Cannondaleriders

so needs to be about 60 psi. a spares shop?

Its got nothing to do with your filter or fuel flow. When the engine die when and give the injector a b open fault feel if the fuel pump is hot. Mine got so hot taht you could not touch it with your hand. It was seizing up and took to running temp for the pump to get to running heat and lose pressure because it seized.

Any shop where you can buy parts for cars and vehicles. Any shop that sell a pressure gauge.

So more than likey its a bad fuel pump.

Before looking at a hundred other things check this first. My Dale did the exact same thing and it was the fuel pump. I looked at everything else and it ended up to be this after a lot of frustration and time.

Its possible to get injector a or b open faults on perfectly fine running quads. If your battery is low or connections are poor the ecu senses deviations in voltage between the pos and neg sides of the injector tripping the code. I just had marginal battery that could only crank the quad slowly and barely get it running do this. I checked the wiring and injectors ,found nothing wrong. Installed a good battery and the codes went away. So if the engine runs fine and you get the code oad test your battery and check the charging system.
A fuel pump with using more juice than it should could also cause a similar situation .