Petcock

[Vova]

So my bike was having some issues recently (http://gstwins.com/gsboard/index.php?topic=60131.msg692112#msg692112). Did a nice thorough service with an oil change, replaced spark plugs, and put a Shorai in to replace what I suspect was the stock battery (and not a minute too soon, when I tried to start it up the old battery did not crank at all, it was fresh off the tender too!).

So during the service the mechanic I was working with determined that the bike was in way too good condition for the carbs to be causing problems. Upon further discussion he recommended it could be an issue with the petcock. Well I think I just confirmed that. I ran great for a good hard hour on reserve, swap to on and within about a minute starvation and start to basically run out of gas, swap back to reserve no problem. Did that a few times to confirm. And yes, I have a full tank of gas  .

Question 1: I cannot find a breakdown of the petcock in my service manual. Is this something I can take apart and clean? He suggested I look at the diagphram as the culprit.

Question 2: Does the reserve line bypass anything in the petcock, why would reserve run fine while "on" is resulting in starvation and shutdown.

Question 3: It looks like the pengel gravity is a good upgrade anyway, however it looks like this would be difficult to reach to swap to reserve and even to turn off after a ride. Is this a problem?

[adidasguy]

Stay stock.

Are you sure reserve or prime? Both take gas from the reserve fuel line.  Remember that PRIME bypasses the vacuum. PRIME and RES are in different positions on the 89-00 petcock and the 2001+ petcock.

Most common problem if works on reserve and not ON is pinched main fuel line from the tank.
If PRIME and not ON or RES then check the vacuum line to the petcock. Easier to replace it if it is bad. Like any part, the rubber can wear out and get stiff. Stay stock. It works.

Anyone with a petcock problem gets very vocal about it and preaches that vacuum petcocks are horrible. If I did the same on a different part, you'd be hearing that fork seals are garbage and forks should be welded tight so you don't have fork oil leaks anymore. I've had more fork seals go bad than petcocks out of 4 bikes (fork seals: 2;   petcocks: zero). I'm not sure why people are so vocal about a petcock and not about all the other parts we replace far more often. maybe because you can ride with oil and fork leaks. You can't ride if no fuel flow. There is PRIME - and switching to PRIME is that any different than an on/off petcock? you have to flip the lever. So? Wouldn't that really be the same thing?

Change to something else if you want - it is your bike - it is always an option.

I wouldn't consider a pengle an upgrade. It is a change or a side-grade. You have problems reaching it then remembering to turn it on and off. If you race it probably makes sense to have free flowing gas.

Like I said, if you have to switch the gas on and off, is that any different that switching to PRIME when you turn the bike on and to either ON or RES when turning it off? Seems about the same to me and costs you zero dollars for the same inconvenience of remembering to flip the fuel valve.

[Vova]

Hmmm seems unlikely it is a pinched line as the problem started out of nowhere. Then after the service it was still a problem and we did not notice any pinches or such worn into the line. Just seems unlikely the line worked its way into a pinch and then happened to get placed there the same way when putting back together.

That being said if the reserve line does not bypass anything there is no other reasonable explanation. Not looking forward to having to remove the tank to look again but...

I hate these problems because it is ruining the faith in my bike, worried to ride when I need to be somewhere, which relegates me to weekend warriordom presently 

[adidasguy]

There is always the PRIME setting as it bypasses the vacuum.

A tube, if in a bend, can go into a sharp bend and pinch itself off if it gets warm or softened in any way. I think you've seen  that happen with a garden hose. "WTF? No water! Oh, it bent and pinched itself off." Straighten out the hose and water comes out again. Not saying that is it, but once you get a pinched line it is hard to un-pinch.

Do the test with a clamp & pull the like off of the petcock and see if gas does flow out of the main fuel line. Don't have to take the tank off to do that.

[mcg2000]

From reading what you guys have so far, I would check to see if the main fuel line from the tank to the petcock is clogged in any way. Take the tank off the bike (leave the two rubber hoses on) with the valve off so fuel doesn't pour everywhere, then plug your reserve line (since that one works). Then open up your tank valve and see if you have any flow out of the main line (with enough fuel in the tank to run on "on" of course).

As for the petcock, I've taken mine apart recently in a "no fuel" situation.  Turns out it's a pretty simple set up, and you can take it apart safely as long as you pay attention to how it will go back together. But I don't think it will help you at all. It was just a learning experience for me and caused a "click" in my head that made me realize an obvious "no fuel" cause.... I didn't have enough fuel to run in "on" when I thought I did, haha!

[adidasguy]

I posted this in another thread on basically the same topic. You can test the lines without removing the tank.

Get one of those surgical clamps. Clamp the main fuel line before the petcock. Pull off the fuel line from the petcock. Now, with a glass or fuel proof cup  to catch the fuel, unclamp the hose and see if fuel gushes out. If it does - petcock problem or vacuum line problem. If not - pinched hose. Be careful not to jar the hose much. If pinched, you might un-pinch it and not know it was pinched.

You can check the output of the petcock, too.
Attach a fuel hose to it into a container.
Attach a hose to the vacuum port of the petcock.
Suck slightly and see if fuel comes out in the ON and RES positions. Fuel will flow freely in the PRIME position.

As an FYI: The clamps on the reserve line: use that to drain the tank! No need to remove lines from the tank or turn off the tank. I did that to change the tank petcock on Phenix (It was OK- just a defective washer on the bolt holding it). Before taking off clamp, I stick a vacuum cap thingy in the end to plug it up. Then did same with main fuel line. Then took off tank taking the fuel lines with it.

Putting back on: clamp the end of the hose. Remove plug. Attach to petcock. Remove clamp. Repeat for other hose. Hint: You can remove the plug and clamp to be sure fuel is coming out of the fuel line and it is not kinked or pinched anywhere. Then clamp and attach to petcock.

Note to self: buy a few more surgical clamps. They are really handy on fuel lines!