Hi, Louis and the usual suspects are:
1. A severely drained battery.
2. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
3. Faulty main circuit breaker and or connections.
4. Faulty ignition coil and or connections.
5. Faulty spark plug, oil or gas fouled, wrong heat range or service type, wrong gap, loose in the cylinder head, broken electrode or insulator.
6. Faulty spark plug cables, leaking or broken, internal damage.
7. Faulty ignition module, switch, CKP, MAP, CMP, sensor and or any connector in the ignition circuit could have corroded, loose, or broken pins/sockets
8. Burnt exhaust valve or air leak in the exhaust system.
For more information about your issue, please visit the websites below. Good luck and have a nice day. RT 1100 backfire burp or R1100rt back firing 1993 2000 BMW R1100RT R1100RS Service Manual Moto Data Pr BMW Motorcycle Parts Fiche OEM BMW Motorcycle Parts online 1970 present BMW BMW Motorcycle Parts Fiche OEM BMW Motorcycle Parts online 1970 present BMW