I had a 4 cylinder Volvo Penta in my old Wellcraft/Manatee 18. It was the single carb (AQ125A ?) I think.
It is the same motor as found in Volvo cars except for the cam and cooling system so you can get parts at AutoZone and/or the junkyard.
Common to have head problems. For instance see:
http://www.baylinerownersclub.org/fo...hp?t-3104.html
Mine had a Solex carb which was a piece of crap. There were no bolt on replacements available.
I replaced the points with a Pertronix electronic kit. Well worth it.
What drive does it have? Most likely a 270 or 280. Both are good and can hanldle torque from even V-8's but take good care of them as parts are in the stratosphere. The 270 and most 280's only have a problematic electric tilt feature that can only be run all the way down and only tilted up with the engine out of gear for trailering. The 280 may have the optional hydraulic tilt and trim which much is preferred.
Make sure the cooling system is in order. Even used parts demand big money.
To me it would seem a little heavy and anemic for a V21. Make sure you are happy with the performance first but otherwise if it is in good shape and you take care of it I wouldn't turn my nose up at it.
BTW, I don't know what "due to venturi falling into head" means. Can you explain?
Steve P.