Water head pressure yamaha V-max?

[brownies]

1st time start with muffs on a 97 150 V-max. Been setting for about two years. Removed from boat that was dry sunk

• . Fired up no problems, but, no head pressure. Pulled the line off the top of the head. No water up there.<br />Changed water pump (correctly). Pee hole stream good. New thermostats (but, thats after the pressure port). Poppet valve okay. <br />With lower unit off, pressure from the inlet pushes water out the top (no restrictions from either direction). <br />When muffs are attatched to lower unit only (on bench).. You can see water coming out of the pump...and...lots coming out by the prop. Sumerging lower unit...runs cool with small amount (7lbs) of head pressure (benched/idle)<br />The question is...WHY can this engine not be run on muffs...seems to not get enough to the pump and most water flows out by the prop. Is this right?

 

[jim dozier]

Re: Water head pressure yamaha V-max?

Does this engine have a high water pickup in front of the trim tab? Some engines need this blocked off (duct tape) when using muffs.

 

[brownies]

Re: Water head pressure yamaha V-max?

No other water intakes that I can see. Unless it's a hole the size of a speedo port. <br />I started with the water pump, then began pressurizing coolant ports (outlets) from the bottom up, and then top down. Obstructions rules out, I went ahead and replaced the thermostats and the poppet valve. Then removed the lower unit and "muffed" it with and without the water pump. It's getting water, but, sure takes alot of pressure. Seems to want to bypass somewhere before the pump and come out by the prop.<br />Just making me wonder if somebody has removed something back in behind the prop. Maybe as a performance gain without realizing an adverse affect? <br />With the amount of water that seemed to be flowing out by the prop, I thought maybe it needed some backpressure at the exhaust or something of that sort that could only be supplied by lower unit submersion. <br />That seems to work (so far). <br />Just strikes me as odd that all the other boats I've had and friends (way too many)(boats, not friends).. all run on muffs just fine and it seems this one won't.