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Old 02-19-2013, 02:41 PM   #1
Crisis management OP
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R80 fuel starvation?

I have a 1983 R80 rt which seems to be suffering from fuel starvation, there have been some odd electrical problems (since solved) which have muddied the waters a bit....
The bike runs well on a full tank of fuel but as soon as I switch to reserve (main "tank" empty) it splutters and struggles, only running well with full choke. Sounds like fuel starvation to me?
If I loosen a fuel line (tried this on both sides) there is a steady flow of fuel out of the taps with the petcocks in the reserve position.
Loosening the tank filler makes no difference either so there is no vaccum locking occuring that I can tell.
A couple of months ago I overhauled the carbs with new seals and jets and, as stated earlier, it runs well on the main tank setting of the fuel petcocks. The problem occurs as soon as the reserve setting is chosen.

Before I dismantle the petcocks (again, all was cleaned 12 months ago) and carbs in a wild hunt (for what?) does anyone have any suggestions?
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Old 02-19-2013, 02:47 PM   #2
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Clean the petcocks out, but also rinse the hell out of your tank. Make sure you get rid of any loose sediment in the bottom. Make sure the coating inside isn't flaking off and clogging it up, if so use a tank coating system to clean it up and recoat it.
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Old 02-19-2013, 03:22 PM   #3
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Ok, that sort of makes sense as a first step although I do have flow from the petcocks now, seemed to be sufficient flow to feed the carbs.
I will have a look tonight and clean it out.
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Old 02-19-2013, 03:31 PM   #4
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Once you get it running right, it will be a good idea to sometimes run the bike on the reserve taps to clear out out any water that may have collected in the bottom of the tank. It is surprising just how much water can be sloshing around there, especially in large tanks that don't get run down to the reserve level much.
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Old 02-19-2013, 03:52 PM   #5
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Sure sounds like a clogged "sleeve" on the petcock to me... I would pull the tank, lay it on it's side, remove the petcock, and clean the screens. You might want to tip the tank (with petcock removed!) and see how much smuck runs out..... !!!

And then add an inline filter, for belt-and-suspenders fuel cleansing!

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Old 02-20-2013, 03:52 PM   #6
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Thanks for all the replies, these are the findings:

First I removed the float bowls, turned the petcocks to reserve... a few drips came out both sides, no sign of water in the bowls.
Tried the same with the fuel lines disconnected from the tank, only got drips out of the petcocks.

Stripped the petcocks out both sides.
Let gas run out of each side into a clean receptacle, there were a few paint flakes, no water.
PO had repainetd the tank at some point, when I first got the bike there were flakes of paint in the tank, obviously needs coating inside which I will do later (need to use the bike now!)

Pulled the sleeves off the petcocks, there were more paint flakes on the outside & inside of the sleeve, cleaned and blew back through the valves, all looked good. Note there was no obvious blockage, there was 95% of the screen clear of any debris.
Re-assembled and gas ran cleanly out of both sides.

Re-assembled to bike, still no gas out of the float chambers!

When I overhauled the carbs I replaced the fuel lines and in line filters, less than 1000kms ago, yes, the filters are pointing in the correct direction.

Progressively removed portions of the fuel line and the filters were blocked! Blew through them (by mouth) and they were miraculously cleared, now everything works perfectly.

So, it appears that the blockages of both the petcock screens and the fuel filters is by some very small (invisible) particle which is readlily displaced with a bit of pressure ie: blowing by mouth.

That's a bit of a new one for me (is it a contamination in the fuel?), anyone had this occur before?
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Old 02-20-2013, 04:01 PM   #7
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Maybe an itsy-bitsy bubble of air in just the wrong place.....

Glad you got it figgered out!

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