possible coil or fuel pump problem

The issue we are having is. The boat is a1984 mercruiser 120 and it will start all the time with just a tap of the key and run great up to 3700 rpm but when i push it to even 3800 or more it will start to surg and the die off but if i pull the throttle back to 3700 it will even out and run great until i push it again. I did notice that when i take it over the 3700 it will run great but only for a few minutes and that time will get shorter the longer we run the boat. Im not sure if its fuel pump or coil or ??? . I did check the clear tube on the pump and its dry. Any opinions

Re: possible coil or fuel pump problem

rpatton said:

The issue we are having is. The boat is a1984 mercruiser 120 and it will start all the time with just a tap of the key and run great up to 3700 rpm but when i push it to even 3800 or more it will start to surg and the die off but if i pull the throttle back to 3700 it will even out and run great until i push it again. I did notice that when i take it over the 3700 it will run great but only for a few minutes and that time will get shorter the longer we run the boat. Im not sure if its fuel pump or coil or ??? . I did check the clear tube on the pump and its dry. Any opinions

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Sounds like a fuel problem. I'd first run the boat on an outboard portable fuel tank to eliminate fuel pickup/anti syphon/bad fuel line possibilities.

Re: possible coil or fuel pump problem

Thanks for the repley. I thought fuel to at first until when i went to pull the pump off and it seemed to have a lot of presure and fuel in the line. Thats when i started thinking the coil might be heating up and cutting out at wot. This idea i got from doing a search on the forum. Does anyone know of a way to test a coil for my problem

Re: possible coil or fuel pump problem

rpatton said:

Thanks for the repley. I thought fuel to at first until when i went to pull the pump off and it seemed to have a lot of presure and fuel in the line. Thats when i started thinking the coil might be heating up and cutting out at wot. This idea i got from doing a search on the forum. Does anyone know of a way to test a coil for my problem

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Got to find someone with a coil tester or sub in a known good one for that.

You don't know that there is fuel pressure in that line at 3800 rpm unless you run it with a gauge. If you idle in and then pull the line of course there is pressure there as the boat runs well at those speeds.

If it was at my shop I'd still be looking at fuel, if pressure ok check filter in carb inlet and float height and also needle and seat for obstruction, any of these could cause similar problems. Of course I've been wrong before.

Re: possible coil or fuel pump problem

Yea your right idleing back to the slip would give me a false reading. When im back down at the boat next weekend ill try the gas can thing. Do you think i can rule out the pump since there is no sighn of fuel in the clear line to the carb. Its possible i have a carb issue but i dont think so . If it where carb would it not do it all the time. Mine will run flat out for about 5-10 minutes then it will surge. Then if i pull back and it acts like it catchws up it will go flat out again but only for a little less time then the first and so on . I can beleve its fuel since that what i first thought to. I even opened the fill cap in case the vent was pluged but no help. If it was in your shop what exactly would you do.