Misfiring under load - help please!!

[Popell]

Update - seems to be sorted

Ok, been away and out of touch with the bike but have just swapped the plugs out for some Iridium NGKs.

Been out for a run and think the problem has gone - pulls like a train.

So thank you to all who made suggestions, just need to learn how to change a heated grip that remains depressingly cold - time for a search I think

 

[Mar5hy]

Can you explain the coil test again please?

 

[Bendy toy]

To test a coil start engine and disconnect the coil. If the engine runs rough disconnected but smooth connected, the coil is ok. If the engine runs rough either way the coil is not working.

Do all four then swap any suspect coils to the other cylinder. If the missfire follows the coil you have a coil fault. If the missfire stays on the same side you have a connection fault to that coil.

Ideally do this with new spark plugs to rule out a plug problem.

New plugs can mask a failing coil because they will spark better even with a weak HT feed.

 

[Mar5hy]

Sorry I have a r1100gs so my bike will only have 2 coils right?

 

[Steptoe]

Sorry I have a r1100gs so my bike will only have 2 coils right?

Forget all the posts above, they are for the 1200 models.. You have one single coil with two HT leads, one for each of your two spark plugs.

The 1200 doesn't. It has four spark plugs, with a coil incorporated into each of the four spark plug caps.

 

[Steptoe]

To test a coil start engine and disconnect the coil. If the engine runs rough disconnected but smooth connected, the coil is ok. If the engine runs rough either way the coil is not working.

Do all four then swap any suspect coils to the other cylinder. If the missfire follows the coil you have a coil fault. If the missfire stays on the same side you have a connection fault to that coil.

Ideally do this with new spark plugs to rule out a plug problem.

New plugs can mask a failing coil because they will spark better even with a weak HT feed.

You disconnect the connector at the top coil on each side. Then start the engine and see if it runs on just the bottom spark plugs.
It'll be obvious if one of the top coils or both have packed up.

You then reconnect the top connections and remove the bottom connections off the the coils, and see if the engine runs on the main coils.
It'll be obvious which, if any have failed without any faffing around.
Start to finish takes 2 minutes.
And no need to remove any of the rocker cover plastics as the coil caps don't need to be removed to do the test, the coil connection/plugs can be unpluged with all the covers in place