Finally got the petcock working

I rebuilt the petcock last year using the instructions on this site but never got it working correctly. Fuel ran all the time on all settings. So, while painting the tank this year i decided to really look into the petcock operations, get to understand how it really works, and fix the problem. After disassembly it became evident the o-ring on the vacuum plunger that came with the rebuild kit I bought was too small or the plunger itself was too short and the o-ring was not contacting the orifice to shut off fuel.

With the vacuum port cover removed and the end of the plunger exposed, I placed the petcock in a vice and GENTLY compressed the plunger against the petcock body with the vice until I could maintain vacuum on the fuel discharge nipple. Re-assemble and apply vacuum to the vacuum nipple and ensure fuel will flow with light vacuum applied. It may take 2 or 3 disassemble, vice pressure, reassemble, to get it right. Just go very light on the vice pressure since you don't want to deform the plunger to much and have a permanently shut petcock.

jmd_forest

 

I think someone on here mentioned doing the same thing with a c-clamp and a socket -- I'll have to dig and see if I can find that post.

 

Damn, and here I thought I had contributed something useful.

jmd_forest

 

Meh -- GMTA. Anyway, I found one post; no mention of a c-clamp, but it does reference using a pair of sockets.

http://www.xjbikes.com/Forums/viewtopic/t=10069/

I had trouble with my leaky Max-X petcock; got a rebuild kit, kept leaking, tried the fix, broke the diaphragm plunger, put the old one back in, hasn't leaked since. Go fig.