over night and do a final clean up with tooth brush and carb/brake cleaner. Careful not to tear the diaphragms when taking them apart. Be gentle and patient take your time. Once clean you can assemble the petcock but leave the selector off (not installed) so you can see the internal valve. If you have a vacuum pump like a Mighty Vac you can apply about 3 to 5 inches of vacuum to the vacuum port and see the valve move. Do this a couple of times to make sure it's not sticking. At the same time watch your vacuum gauge and make sure it holds vacuum and doesn't bled off. You did lube the o-ring on the valve with Vaseline prior to re-assembly right?

After this it should work OK. If not then you can pursue a replacement.

I forgot to mention. Once you get the petcock apart and the selector off, you'll see that round gasket with 5 holes in it. If it doesn't fall out just leave it alone and into the vinegar with the rest. If it's stuck, as often is, just leave it alone. You'll probably tear it trying to remove it. while only about $5 on eBay, you don't to add to the aggravation. The object is to fix the petcock, not fix it until it's broken!

:lol: :woohoo:

swest wrote: They're a good idea but another thing to go wrong.
Steve

While sort of a good idea, I always feel they were a feature for the less informed who couldn't be relied on to turn a petcock off an on, which had been the norm for the previous 50 years or so of motorcycling. Like any additional complication to a basic idea they were very convenient when everything was new. I remember liking the idea at the time. However 30 plus years later with old parts etc. I'm not so keen on the idea as they are far less likely to be reliable and my biggest concern would be creating a situation with inadequate fuel flow that could lead to internal motor damage as things get too hot with partial fuel starvation when riding hard.

Agreed on them being another thing to go wrong. Usually I replaced the damn thing almost yearly as it would fail open (like permanent PRI) or it would piss out all over my leg as I rode... Never failed this way.

I run an '83 GPz750 petcock that was a bolt on and it has larger passage's
and flow's a lot more than the stock KZ650 petcock.

apbling wrote: Agreed on them being another thing to go wrong. Usually I replaced the damn thing almost yearly as it would fail open (like permanent PRI) or it would piss out all over my leg as I rode... Never failed this way.

To me it would be tempting to get something like a Pingel petcock and put the original on the shelf in case I ever needed it for the sake of originality while in the mean time enjoying some sort of reliability and peace of mind. It didn't seem a problem back in the day, but now when I'm not riding everyday etc. and perhaps with modern fuels, I seem to experience more frequent float issues with my various rides and don't want to fill my crankcase with gasoline, or smell gasoline in my garage if it can be avoided, so I'm becoming more of an "off means off" kind of guy.

Technically, couldn't one modify the petcock and plug the on position off so it's actually an "off" and use prime when you want to ride?

Wouldn't require welding or any mods to the tank.