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What can go wrong with a fuel petcock?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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I've found that fuel flows from the tank whether I've got the tap in the Reserve, On or Prime position. I know the petcock is only meant to allow fuel through when the engine is running (or when it's in Prime position) but I don't know how it does this and I didn't know what to expect when I took the petcock apart. I've removed the petcock from the bike but can't see anything obviously wrong or anything much that could be wrong.
The petcock has a plastic filter thing that sticks up inside the fuel tank. The mesh filter is intact.
I removed the 4 screws on the vacuum pipe side of the petcock and removed the vacuum pipe. There's a diaphragm there with a sort of nipple in the middle with a washer round it. The diaphragm seems to be intact and the washer seems fine. If I pull up gently on the nipple and then let it go, the diaphragm gradually sinks back down. If I put my finger over the vacuum pipe before letting go, the diaphragm stays 'inflated'.
I've taken the actual tap off but can't get any further. Inside is the plastic barrel that the tap turns. Should I be able to get that out?

I know I can order a petcock repair kit from somewhere but I'd like to know what is wrong and what bit I'm actually repairing. Also, I need a quick fix for this problem, even if it's only temporary.

All advice gratefully received.

Happy new year.

Roger
 
The plastic barrel has a rod on the other side of it that pushes on the diaphram in the prime position to allow fuel to flow. That rod has about one-half of a loop of spring built into it at its base. You may need to shorten the length of that rod/spring so it doesn't contact to the diaphram in the run and reserve positions. Don't cut the rod, just vary the length of the coil. Be careful pulling out the barrel. Pull it straight out so you don't mangle it by turning it further than it was meant to be turned.
 
Thanks. Just putting the petcock back together seems to have fixed it (for the time being at least). I think I must have pushed the barrel further in and so effectively shortened the spring you refer to. I'll try to get hold of a petcock repair kit or a new petcock.
However, despite draining the carbs and cleaning up the plugs, the bike still won't start - it still seems to be too rich.

Roger
 
Petcock clearing

Petcock clearing

If you remove your petcock, dismantle it and look in the cavity where the barrel turns, you may find that the main supply opening to the tank is filled with debris (silt and such). Clean it with a wire that you have flattened the end with a hammer to make a tiny scraper tip. 1/2 inch from the end turn it 90 degrees. Then you will be able reach into the opening and clear the blockage. Clean it thoroughly with carb spray.
 
Phill
Thanks - my 'fix' of the petcock turned out to be very temporary. I'll give your suggestion a go.

Roger
 
I had a simliar problem but then i took it apart and sprayed carb cleaner all over and through it and it worked...but now a week later when i give vacume to the line when on prime the the tank will only flow for as long as i am applying vacume whats wrong?!
 
You need to lengthen that rod I spoke of that is behing the plastic valve. That pushes on the diaphram allowing fuel to flow on prime. If you get it too long fuel flows in every position. You have to adjust that rod until you get it right. It has a spring built into it that you can lenghten or shorten. Be sure to pull that valve straight out.
 
ok cool, Just to make sure am i right about the prime and regular position?

on prime vacume only needs to be initiated and it will continue running.

on regular vacume must be constant for flow
 
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