Another problem with the turbo bandit 1200 (bike) I'm building. Have a turbosmart 38mm external wastegate with 7 psi spring. It doesn't seem to be functioning properly/at all. Boost continues to increase and I've seen as much as 11psi on datalog so its not just a slight spike. Still running engine in so haven't really given it the full beans anyway. The boost does appear to level off to some degree on datalog but that could just be as a result of the revs climbing.

Turbo is a td04 from a saab 9-5 and external wastegate is fitted for packaging reasons rather than because the internal one wouldn't have been up to the task (internal one welded up). Wastegate is fitted to collector at 90 degree angle which isn't ideal but I expected a decent external wastegate on a 200ish bhp 1200 engine would have a pretty easy job.

If I pressurise it with my bike pump it does open but I can't accurately gauge the pressure.

I wonder if it has been supplied with the wrong spring. Other then that I think I'm a bit stumped. Any thoughts?

If you tee in a boost gauge or even have the ECU running, engine off and tee in the bike pump you can watch the pressure build and wastegate opening. It does sound like wrong spring or pressure hose routed incorrectly.

If you can keep the gas flow as straight/smooth as you can it'll help, if theres room, remove the 90 bend if possible getting it as close to straight as possible. If a different spring still doesn't work get a bigger wastegate