I've posted regarding the Regina O2, but that is only one of my guesses.

After replacing the Head Pipe with an aftermarket piece, my 1990 8-valve 740 GL started setting a check engine light and the code read "can't regulate mixture" or something like that. My first thought was the O2 got to much abuse from the removal and reinstallation.

The new Head Pipe was made oddly where the forward O2 position would have it pointing at the ground, easily chilled and very likely broken off in normal driving. So I mounted the O2 back in the Cat. My second thought was this might be a bad place for the O2.

As this all happened simultainiously, so I'm not sure where to start.

Speaking of starting, it's been sort of hard to start (more cranking than my 240's) and recently after a low-rev. all-stumble, near-start was flooded.

Not sure where to look first - I use Dextron regularly and keep it well maintained and I dropped in a new set of Spark Plugs after it flooded. Faulty Fuel Injectors, Fuel Pressure Regulator - I'm stumped and the weather is not cooperating with me being outside trying to resolve it.

It hate working blind and dumb. Any advice, experience, suggestions would be welcomed.