75HP Mercury will not idle

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vaboatdoc

Cadet
Joined
Dec 29, 2007
Messages
21
Heres a great one. 1999ish (not totally sure on year) model 75HP mercury carbs have been rebuilt fuel pump rebuilt checked reed valves checked idle timing and wot timing all good did sync and link and all that good mess new plugs and checked compression and spark all are good. But engine will still not idle. Put it in fast idle and it does good but no idle at all. Please help if possible
 
Barnacle_Bill

Barnacle_Bill

Admiral
Joined
Feb 8, 2004
Messages
6,469
Re: 75HP Mercury will not idle

When you rebuilt the fuel pump did you install the new style check valves?
 
V

vaboatdoc

Cadet
Joined
Dec 29, 2007
Messages
21
Re: 75HP Mercury will not idle

finally got it figured..key switch had shorted and choke was sticking open and flooding it at idle
 
I

imported_Voyager

Seaman Apprentice
Joined
Feb 8, 2007
Messages
36
Re: 75HP Mercury will not idle

bhile said:
When you rebuilt the fuel pump did you install the new style check valves?
Click to expand...

What are the "new style" check valves? My m50 (in-line 4 cyl., 50hp, 1982, "blue band", #6223380) has what I think is a fuel pump issue. The gasket that has the reed valves for the pump is black rubber (from mercury). When I rebuilt the carbs, I took out gaskets that were a tan plastic with some reinforcement in it. Did I toss "new style" valves and install old style, and if so, who sells the new style?

I now have idle issues that come and go. Motor idles fine while tilted up to negotiate shallows, dies when tilted back down. I suspect that it isn't pumping fuel well at idle, sometimes the hole shot is weak too...
 
Barnacle_Bill

Barnacle_Bill

Admiral
Joined
Feb 8, 2004
Messages
6,469
Re: 75HP Mercury will not idle

imported_Voyager said:
What are the "new style" check valves? My m50 (in-line 4 cyl., 50hp, 1982, "blue band", #6223380) has what I think is a fuel pump issue. The gasket that has the reed valves for the pump is black rubber (from mercury). When I rebuilt the carbs, I took out gaskets that were a tan plastic with some reinforcement in it. Did I toss "new style" valves and install old style, and if so, who sells the new style?

I now have idle issues that come and go. Motor idles fine while tilted up to negotiate shallows, dies when tilted back down. I suspect that it isn't pumping fuel well at idle, sometimes the hole shot is weak too...
Click to expand...

There use to be a site that listed Merc TSBs but Merc made them take them down. I guess Merc doesn't want us to know what's wrong with their motors. I don't remember what all years it covered but what they were having you do is replace the rubber type check valves with plastic ones. The new ones come with the fuel pump kit that you can get from the dealer and it includes an explanation.
 
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