Mariner 3.3hp two-stroke - fuel starvation

[dunedin]

Our Mariner 3.3hp had been running fine. Accidentally restarted without opening fuel tank cutoff and air vent and motor died - but that is a common forget, and generally open both cutoff and air vent and runs fine.
But now it won’t run above idle without cutting out. Starts fine but any throttle and it dies.
Taken cap off tank to check plenty of fuel and no residual vacuum from running with vent closed.

These are not complex engines, and previously been very reliable. Serviced a couple of months back and new E5 fuel.
Any ideas what I have made go wrong - and most importantly how to fix?

 

[Aquaboy]

sucked a bit of crap into the main jet, just needs clearing

 

[jdc]

I have the same o/b which had with those symptoms. It turned out to be water in the carburettor. Probably not your cause, but draining the carb is worthwhile anyway - it only needs a screwdriver.

 

[andsarkit]

Probably worth taking the float bowl off and checking for muck. You need to remove a couple of screws on the case to get enough room to manoeuvre it out.
My 3.3 recently started pulsing with no real power. Cleaning the carb didn't help. It turned out to be a whisker bridging the spark plug. Easy to check if you unclip the small cover underneath.

 

[dunedin]

Thanks all. Will take a look when can find somewhere safe to dismantle/ fiddle - undoing bits over water won’t end well ;-)

 

[dunedin]

UPDATE: Got the dinghy ashore (so dropped bits wouldn't fall in the water)a week or so back to investigate. Checked
- spark plug - fine
- fuel flow from pipe in to carb - fine
- removed and stripped carburettor
Couldn't find any dirt or blocked jets (float chamber and main jet had been checked/ cleaned just a month earlier at service).

However, after stripping and rebuilding it seems to be back running fine. So a mystery why but resolved and thank for the help

The workshop manual was invaluable - found via MontyMariner site which was brilliant thanks - Mariner 3.3 Workshop Manual : Monty Mariner