I have a 2003 speedmaster 800 only firing on right cylinder. ive changed plugs and swapped coils around to see if it was them. but the coils seem to be good. i trailered to bike to go take rooad test on and on my way home it rained pretty hard. a couple days after is when this problem developed. can anyone help me out here?

Best to get a new set of wires, if you swapped around the wires and it's not bad wires you need a new spark /coil pack, but as long as you need a new one its best to put on new wires and plugs, not to much if you do it yourself.

bad coil

P0300 Random Misfire Detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0303 Cylinder 3 Misfire Detected
according to this fault codes first mark ignition coils
3 ---------------- 6
2 ---------------- 5
1 ---------------- 4
RB-------------LB
this right banks and left bank, please remove Ignition coils with lids and spark plugs from right bank and swap with left bank, if fault code change as
P 0304 Cylinder 4 Misfire Detected
P 0305 Cylinder 5 Misfire Detected
P 0306 Cylinder 6 Misfire Detected
You can Identify it's a faulty ignition system then next swap ignition lids from ignition coils be careful each coils have two lids one short and other long bit deference and when you remove and fix it to the car keep in mind correct order because each coil two different fire for two spark plugs don't mix up, if you mix it can create the fault code.if you detect any fault ignition coils or spark plugs or lids replace that and also whether god or bad recommend to replace spark plugs, find the right that's most important thing, if this way couldn't found the any ignition fault next step is check fuel presser, when the engine running fuel presser must be around 4.5 bar without engine running must be 4 to 6 bar if the fuel presser too low need to check two different things one is fuel pump other is fuel injectors, in this case you can swap injectors from right bank to left bank and find is the injectors leaking, if not leaking faulty fuel pump.is this information helped you? if yes please leave a comment,

bad ignition module or pickup coil...or wiring to the components could cause the ignition to fail... also check plug caps ,plugs and wires

Hi
With Ignition switch off :-
1st Check for bad connections, broken/crushed wires, continuity & resistance between the cap, HT lead, coil, ignition coil primary wires
2nd Disconnect the CDI unit from its connector & check for the same between the loom side of the connector back to the coil
3rd Check coil is earthed

If all OK suspect the CDI unit but double check everything first( there are some more checks as well), as these are very expensive

Ride safe
Bike-Doc

Please rate this solution well if it has helped !!
Any comments welcome

do you have coil over plug or one coil? if you have spark plug wires, swap one with the cylinder in question. swap an injector.

Triumphs have a habbit of the ignition coils failing past a certian age. Switch the coils around and see if the backfires transfer with coil.

The reason I'm asking this is because a dual coil fires BOTH plugs at the same time. If one plug doesn't fire right, the other won't either, even to a point that neither does. Kepp the coils where they are and swap the plugs and wires and see if you have a change. Let me know

You didnt mention having changed the spark plug wires, so that is another item that could be culprit as well. As well, it could be a coil pack that is not working properly.

I cannot recall at the moment if that model year uses coil on plugs or if it uses coil packs. Either way, if it uses a coil on plug set up, take the one for the #3 cylinder and move it to say #4 or anyone of your choice and see if the misfire follows

If it uses coil packs, there is likely one coil pack that controls two cylinders. In that case just swap the coil pack with an adjacent one and see if the problem follows. Pay attention to where the spark plug wires go because it will be an issue if you get them mixed up. You just swap the coil packs around.

I would, however, start with the spark plug wires if you have not changed them already.