ran up the 40HP yesterday after its small service and it sounded very good. A little feedback from Merc experienced people please!
Does the fuel primer bulb tend to overcome the carb needle valve and flood the carb? mine did but the jonnyrude ones tend to. I got a bit carried away pumping!
When starting from cold, do they usually need choke? I choked it and it fired/died on first pull and I think was flooded. It then took and age to start but went off choke with throttle well open but of course needed revs dropping back asap to prevent it revving its nuts off! The poor start could relate to point one though!
I have detected a small water leak. There is a drip about once a minute from around the port side coil. I have not been able to trace it yet but it looks like the thermostat cover is up near it and other water gaskets. It does not seem to be from head gasket and it has good compression on both cylinders when I checked it.
Sadly this leak will have to stay for our planned run next week.It is very very minor.
General Merc queries
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petrolhead
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Re: General Merc queries
Yes you can flood the carb(s) when priming if you get a bit over enthusiatic! 
Normally you would start from cold on full choke, then take the choke off the moment she starts & she should be away. You will need to find where to set you throttle for fast idle with experience, I think the 'books' say move the warm up lever (or controller lever in your case) to fwd to its maximum but in some cases this is far to much when they fire up.
Don't know on the water leak, I have no experience with your later 402, I didn't know they even had a thermostat (are you sure it does?) as most Mercs from that era & earlier don't. What you refer to as the cylinder head - isn't. It's just a water jacket cover. Again early Mercs (& this is an early design) had the head all cast in & the pistons are fitted from the bottom (see picture of a 50hp block which illustrates this nicely).
Normally you would start from cold on full choke, then take the choke off the moment she starts & she should be away. You will need to find where to set you throttle for fast idle with experience, I think the 'books' say move the warm up lever (or controller lever in your case) to fwd to its maximum but in some cases this is far to much when they fire up.Don't know on the water leak, I have no experience with your later 402, I didn't know they even had a thermostat (are you sure it does?) as most Mercs from that era & earlier don't. What you refer to as the cylinder head - isn't. It's just a water jacket cover. Again early Mercs (& this is an early design) had the head all cast in & the pistons are fitted from the bottom (see picture of a 50hp block which illustrates this nicely).
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petrolhead
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Re: General Merc queries
for once I am not too thick, I know the water jacket cover! I did mean cylinder head, in that the leak was not it seems coming from that and no waterways were leaking into the bores.
Yes, it started on choke and full throttle and reved its nuts off! with only muffs it alarmed the neighbours as both my dad and Ken over the road came to see what pile of poo I was playing with this time and thought I had got a Trabant
I washed the boat off too! needs a polish and may not get it for its forst run but I did hose through all the inside and scrub it up plus spent hours clearing it out so the draining worked to the hole from all areas! got all sorts, sun tan lotion bottle, sweet wrappers, a ball of string and a piece of copper pipe out!
Talk soon
I did mean cylinder head, in that the leak was not it seems coming from that and no waterways were leaking into the bores.Yes, it started on choke and full throttle and reved its nuts off! with only muffs it alarmed the neighbours as both my dad and Ken over the road came to see what pile of poo I was playing with this time and thought I had got a Trabant
I washed the boat off too! needs a polish and may not get it for its forst run but I did hose through all the inside and scrub it up plus spent hours clearing it out so the draining worked to the hole from all areas! got all sorts, sun tan lotion bottle, sweet wrappers, a ball of string and a piece of copper pipe out!
Talk soon