Rotax 503 not starting

[i3 roberto]

Ok ; your problem culd be in these bacum tube because its not the coorect
kind of hoose and you are loosig the pulse , you need a thick wall plastic silicone hose,or,rubber hose , it is very comoon problem the thinn walls of hosse absorbs the suction and the pump dont work

[Tinman]

Do you mean the vacume tube on the pulse line, it is the heavy pulse line from spruce aircraft...

[i3 roberto]

ok but put ties at hose ends check the signal from pick up coils , and value from the coil

[Bill]

Do like I do, cheat. Buy a can of lubricated starting fluid and shoot it into the vacuum port of one of the carbs. If it doesn’t start, or at least fire once or twice, you may have other issues - plug gap, timing, oiled plugs. If it runs and then quits - fuel issues.
Bill :-)

[nickjaxe]

Dont use any throttle when trying to start it just in case your are,

I always fill my bowls with fresh fuel from my jerry can.... dont have a hand primer pump...over here in the UK they are causing engine our due outlet valves sticking,

If its been stood for some time the jets may be plugged with varnish from old fuel,

Have you checked for a spark at the plugs...best done in a darkish place as the spark is not that bright,

Full choke no throttle mine fire almost right away every time.

Nick.

Nick.