Merc 4.3 Low Vacumn

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bigbill109

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I have a 1988 4.3 Mercuiser 175 hp. The problem is the engine keeps dying at idle. The timing is set @ 8 degrees bct. The book states it should be set at 800 rpm. When coming out of nuetral the rpm will drop before engaging the prop to about 700 rpm. Then as soon as the prop engages the engine dies. Vacumn gauge has been hooked up, the vacumn is about 15 in. at 800 rpm and drops to about 13 when idle drops. Cannot raise the vacumn with air fuel mixture screw. Replace plugs, wire, cap, rotator, rebuilt carb. and replaced the distributor with a 1989 distributor. Any help with this problem will be appreciated.
 
Reel Poor

Reel Poor

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Re: Merc 4.3 Low Vacumn

bigbill109 said:
When coming out of nuetral the rpm will drop before engaging the prop to about 700 rpm. Then as soon as the prop engages the engine dies.
Click to expand...

Is this happening on the hose or with the boat in the water?
 
Don S

Don S

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Re: Merc 4.3 Low Vacumn

Sounds a lot like the shift interrupt system is being engaged.
You might try disconnecting the shift interrupt switch on the engine and seeing if you can put it in gear and back out of gear if on the hose.
(NOTE: if boat is in the water, shut it off to get from in gear to neutral)
 
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bigbill109

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Re: Merc 4.3 Low Vacumn

It will do it on a hose but it worse when its in the water with a load
 
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bigbill109

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Re: Merc 4.3 Low Vacumn

Where is the shift interupt switch? and how do you adjust or do you replace?
 
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bigbill109

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Re: Merc 4.3 Low Vacumn

Not sure my reply went thru so here it is again, Where is the interrupt switch and how do you adjust or do you replace?
 
C

Coors

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Re: Merc 4.3 Low Vacumn

You need a manual; search in here, or some one will send a link.
 
Bondo

Bondo

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Re: Merc 4.3 Low Vacumn

Where is the interrupt switch and how do you adjust or do you replace?
Click to expand...

Ayuh,.....

It's on the Shift Plate where the forward,+ lower shaft cables come together.....

If the Shift Switch is activating,....
The Problem is Not the Switch, but the Lower Shift Cable needs to be Replaced........
 
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