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Bmw r80 intermediate missing

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Big mac
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Joined: 10 Oct 2019
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PostPosted: 10:43 - 10 Oct 2019    Post subject: Bmw r80 intermediate missing Reply with quote

Hello all any help would be much appreciated. I bought a 1984 bmw r80 a couple of months ago and all seemed great then it started missing on one cylinder. When it starts missing there's no loss of spark at the cap I popped each one off with it running and believe me it's got a spark. I've changed the plugs stripped the carbs and replaced the seals motorworks seal kit. Made sure the tanks clean. Removed the in line filter from the fuel line.
Not sure what else to try the bike runs fine seems to happen when the throttle is in one position on a long straight road
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The Shaggy D.A.
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Joined: 12 Sep 2008
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PostPosted: 13:20 - 10 Oct 2019    Post subject: Reply with quote

Can't remember my R100RT, but does it have twin coils that both fire at the same time? If so, can you swap the coils and see if the fault moves to the other cylinder? You might get a spark with it out of the cylinder, but under pressure of the cylinder stuff changes.
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MCN
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Joined: 22 Jul 2015
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PostPosted: 18:40 - 10 Oct 2019    Post subject: Reply with quote

Svapp ze coils (and ht leads should be a suppressor in the cap or lead.) as advised.
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davebike
Nearly there...



Joined: 15 Nov 2013
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PostPosted: 09:31 - 11 Oct 2019    Post subject: Reply with quote

check the advance retard unit well know in the trade for this type of issue !
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jnw010
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Joined: 22 Nov 2012
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PostPosted: 12:44 - 11 Oct 2019    Post subject: Reply with quote

As above, either coil or advance retard unit.

My dad had an R100RS that he put 150k+ miles on and had the same problem a couple of times. One cylinder cuts out completely, and then while you're full throttling forward on the one remaining cylinder the other one cuts in with SURPRISE!
Apparently it makes riding the bike more difficult.
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MCN
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Joined: 22 Jul 2015
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PostPosted: 18:19 - 11 Oct 2019    Post subject: Reply with quote

jnw010 wrote:
As above, either coil or advance retard unit.

My dad had an R100RS that he put 150k+ miles on and had the same problem a couple of times. One cylinder cuts out completely, and then while you're full throttling forward on the one remaining cylinder the other one cuts in with SURPRISE!
Apparently it makes riding the bike more exciting


I fixed that for you. 😉
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bikenut
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Joined: 21 Nov 2011
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PostPosted: 10:31 - 12 Oct 2019    Post subject: misfire Reply with quote

To fully "see" if ht is lost to that cylinder with bike stationery or whilst riding, think about getting those red neon plug caps that flash when ht passes thru them. You may have to make a "converter" for connection but you would be able to see them whilst riding.

Loss of compression when the engine warms up?? check valve working clearance and compression pressure when cold and when hot, just to rule that out.

Else see the ign advance etc..

You have a wiring diagram that will show if its wasted spark.
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