fuel petcock problem

[pwhitacre]

I recently needed to drain the fuel tank on my 86 FJ so i hooked a hand held vacuum pump to the petcock and found it would not hold vacuum. The petcock worked as long as i kept pumping but would leak down as soon as i stopped. I replaced this petcock about ten years ago so i was not expecting it to be bad again. I bought a rebuild kit from RPM but it made no difference. Is there something else i need to do when testing it other than just the vacuum pump? Any help would be greatly appreciated.

[red]

I recently needed to drain the fuel tank on my 86 FJ so i hooked a hand held vacuum pump to the petcock and found it would not hold vacuum. The petcock worked as long as i kept pumping but would leak down as soon as i stopped. I replaced this petcock about ten years ago so i was not expecting it to be bad again. I bought a rebuild kit from RPM but it made no difference. Is there something else i need to do when testing it other than just the vacuum pump? Any help would be greatly appreciated.

pwhitacre,

I can guess two possibilities, from here:

1. Ten years is long enough to expect a re-work of the vacuum petcock to come due.

2. Your vacuum pump or the hoses are leaking air back in, not the petcock itself.  FWIW, you can use a good hose and apply your mouth vacuum to open the petcock (it doesn't take much vacuum to open the petcock).  Cap or pinch off the hose firmly, and see if the petcock keeps flowing fuel.  If so, then the pump or the its' old hoses are bad, not the petcock.

My US$.02 worth . . .
 
.

[FJmonkey]

Check the tube/hose as it can be the leak source. The connections on either end of the hose/tube as well.

[Old Rider]

I had the same problem it was still leaking vacuum after replacing the membrane .It turned out to be leaking air on backside where the
wires that adjust how much fuel flows goes in  .Read the last in my post here :If you plan ti fix it same way i did be sure to use fuel and heat resistant silicone.
http://www.fjowners.com/index.php?topic=19388.0

[TomJK]

Hi

Some FJ1100/1200 guys in Germany, build in a fuelpump, like the later FJ1200 models, and that seems to work fine...I put in a Hardi Marine Fuelpump, German made, works fine.

Cheers, Tom.

[TRoy]

....hold on a sec .... isn't there a tiny little pinhole airbleed made into the petcock? , ....as in 'its not supposed to hold vacuum 100%'

..seems I remember a discussion about this umpteen years ago.

[red]

Some FJ1100/1200 guys in Germany, build in a fuelpump, like the later FJ1200 models, and that seems to work fine...I put in a Hardi Marine Fuelpump, German made, works fine.
Cheers, Tom.

Tom,

Hardi makes many fuel pumps, both automotive and marine.  Do you know which marine fuel pump you have there?

Before installing the fuel pump, did your bike have a fuel pump, or gravity-feed fueling originally?  Did you need to replace any carb parts, to suit the pump?

Thanks,
.

[pwhitacre]

I know my vacuum pump is good as i can disconnect the hose from the petcock and put my finger over it and the pump does not leak down. I did notice on the petcock there is a small round area that looks like it could be some sort of a vent and if i put my finger over it the leakdown is slower but still leaks down.

[ajacstern]

When I rebuilt my petcock it held vaccuum pretty well, that was with a syringe test. I would not be surprised if it needed to be rebuilt after 10 years. When you just rebuilt it did all the metal look clean and in good condition? Diaphragm not pinched anywhere? I don't expect these to hold perfect vaccuum but on a short timescale I would expect them to hold well.

[Old Rider]

Here is a pick explaining the backside petcock air leak.

[pwhitacre]

I appreciate the pic of sealing the wires, i had read that post when i started trying to figure this out and tried it on mine but it did not help. I guess i will order a new one from RPM. Thanks to all for the input.

[Pat Conlon]

I guess i will order a new one from RPM.

If you can live without that wonky reserve, the '84/85 petcocks are plug and play for less money.
You can then re-purpose that reserve rocker switch for something useful....

[andyoutandabout]

Sage like words as always from Mr C. My petcock did it to me on a trip this time last year. Replaced with the earlier, non electronic model. Also cheaper to boot. RPM made life easy. And back on the road again.

[TomJK]

Hi

I already had a fuelpump, but i know from German FJ riders, that they just fitted the pump on an older, non fuelpump FJ, if they had to change from 8 to 6 mm diameter fuelline I have to ask...

I will try and find the type I used...

Cheers, Tom.

I know my vacuum pump is good as i can disconnect the hose from the petcock and put my finger over it and the pump does not leak down. I did notice on the petcock there is a small round area that looks like it could be some sort of a vent and if i put my finger over it the leakdown is slower but still leaks down.

[Pat Conlon]

... i know from German FJ riders, that they just fitted the pump on an older, non fuelpump FJ, if they had to change from 8 to 6 mm diameter fuelline I have to ask...

Hello Tom, a couple of things to do if you want to retrofit a fuel pump on to your early '84-87 FJ.

1) the '84-85 vacuum petcock must be set on (P) Prime (open all the time)  For '86-87 petcocks that don't have this prime feature, you have to convert to a manual petcock or use a '84/85 petcock.
http://rpmracingca.com/proddetail.asp?prod=M%2FC%3AFJPetcock
The closing of the petcock is no longer needed, the fuel pump now controls the fuel flow.

2) The '84-87 gravity feed carbs use larger float needle seats, the '88-95 fuel pump carbs use smaller float needle seats, so you will need to change them: http://www.fjowners.com/index.php?topic=9836.0
If you use the large needle seats with a fuel pump, the higher fuel pressure will push the float needle off the seat and not allow it to fully close and flooding will occur.

3) Add a safety shut off for the fuel pump. On the '88-95 Fuel pump FJ's the fuel pump power circuit runs thru the ignition box so when the ignition box stops sensing a tach signal (engine stopped) the power to the fuel pump stops after a few seconds.
You need to add this Safety feature to your early FJ: http://www.revolutionelectronics.com/Products/Fuel_Pump.html

Everything else is straight forward, pump, wiring, fuel filter, fuel line, etc...

Cheers.  Pat