'71 1150 dies when cowling is on

[MercMan82]

1971 1150, while on muffs, idles fine with cowling off. When you put the cowling on and idle her up, she sputters and dies. Lakes are so low here right now I can't put in to do idle adjustments in gear. I opened up a little at a time til I hit half turn more on each carb. Does better but still wants to die at higher rpms with idle. Started at 1&1/2 turns from seated. Still too lean, or is there something else i should think of? This motor does not have a tach btw. Also, what's normal water pressure for this motor, and what would it be on the water hose? Getting a good steady stream, brand new impeller. Psi is about 1/2 psi at low idle and goes up to about 1&1/2 psi at say 1500 to 2000 rpms or so. Motor does not get hot btw. Thanks

 

[CharlieB]

Re: '71 1150 dies when cowling is on

On the hose, adjust idle mixture to 'Best' idle plus 1/4 turn. This should get you close enough to get started once on the water.

Dying once the covers are on is often one of two things, Restricted air inlet, rats, nest, bird nest, etc., Or an exhaust leak allowing fumes to be sucked back into the carbs.

Inspect all openings in the covers for restrictions, if none, then take a spray bottle, full it with a mixture of water and most any decent dish-washing liquid, about an inch and a half of soap then finish filling with water. Mix well. With the motor running , spray the soap along the edges of the exhaust plate, and the adapter plate to the mid-section. Watch carefully for any 'bubbles' forming, indicating exhaust gases leaking out.

 

[MercMan82]

Re: '71 1150 dies when cowling is on

All air inlets are good. Must be exhaust getting sucked back up. On the wrap around cowling, where is the main source of air, front, or top rear?. I'm thinking more than likely, I had the boat too close to the house so that I didn't get any wind to blow exhaust. It was backed up to the garage and the exhaust fumes were pretty heavy. I'll try out in the yard later and see what happens. Also, if it does leak around the mid section what would be the remedy other than pulling the power head and resealing it?

 

[Texasmark]

Re: '71 1150 dies when cowling is on

Most air inlets (that I have had/seen) are mounted high so that following seas won't enter the engine under rough water operating conditions.

 

[Chris1956]

Re: '71 1150 dies when cowling is on

The main air inlet is in the back of the top cowling, however, air does come in around the wrap cowling and thru the lower cowling as well. Exhaust leaks can be on the port side of the motor, or where the powerhead bolts to the midsection.

You really need to get that motor adjusted in the lake, with the cowling off. Observe for any smoke or exhaust noise. If you dont see any or hear any, it is likely no leak exists.