1978 mercury 800 fuel issues

[tbonebrad]

I have been having fuel problems with my motor since I bought it earlier this year so last month I rebuilt the fuel pump, rebuilt the carbs, bought a new fuel line and primer bulb, and put a clear glass filter on the fuel line so I could watch it and see whats happening. The first time I took the boat out after having done all this I ran MUCH better but still had a couple of issues getting it started.

My tilt and trim cylinders have been leaking so I just finished rebuilding those and was starting the motor up to make sure it was ready to go this weekend. I had a REALLY hard time getting it started. I was cranking on it forever before it finally started up and when it did start up it was only up for about 15 secs before it burned all the fuel in the carb bowls and died again. I took a video of the filter so you can see it draining the fuel then the filter fills up and the motor dies. Anyone have any idea where I go from here?


Heres the video1978 Mercury 800 Fuel Issues - YouTube

 

[tbonebrad]

Re: 1978 mercury 800 fuel issues

Do you guys think this is more of a fuel pump issue or carb issue?

 

[carholme]

Re: 1978 mercury 800 fuel issues

Try is again and when the fuel is just about used up and ready to die, start squeezing the bulb and if the engine keeps running you still have a problem with the fuel pump. The rationale for this is that if things are OK while you are squeezing the bulb, you have become the fuel pump.


Gerry

 

[tbonebrad]

Re: 1978 mercury 800 fuel issues

Yes this is exactly what is happening. So does this mean I should order another fuel pump rebuild kit? If I open the fuel pump back up is it going to ruin the new gaskets I put on it last month?

 

[Will Liston]

Re: 1978 mercury 800 fuel issues

It shouldn't just be careful and look for sticking after removing the bolts. I just rebuilt mine.

 

[Will Liston]

Re: 1978 mercury 800 fuel issues

And yes look at a parts diagram. See if your fuel diaphragm is in tact. You want to make sure there is no holes or cracks on it.

 

[tbonebrad]

Re: 1978 mercury 800 fuel issues

the kits are cheap, i guess i'll just buy another one in case. I'm wondering if there could have been junk in the fuel that is making a check valve stick or something.

 

[Ntatro]

Re: 1978 mercury 800 fuel issues

I have the same motor. I am having a fuel problem as well. The motor was running fine until I gave it full throttle and then it would cut out. Then it would only start and move a little bit before it would stall. Now it will not start at all. What are the odds that the main fuel line or bulb could be bad? I think my problem is the pump or main fuel hose. The bulb is very hard to squeeze. I am not sure if it is supposed to be easy or hard to squeeze. Any help would be appreciated. Do you know where a good place is to get the fuel pump rebuild kit.