New OEM petcock leaks

[Gottaride]

Installed yesterday. Re-pulled the tank just now to correct too tight choke cable and had a flood situation on my hands and thankfully cool engine. The petcock vacuum and all other tank connections had been removed. Petcock in the ON position, full tank of gas. Aside from a defective petcock what could cause this? The original? petcock worked fine so they will get swopped. Stumped and not happy. Good thing I installed the manual shutoff valve immediately downstream of the petcock.

[Gottaride]

Interesting discovery. With tank off of the bike while transferring gas to another container and only the petcock outlet nipple attached to clear hose all three petcock positions flowed high volumn. Attaching another clear hose to the petcock vacuum nipple I applied by mouth negative and then positive pressure a few times. Voila, after a couple of repeations flow would completely cease following negative pressure on the vacuum hose. Perhaps a brand new petcock sometimes requires a few neg /pos cycles to break in and operate correctly? Hummmm

[Mettler1]

Interesting discovery. With tank off of the bike while transferring gas to another container and only the petcock outlet nipple attached to clear hose all three petcock positions flowed high volumn. Attaching another clear hose to the petcock vacuum nipple I applied by mouth negative and then positive pressure a few times.     

  You did "what" to "what"    

[Vic Salisbury]

Installed yesterday. Re-pulled the tank just now to correct too tight choke cable and had a flood situation on my hands and thankfully cool engine. The petcock vacuum and all other tank connections had been removed. Petcock in the ON position, full tank of gas. Aside from a defective petcock what could cause this? The original? petcock worked fine so they will get swopped. Stumped and not happy. Good thing I installed the manual shutoff valve immediately downstream of the petcock.

Sometimes the spring on the vacumn diaphram can be stretched to add more "pressure" for a positive close. Of course make sure no grit or anything in the diaphram area?

[JDM]

Installed yesterday. Re-pulled the tank just now to correct too tight choke cable and had a flood situation on my hands and thankfully cool engine. The petcock vacuum and all other tank connections had been removed. Petcock in the ON position, full tank of gas. Aside from a defective petcock what could cause this? The original? petcock worked fine so they will get swopped. Stumped and not happy. Good thing I installed the manual shutoff valve immediately downstream of the petcock.

I have been doing some tests with a donated petcock from a 86 Connie with about 80,000 mi and the petcock off my 02 with about 75,000 mi on it. I am not finished with my tests but I can tell you if it were me I would get one of the Murphy petcock kits in a heartbeat. Once this valve starts leaking, it's takes almost no head pressure to unseat it and get it starting to drip. I stretched the spring out and did not see much improvement. I used a mini vac to unseat the valve. Some times the valve would re-seat and some times it would not. I also sprayed a small amount of WD-40 in to the outlet of the petcock and that did seem to improve it's seating ability, but not enough for me to trust it. It takes almost no back-pressure on the outlet to the petcock to fully open the valve. So, from what I have found so far, EVERYONE with the vacuum operated valve needs to make sure that the carb vent lines are clear and open with no restrictions. Also, there is a small weep hole designed into the body of the petcock that if it becomes clogged, then with a full fuel line and a hot engine, the heat soak could be enough to unseat the valve as the fuel expands between the petcocks and the carbs if not vented correctly. This is worth checking. I will post up more on this when I finish my tests.  PS SISF I sure need to talk to you. JD