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fuel petcock problem

Started by pwhitacre, July 28, 2020, 09:08:21 PM

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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.
86 fj1200  02 yzf-r6

red

Quote from: pwhitacre on July 28, 2020, 09:08:21 PMI 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 . . .
:yes:  
.
Cheers,
Red

P.S. Life is too short, and health is too valuable, to ride on cheap parade-duty tires.

FJmonkey

Check the tube/hose as it can be the leak source. The connections on either end of the hose/tube as well.
The glass is not half full, it was engineered with a 2X safety factor.

'86 Ambulance - Bent frame, cracked case, due for an overhaul
'89 Stormy Blue - Suits my Dark Side

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.
Past bikes : BMWR90-S,BMW R100CS, Ducati 900SD, Kawasaki GPZ600,Yamaha FJ1200,Kawasaki ZZR 1100 (4x),Kawasaki ZZR1200, Honda CBR1100XXX,Yamaha Thunderace, Kawasaki ZX10R (3X),
Aprillia Falco,Honda CBR600F4I, bikes today : Kawasaki ZX10R (C1, the best!),Yamaha FJ1200, soon to come Kawasaki Z900.....

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.
Peace & Love
86FJ 100K+
07Burg650
15Downtown300

red

Quote from: TomJK on July 29, 2020, 07:39:52 AMSome 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,
.
Cheers,
Red

P.S. Life is too short, and health is too valuable, to ride on cheap parade-duty tires.

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.
86 fj1200  02 yzf-r6

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.
86 fj1200  02 yzf-r6

Pat Conlon

Quote from: pwhitacre on August 01, 2020, 03:39:12 PM
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....
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

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.
life without a bike is just life

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.


Quote from: pwhitacre on July 29, 2020, 09:23:30 PM
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.
Past bikes : BMWR90-S,BMW R100CS, Ducati 900SD, Kawasaki GPZ600,Yamaha FJ1200,Kawasaki ZZR 1100 (4x),Kawasaki ZZR1200, Honda CBR1100XXX,Yamaha Thunderace, Kawasaki ZX10R (3X),
Aprillia Falco,Honda CBR600F4I, bikes today : Kawasaki ZX10R (C1, the best!),Yamaha FJ1200, soon to come Kawasaki Z900.....

Pat Conlon

Quote from: TomJK on August 05, 2020, 09:57:34 AM
... 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
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3