While I have a good sense on how this engine should perform in a v runabout, I do not have experience with a deck boat. My assumption is a heavy boat but large planning surface, but still on the slow side. Multiply that by the elevation. My boating has been 2K' or lower.
Do you know what the original boat/305 pkg expected performance, at normal elevations?
Not sure I know how to do the Multi Quote thing??
Some info on a Mariah web page indicates a 4.3L is a little under powered but a 5.7 Mag can reach close to 60 mph at sea level of course. It is a pretty good size boat but does have a V-hull design
Was it ever tested at a lower elevation, prior to purchase?
Yes, the marina said the tested it before trade in. I have recently called them and he swears it ran great at their 2000ft elevation - he even became a little perturbed and said I was calling him a liar which I was not directly.
I assume this was an "as is" sale from this dealer. ie no warrantee?
He might take it back if it just wont' run at this altitude.
I guess my point is, even though the unknown motor and severe performace problem may be connected, need to click off other items on Don's Checklist. The comment about water logged foam, can still be a possibility. Not sure I would cut a hole (but if you are ok with it there are hatch plugs that can be used), but you can take it to transfer station scale for weight reading of the boat and trailer, and then just trailer, + calculate gas and gear, to compare to factory weight.
Thats good idea. I think the weight is in the 3K-3.5K range
A few more comments on carb. The 1/4" is probably OK. It will open some once the 2ndarys open. The 3/4 turn comment does not sound like the Merc service manual set-up, though. I believe it uses a gram scale. You should use their data vs any generic carb kit instructions. service manual #17, in the "Adults Only" section.
The 3/4 turn is a typical Q-jet setting. I'll try to figure out the service manual procedure but it seems complicated.
I don't think the issue is advance, but doesn't take long to map. The standard 5.7L 2brl, doesn't come all in to around 4K. You are getting about the right advance for the rpms you are turning. If anything it is too high. Only question is, can it advance any further.
Ratio is also stamped on drive input shaft, but don't think you want to pull drive for the info. You could turn the motor over by hand and count the revolutions to turn the prop 1 time. 1.5 engine revolutions = 1.5 ratio, 1.65 rev = 1.65 ratio. A little hard to be exact, but probably close enough.
