Homebuilt aircraft pilot reported fuel pump and engine malfunctions and diversion to closest suitable airport.

Narrative

Highly modified homebuilt aircraft; using a Continental O-200 engine with automotive style fuel injection and electronic ignition with automotive spark plugs. The fuel and ignition controller was manufactured by RWS who is no longer in business. This installation has been used in my aircraft since year XXXX and had approximately 500 hours of operation. It has two Walbro automotive fuel pumps mounted in parallel for the fuel injection system. The #1 pump is normally used while flying West and #2 used while flying East. Both pumps are normally selected during take off and landing phases.This flight was planned from ZZZ to ZZZ1; approximately 520 miles; and I was running on the #2 pump. I was at 7;500 feet. About two thirds of the way through the flight I got a LOW PRESSURE alarm on my Dynon EFIS (Electronic Flight Instrument System) and the engine got very rough. The pressure is normally 40 PSI but it had dropped to about 25 PSI. I switched to the #1 pump and shut off the #2 pump and continued with the flight. I estimated arriving at ZZZ1 in about 45 minutes.After a while; the engine started running rough again. It was very subtle at first; then got rougher. I did an ignition check; selecting either the top plugs or the bottom plugs and found the engine ran extremely rough on the top but fine with the bottom plugs. At this point I decided to get on the ground and landed at ZZZ2; about 35 minutes short of ZZZ1.A friend flew over from a nearby airport over to help me. I pulled the cowling and found the #3 top plug was fouled and I replaced it with a spare that I had carried. With the new plug; the engine ran up fine on the ground. However; I still had the issue of the bad #2 fuel pump.To replace the fuel pump is a fairly involved job; since it is located behind the pilot's seat. The tail has to be removed; cables disconnected - it's a big job. The attendant at the airport said I could stay in an empty hangar for two days; but that was all. No other space available. Also; we called around to some auto parts stores and this fuel pump is not locally available. So; I was faced with the prospect of having my friend fly me back to ZZZ1; try and borrow a truck and trailer; drive the 140 miles to ZZZ2; disassemble the aircraft enough to load it and bring it home; all within two days.After running the engine on the ground several times I decided to fly it the rest of the way home. My friend agreed to fly chase in his aircraft. I climbed to 7;500 feet and headed home. For some reason I was getting high temperatures on cylinders #1 & #3 but was able to manage it by reducing throttle. Though I was somewhat nervous; the flight itself was uneventful.Two days after the flight I realized I probably violated 14 CFR 91.7 'no person may operate a civil aircraft unless it's in an airworthy condition'. Even though there are two pumps; a fuel pump failure could mean the aircraft does not meet its certified airworthiness standards; because both pumps are typically required for redundancy. I realize that I should have gotten a Special Flight Permit (Ferry Permit) to fly my aircraft home.