Rebuilt petcock, but get a trickle or no flow

Using Fitz's guide http://xjbikes.com/Forums/viewtopic/t=25058.html on rebuilding the sender, as a follow-along, I rebuilt my unit (82 XJ750 Maxim), but am still getting the same behavior as prior to a rebuild.

I replaced the plastic disc "valve", not the sender block. The rubber diaphragm, and the bakelite disc for the vacuum port -- as placed behind the brass removable nipple. Also replaced the in-tank filter and the selector o-ring - not the wave washer.

I polished up all mating surfaces, smoothed down all flat metal sides - I even polished up the tank-side mating surface to ensure smooth sealing.

All of that, and the sender.....doesn't send! So the bike wont start.

I'm starting to love this bike like a bad marriage.

 

did you test it to make sure that fuel flows freely when it is on PRI? Do you have a fuel filter?

How did you determine that the pet rooster had issues delivering fuel to the carbs?

 

ON, PRI, and RES dont flow much if any fuel. I can tell the flow rate from the inline filter I have - new last season (installed following the arrows in the correct direction). When using the starter, I can see the filter "pulsing" with gas in the gold-colored element - for lack of a better description.

I know its having problems, because an external tank will fill up the filter without problem. The only indicator since the fuel lines aren't transparent.

 

Take the selector valve out and check to be sure that you put the rubber selector gasket in correctly. If the holes aren't in the right place they will block the fuel passages.

 

I think you mean the rubber diaphram?

I'll disassemble and upload some photos for it. I didn't think there was anything particular about it besides getting the nipple-end to sit on the corresponding petcock side (passageway heading towards selector lever).

 

Why not just buy a new pet? They are not that expensive and if it is a problem with the pet then it will be solved.

 

Nope. I'm talking about the seal inside the selector. It is possible to not have it in the correct orientation, or for it to shift during assembly. The holes have to be over the locating nubs or the seal will block fuel flow, even when prime is selcted.



Another question; did you make sure that the selector handle was oriented correctly upon reassembly?

 

Check the vacuum hose, check your fuel hose----,they both can collapse on the inside

Check the fuel tank cap's vent. If the cap seal is good, but the vent gets clogged/stuck--- you end up with a vacuum in the tank that will keep fuel from flowing

 

Because the rebuild was cheaper for the few parts I needed.

I'd imagine if they moved / raised up, then I'd never be able to get the chrome plate attached properly. Either way, I'll check it out.

The fuel line is new and doesn't appear to have any collapsing. The vacuum line is old, but I haven't noticed it crushing either. I tried running the petcock with the fuel cap open, but it didn't make a difference.

The inline filter seems to slowly fill on its own - like I waited overnight for it to fill up, which I cannot believe is normal.

Another disassembly will tell...

 

Stop.

Disconnect the fuel line and put a "catch pan" or something under the petcock or open end of the line to catch fuel.

Take the "engine" end of the vacuum line and VERY GENTLY "apply vacuum." (Suck on it.) It doesn't take much suction to operate the valve, which should then allow fuel to flow when activated.

If it works "manually" like this, you have a vacuum line issue of some sort. If it doesn't work, then you have isolated the issue to the petcock and need to pull it apart and carefully follow my instructions in the rebuild article. I have rebuilt a number of Yamaha vac petcocks using the described process and they have always worked fine afterward. Play close attention to the orientation of the plastic separator plate between the two diaphragms.

Another possibility is that the tiny bakelite disc isn't doing its job; if it allows airflow in both directions the petcock will "hammer" the diaphragm back and forth and pass very little fuel. Is the tiny disc "free" behind the brass fitting? If you shake the petcock in proximity to your ear, you should hear it rattling in there.