Saving Old Seagulls

Acquired an FV ....stripped as much as needed to get it running
fuel system & tank fully stripped and cleaned

overhauled the magneto and set points ...set it up with a known good HT lead

starts well in test tank, on 10:1, sounds great, pumps very well....then slows, burbles and gurgles and finally stops

in this later stage anything off full throttle it dies
noticed at this 'dying stage' it's blowing air out of the carb inlet instead of sucking in ...fuel collecting in the air intake bell mouth

Also seems to be blowing a bit of water out of the drive tube holes

let it get cold and it's the same all over again ...starts straight away but after 10 mins misbehaves again

any hints ????

I am thinking air leak into crank case.

Its easy enough for water to get into the drive tube ( and not uncommon I think ) but if it is 'blowing' out of the holes that seems to imply some pressure in the tube, easiest route for that would be blowing past a worn main bearing perhaps?

Would imagine said leak getting worse as something expands when hot could cause the final 'dying'. No suction at carb also says air leak too.

Hmmmm ....
I hate bad news that involves spanners, oil and muck

so shall try to defeat it with elegant logic ...

if a worn bearing, or slight gas escape past the rings that would pressurise the drive tube to prevent water bubbling out ???
or try to escape out the top into the u/s of the magneto ???

the 2 1/2's of the crankcase require sealing given its a 2 stroke and needs the vapour bourne lubrication on induction ....

Hmmmm..... leakage past the piston only thing that could provide a back pressure to 'puff' out the carb inlet

sh*t... bad news that involves spanners, oil and muck

I hate bad news that involves spanners, oil and muck

Surely spanners oil and muck is what a Seagull is all about. That's why we luv 'em.

something to do with carb?
filler cap air hole is not blocked?

Neal you immediately made me think of some kind of comic book super hero for some reason:

' Behold! I shall defeat your puny gungy problem with my elegant logic '

I feel more like 'Bicycle repair man' for those who know what I am going on about

You could be right re bore / rings, but wouldn't that get less as motor warms up and piston expands? mind you, rings could stick as they get hot.

Sorry but I think its time for M.C. Spanner. Let us know what you find