Need help diagnosing problem

So I was out riding my bike and it was running great then all of a sudden it felt and sounded like I was running on 2 of the four cylinders was able to make it home checked the spark plugs they all looked good. Went to start it and nothing just turned over. Let it sit and tried again backfired so loud I thought it blew up. Started and ran. Reved up but won't stay running and doesn't sound right. Not like anything is broken just a rougher idle. I'm hoping someone has a check list I can go through to diagnose this.

1984 zx550

Sound like a bad coil or ignition pic-up.
Remove the spark plugs an check for sparks, #1/4 and #2/3 Shares a coil/pic-up.

No spark #1/4. Bad coil?

A multimeter or spare or the (temporary conected #2/3 coil) will tell you the truth.

Check to make sure that the wires are connected coming out of your ignitor. I had that problem because the connections just rotted away.

Try swapping the two coils. If the problem follows the coil the coil probably is the cause of the problem. If the problem does not follow the coil the coil is ok and the cause of the problem can then be diagnosed more easily. Ed

Swapped coils had spark from all 4. Ran good started running bad now no spark. Checked all connections everything looks good and plugged in. I guess I need to get an ohms meter

No spark #1/4 . Spark #2/3 now.

Do the 81's have points?

Everything after 1980 had electronic ignition.

To me it sounds like a faulty connection somewhere or an igniter going bad. If it was a coil he would have probably got it running on two cylinders... same with a pickup. The big backfire probably jolted the connection or igniter to start working for a while.

A timing light can show if sparks are dropping out.

I would inspect the wiring in the kill switch and ignition switch as they would be the first suspects. Next would be wiring harness from headlight to frame where it flexes for steering. Next would be any other connectors in the path.

Well I picked up an ohms meter tested everything turns out #1/4 on the pick up is bad. So I ordered a Dyna s ignition system and new coils.