82 R100 - Keeps dying after running-out-of-gas

[motopoeta]

Hey everybody,

First time posting on Boxerworks. I was quite active on the K-Bike forums over at the k11og group but sold my K about a year ago (good riddance!). Have had BMWs for three years now. Love my 1982 R100 and if I had all of the money in the world, I'd probably just buy a cleaner one.

About a week ago, I ran myself out of petrol (I think that was the problem). Was just cruising down the street and thud, thud, thud, off. I came back to fill the bike up with gas and the sound was horrendous when I turned it back on-- like one cylinder was only firing. I made it about half a block down the street to the petrol station before she conked out again. I ended up having to push the bike home (and god was I sweaty when I finally made it home).

So here's what's up:

Whenever I fully choke the bike, it'll start up and sound godawful for about a minute and a half before it gives up and turns off. If I start it fully choked and ease off the choke, the second that I back off the choke, it'll die. It won't start unless it's choked.

At first, I thought maybe I had sucked something into the lines and buggered the fuel lines. This would make sense, as the vacuum created by choking it would force more fuel into the lines and would eventually flood the engine. So I pulled the lines off and checked to make sure that gas was flowing-- it was, and is. I can get a heavy stream out of both valves whenever I turn them on.

So I checked the plugs, and sure enough, only one would get hot. So, I switched the plugs. Still, one side was cool. So I figured it wasn't the plugs. Pulled the wires off to check if there was a spark getting to the plugs-- nope. Went up to the ignition coils, swapped them, and I managed to get a spark out of the dead side.

So I bought a new coil and threw it in. Started her up and she ran like she should for about thirty-seconds before again making that awful one-cylinder sound. Then she died. By this point, the battery was dead so I went to get it charged. Brought it back, threw it in and we're back to square one. Starts if its choked, dies if it isn't.

I'm completely out of ideas at this point. Would love some help.

Thank you everybody.

[vanzen]

Check:
Fuel tank, petcocks, petcock screens, petcock tubes, fuel lines, and float-bowls for rust, crud, debris,
or bits of that red fuel tank sealer that has come loose from the inside of the tank.
The least little speck of any of these or anything in the fuel delivery system
will disrupt fuel metering and cause all sorts of grief.
If evidence of any contaminants is found, get ready for carb disassembly and thorough cleaning.

[dougie]

Sounds like a blockage in one of the carb circuits on the side not firing.
Possibly some crud got pulled in when you ran out of gas. It doesn't take much to clog the idle/slow running circuit.

[motopoeta]

Check:
Fuel tank, petcocks, petcock screens, petcock tubes, fuel lines, and float-bowls for rust, crud, debris,
or bits of that red fuel tank sealer that has come loose from the inside of the tank.
The least little speck of any of these or anything in the fuel delivery system
will disrupt fuel metering and cause all sorts of grief.
If evidence of any contaminants is found, get ready for carb disassembly and thorough cleaning.

Checked the petcock and petcock screens, couldn't find anything. Checked the fuel lines, nothing. Checked the float-bowls, again-- nothing.

[motopoeta]

Sounds like a blockage in one of the carb circuits on the side not firing.
Possibly some crud got pulled in when you ran out of gas. It doesn't take much to clog the idle/slow running circuit.

Thanks Dougie. Suggestions on where to start?

[melville]

Suggestions on where to start?

Pull the jet with #1 on it, on the side that doesn't get warm. Look for a blockage. Poke it out with a fine strand of wire, or blow it out with air pressure. Reinstall jet and float bowl and see if there's any improvement in running.

If it feels like idle and low load stuff is improved, but WOT is not, do the same procedure on jet #3.

When you ran it out of gas, you may have gotten to the nasties at the bottom of the tank, making jet blockage a possibility.

Good luck!

[vanzen]

Remove and inspect the idle jet as motopoeta suggests.
With the offending carb removed from it's intake spigot, and while the idle jet is removed,
blow compressed air or squirt carb cleaner into the passage where the idle jet was seated.
You should feel a healthy stream of air, or see the cleaner squirting easily into the carb throat
from the holes just downstream of the throttle plate.
If not, you've found the problem.

Use soft copper wire carefully if you do any "poking about".

[Zombie Master]

Probably junk from the bottom. Get all cleaned up and don't forget to run your bike on reserve every once in a while, just to get some of the crap to clear out and into you new in line gas filters.

[Deleted User 287]

Great diagram, Dougie. I stole it. To whom should I give credit, if other than yourself?

[dougie]

Great diagram, Dougie. I stole it. To whom should I give credit, if other than yourself?

I don't remember from whom I got it, but it was someone here on Boxerworks.
(Hey! It was winter! That's a long time ago for an old guy to remember! )