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Hi, I am looking for some advise / insights.

Problem statement: My TLR has been running great for the last couple of years. Recently it has started to spit/backfire through the front cylinder throttle body, with virtually no power (i.e. front exhaust pipe stays cool to the touch). Looking into the front throttle body, I can see flashes of light corresponding to the spitting/sneezing.

What could it be?

So far I have tried just about everything that I could think of to diagnose, including:
1. No ECU errors
2. Compression good at 180 lbs
3. Fuel pressure good at 47 lbs, fuel volume good at the return line.
4. No vacuum leaks (that I could find)
5. I have swapped/replaced just about everything on the fuel injection side, including ECU, wiring harness (+wiring the front coil directly to the ECU), fuel pressure regulator, TPS, ignition coils/leads/spark plugs.
6. Valve clearance check and adjustment (All but the front intake valves were .01mm tight, so initially I didn't touch the front intake cam, but.... On re-measuring, these front intake valves were ~.011mm and .012mm tight - hmmm - adjusted with smaller shims.

My plan going forward, re:re: measure valve clearance and intake cam alignment, re:re: measure compression and leak down.

Are these front intake valves somehow intermittently hanging up (i.e closing fine on the compression test, but failing once I fire it up?) Do I pull the head, and if so, what am I looking for? Could the front ignition coil somehow be getting the rear coil pulses?

Thanks!
 
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