4 hp Mercury wont run!!!!!!

[Ivan Y]

I've got a 1979 Mercury 4hp that will fire 1st or 2nd pull with the choke on. Once it fires it wont run with the choke in or out. <br />It will run fairly well with the choke closed (off) about 7/8ths of the way. It seems like its running out of gas with the choke open and obviously not getting enough air with it closed (on).<br />Whats really weird about it is that the first time I ran it, it idled and ran like a champ, now its turned goofy on me.<br /><br />Is it sucking air??? Is something plugged???(I have no clue as to where a fuel filter is on this motor) or do I look at something else??? Thanks in advance.<br /><br />Ivan

 

[Laddies]

Re: 4 hp Mercury wont run!!!!!!

you need to clean the carb.

 

[Byteme]

Re: 4 hp Mercury wont run!!!!!!

I had one that I thought the carb was gummed up pretty bad as well. <br />The thing is, I forgot something very simple. The slow speed idle adjusting screw was so far out of wack from where it was supposed to be I just assumed there was no adjustment to be had. I screwed it all the way back in and then back out to where it purred like a kitten. <br />Most likey not going to help you, but this saved me a whole lot of extra work not overlooking the obvious.

 

[Paul Moir]

Re: 4 hp Mercury wont run!!!!!!

This is the 2 cylinder model right?<br /><br />If you've got a gravity-fed one with the built in tank, then the filter is supposed to be on the fitting on the tank. Unscrew it from the tank to 'find' it. Like a lot of parts on that O/B, the filter is NLA and may be missing. I ended up mounting a large in-line one in the cavity underneath the carb.<br /><br />My thoughts are with laddiesservice on that one. Though you can try this quick and dirty fix on that particular model. Completely unscrew the lean adjustment knob and spray carb cleaner in through there. This gives you direct access to the narrowest constriction: the idle oriface. Once clean, turn the idle screw back in till it lightly seats, and then back out 1-1/2 turns from there. Warm up the engine and adjust it in till you get the best running. In gear, accelerate quickly. If the engine hesitates, richen the idle mix a little more.<br />(I must have 'fixed' the Gnat I'm familiar with 4 times this way before figuring out the fuel filter was missing!)<br />If you're going to tinker on that engine, a manual is a must. Just changing the idle rpms is a challange!