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  Montauk 17' setup , motor height, prop pitch ???

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Author Topic:   Montauk 17' setup , motor height, prop pitch ???
catherwood posted 12-26-2000 05:30 PM ET (US)   Profile for catherwood   Send Email to catherwood  
I am trying to set up my recently aquired 1985 Montauk 17' with 1988 Yamaha 90 (3 cyl).
The boat is standard layout, with the following: 26 gal gas tank under flip flop pilot seat, trolling motor battery mounted in front hatch, trolling motor mounted starboard bow. Problem I can only get 5200 rpm at WOT, trimmed out, and after just a few minutes of this I get the overheat horn, and the engine shuts down to idle.Yamaha spec says that I should be at 5500 at WOT. I can run all day at 4800rpm. I have changed out the overheat switch, no difference. When the engine shuts down, you can put your hand on the block, it isnt really not very hot.
Im running a 13.25 X 17 pitch alum. prop, motor cavitation plate is 1 1/2" above bottom of hull. Ive tried a 13.25 X 17 Stainless prop, and had the same results. The power head checks out, compression all within factory spec. Starts with a touch. Idles good. Comes up and on plane quick, seems to trim out right.Had the carbs rebuilt. The water impeller is new ( I put a whole new lower unit on ).Im reluctant to go to a 16 pitch prop, has anyone had to do that with a Montauk/90 hp??
Any body got a suggestion????? HELP!!
Barry posted 12-26-2000 11:00 PM ET (US)     Profile for Barry  Send Email to Barry     
Regarding only getting 5200 rpm, have you checked to see that when your throttle is fully advanced that the carbs are all the way open? I had this problem on my Mercury. A little adjustment gained me 400 rpm.

Otherwise I would think the prop pitch should be close. You could always try a 15".

triblet posted 12-27-2000 11:32 PM ET (US)     Profile for triblet  Send Email to triblet     
Throttles not opening all the way
wouldn't cause overheating.

Possible causes of overheating:

A. Lack of cooling water flow.
Could be an obstructions or the intakes
coming out of the water. Do you still
have a telltale stream at speed? Or bad
water pump (impeller, or much less likely,
the housing the impeller runs in). Or a
leak that causes the impeller to suck air
when you get on a plane.

B. Lean mixture. Hard to diagnose without
an exhaust gas analyzer. You may be
able to tell by warming up the engine,
putting in a fresh set of plugs, running
full throttle until it overheats, cutting
it clean, and pulling the plugs. The
collor should be an nice grey-tan color,
but I'm not sure you've got enough time
for deposits to build up.

Possible causes: carb problems (the
rebuild SHOULD have fixed this), clogged
fuel filter, clogged pickup on the fuel
tank (this will collapse the primer bulb),
loose quick disconnect, bad fuel pump.
One thing to try is to have a buddy pump
the primer bulb while you make a fast
run. That will help several of these
problems (been there).

C. Retarded spark (this is the one most folks
don't know about). Dunno how to chase
this one on an outboard, but first step
would be to check the idle timing.
You also may be able to check it with
the engine in a drum of water, and a
dummy load prop.

Chuck Tribolet

Clark Roberts posted 12-28-2000 08:02 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
check out thermostat! Also, I think the 90 Yam has a thermostat bypass (spring loaded blow-out valve) which should open at high speeds and completely by pass thermostat.. if this is malfunciononing it should be replaced... good luck troubleshooting... Clark
lhg posted 01-08-2001 02:36 AM ET (US)     Profile for lhg    
Are you sure it's not the oil injection warning horn. On my Mercs, if the horn is continuous, it's heat, if it beeps, it's oil.
Your description doesn't indicate an overheated engine, where you'd be getting a lot of steam.

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