Misfire, carbs or coil?

Dermott · Apr 28, 2020

Was planning an all oils service, so ran my 1996 R100GSPD on private lane to warm up. One cylinder dropping all power intermittently, coming back in surges and poping and farting. running fine at idle and blipping the throttle. changed oils and plugs, cleaned around coil and sprayed WD40 all around. still the same. Ran fine before I parked up in a shed before the winter, and started it a few times to check the battery.
Could it be carb diaphragm? how do they behave when leaking?

mikeyboy · Apr 28, 2020

Sticking floats/ needle valves?
If it’s been laid up the carbs will prob need a good clean

r100gser · Apr 28, 2020

Do all the easy to check things first, if no change check the valve clearances and if one is sticking...good luck

DrFarkoff · Apr 28, 2020

Likely deconstructed fuel in the carb blocking a jet or a plug wrecked by starting and running for a bit before switching off again

Or could be condensation in the tank being picked up in carb if the tank was not filled before you parked it up ??

WD40 is satans Piss!! Keep it away from rubber components

A good clean of the carbs Diaphragms "usually" make their presence known range plus

Kenny · Apr 28, 2020

If above doesn't solve anything, could be hairline crack in the coil ( WD40 won't fix it )...which opens up when hot and causes a misfire. Swop plug leads over from coils and see if problem goes to the other side.
Needs a replacement coil if cracked..cannot be repaired properly.

ChasF · Apr 29, 2020

I had similar symptoms after the bike wasn’t used for a couple of months - only misfired under load. It turned out to be the coil, the crack was very obvious. Replaced with the expensive one from boxer supplies but apparently secondhand K100 coils are a good option.

The Other PaulG · Apr 29, 2020

Kenny said:
If above doesn't solve anything, could be hairline crack in the coil ( WD40 won't fix it )...which opens up when hot and causes a misfire. Swop plug leads over from coils and see if problem goes to the other side.
Needs a replacement coil if cracked..cannot be repaired properly.

I had this too. A bike that only misfires when warm must be a mixture issue, right? Wrong, took me ages to fix because of my blinkered thoughts.

Gummed up carb passages, damaged diaphragms, coil... I bet you sort it if you look at just those three.

MickDB1 · Apr 29, 2020

It could be the HT leads too. I had the metal cap live on one side once.
Swap the leads over as Kenny said

Dermott · Apr 29, 2020

Had a quick look this morning, checked float chambers, tiny bit of something in the bottoms, behaving like water but not water, will misfire on hard twist of throttle in neutral, tried pulling plugcaps sparks jumping everywhere, not smart

.
will try diaphragms later and or full carb strip.

Dermott · Apr 30, 2020

Cleaning carbs today, diaphragms seem ok, but I noticed one carb had a rubber cover on a nipple under the intake side of the body, and the other with no cover and venting into the air flow. How do I attach photos from phone when using phone to send messages

mikeyboy · Apr 30, 2020

Dermott said:
Cleaning carbs today, diaphragms seem ok, but I noticed one carb had a rubber cover on a nipple under the intake side of the body, and the other with no cover and venting into the air flow. How do I attach photos from phone when using phone to send messages

That would do it :thumb2

DrFarkoff · Apr 30, 2020

Dermott said:
Cleaning carbs today, diaphragms seem ok, but I noticed one carb had a rubber cover on a nipple under the intake side of the body, and the other with no cover and venting into the air flow. How do I attach photos from phone when using phone to send messages

Have a another wee Look again up from below? Bings should have a screw in that port

They have a wee habit of backfiring every now and then and wee rubber doofers would get blown off

Part one here https://www.realoem.com/bmw/enUS/showparts?id=0484-EUR-01-1996-47E2-BMW-R_100_GS_PD&diagId=13_0469

Dermott · Apr 30, 2020

https://photos.google.com/photo/AF1QipPMcrbdnJEyNYz5I8BnFm9DBTakzAPsz-KhCLVi

solidstate100 · May 1, 2020

Dermott said:
https://photos.google.com/photo/AF1QipPMcrbdnJEyNYz5I8BnFm9DBTakzAPsz-KhCLVi

Linky no worky

Jockser · May 1, 2020

Dermott's carbs

<a data-flickr-embed="true" href="https://www.flickr.com/photos/139151959@N08/49841457827/in/datetaken/" title="20200430_182152"><img src="https://live.staticflickr.com/65535/49841457827_bd7f9ee4ef_4k.jpg" width="4032" height="3024" alt="20200430_182152"></a><script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

Is it just me or does that pic look very elongated :nenau

dean0n0 · May 1, 2020

Looks more like Dali's carbs.

patrick · May 1, 2020

I had similar with moisture migrating into the moulded plug caps, snipping them off and fitting screw on ones proved the point then I replaced with new and all good.

BillN · May 1, 2020

Kenny said:
If above doesn't solve anything, could be hairline crack in the coil ( WD40 won't fix it )...which opens up when hot and causes a misfire. Swop plug leads over from coils and see if problem goes to the other side.
Needs a replacement coil if cracked..cannot be repaired properly.

Have you checked this?

Jockser · May 1, 2020

Poor bike is just sitting there awaiting a 'fix'...

Nice bike lift Dermott, did ya wheelie it up there

MickDB1 · May 1, 2020

I used to "Hang" my bike. I thought it was cool - but I still got a bench as it dont wander about as much when I thrape summat with me hammer

Misfire, carbs or coil?

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