FRUSTRATION! worked on heater fan and now truck won't start

[jwilson645]

This is a really weird thing and I'm fairly certain that the 2 things are not related because before I started working on it, I had it started up and running to warm up so I could test the heat. I didn't touch anything other than swap out the heater fan and put a jumper on the fan relay to find out it was bad. Now it only turns over but will not start. If I spray some carb cleaner in the carb it will almost run or run for a second but then backfire through the carb and die. This tells me it has spark.

Looking in the carb, i'm only getting spray on one side of the primaries. I just did a full rebuild on this Qjet a year ago, using all parts from Cliff's High Performance and made the changes that were suggested from him. It's been running perfect, aside from being a tad rich. I have a Summit fuel pressure regulator on it set at 5psi and a Napa mechanical fuel pump.

I think the whole thing is fuel related but the backfire has me confused. I haven't touched the timing or anything. Could a fuel issue cause the pop through the carb or was that likely because of me spraying the carb cleaner in there?

Engine was fully rebuilt by me with help here and has been running great until this.