please help me get running again!!!

[aristocraft]

Ok so here it goes. I have a 1979 OMC 120. She has always run beautifully, and very smooth and fuel efficient. I love this little motor. So i will start from the beginning to give all the info i can.
we were cruising the lake one afternoon, and i typically cruise at 2600 RPM. it was running smooth, then just for a split second the rpms hesitated then picked right back up. it was unnoticeable almost. did this 3-4 times on the 15 minute ride. but made it home fine, and i thought almost nothing of it.
The next time we went out it started out hesitating much more this time, and got it up on cruise speed but the rpms kept jumping down the back up, watching the tach jump up and down. we started back for home when it started stumbling so bad i couldnt keep it on plane and barely running. then she died. I could get it to crank back up, but only for a second or two. and much to my dismay had to be towed back in.

So to this point, I have rebuilt the carb, twice. Replaced the coil, wires plugs. it has a newer mallory dist. in it. checked the points and they seemed to be sparking great. pulled the fuel line off the carb and it seems to be pumping great.

so on the hose in the drive way i can get it to crank up and it will run very roughly. rpms jumping up and down then eventually dies.

I consider myself pretty handy and I am needed any help i can get to get her going again. Please ask any questions that I may have left out. thank you for your time and help.
Scott

 

[Howard Sterndrive]

Re: please help me get running again!!!

points can't be "checked", you just have to change them
change the fuel filter
check or replace anti siphon valve at the tank

your symptoms also sound a bit like an engine with a failing manifold or riser gasket - letting water into the cylinders.

 

[aristocraft]

Re: please help me get running again!!!

Thanks for the help.

By checking the points I checked to see if they were sparking, and they were and to check the gap setting on them to make sure they were seperating and the contacting.
I changed the fuel filter and time of the carp rebuild number one, and it is pumping great. and yes replaced the filter in the carb inlet.

Anti siphon and vent valve to the tank and flowing fine... unfortunately.

 

[superbenk]

Re: please help me get running again!!!

You say fuel is flowing fine, but have you checked it with a pressure guage? You could still have a fuel problem somewhere.

 

[Howard Sterndrive]

Re: please help me get running again!!!

replaced the filter in the carb inlet.

does a 79 2.5 not also have the filter on the fuel pump?

 

[Howard Sterndrive]

Re: please help me get running again!!!

yeah it does according to the parts book. cut the safety wire, loosen the screw on top of that upside down bowl (can) on you fuel pump - there's a filter in there.

 

[1987larsoncitation]

Re: please help me get running again!!!

Have you checked the backflow valve in the exhaust manifold? Take out a plug and see if you have water in your cylinders.

 

[aristocraft]

Re: please help me get running again!!!

I do not seem to have water in the cylinders, pulled all plugs and check it out and it seems nice and dry in there.
My fuel pump has the big filter on the top of it under the dome. it has been replaced. after running it i can take the top half of the carburator off and the bowl is full of fuel. My original thought was it had to be fuel related because the way it was stumbling about, but cant seem to figure it!
no i have not check the fuel pressure, but if the bowl is full wouldnt it seem that the fuel system is fine?

Thanks to all for the help!!

 

[1987larsoncitation]

Try this..?

Try this..?

Have you checked the neutral safty switch? There is a little plunger that needs to fully extend(pop out). You will find it on the shift bracket that pivits between forward and reverse. Make sure the little arm on the switch fully returns when shifted. Sometimes they stick and you will get nothing.