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OMC 120 Fuel Delivery Woes

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  • OMC 120 Fuel Delivery Woes

    OK so I just bought a project boat off a guy on Craigslist (go ahead and laugh now) and go figure, Im having trouble getting it running right.... Its a 1978 Beachcraft 17' runabout with an OMC 120 GM 153ci 2.5L inline 4 and Rochester 2bbl.

    When I showed up to view this boat the guy couldnt get it running, and I immediately noticed the loud clicking of an electric fuel pump. So I thought it was just a bad pump. The next day he borrowed a big diesel pump from a friend and brought it over to my house to show me the motor running. He hooked it up and the motor ran just fine, so I purchased the boat from him for 800 bucks. He told me that he had a friend rebuild the motor and there are less than 4 hours on it, but no receipts because it was a friend so.... anyways the exhaust manifold looks either new or painted, and the gaskets look fresh so he may... maybe... possibly... have been telling the truth.

    I took ownership and got to work on the fuel system. Now first off, I realize its unsafe to use an electric fuel pump without an oil pressure shutoff switch, but Im only troubleshooting here and it wont hit the water until the used oem carter mechanical fuel pump I ordered shows up in the mail... I got the existing fuel pump working by.... adding fuel to the tank! :-) but I still had a problem. It wouldnt start. It was flooded. So I pulled the fuse on the pump, got it started, and burned up the gas that was in the carb. Hooked up the pump and it ran for awhile, probably 20 minutes, then flooded again and died. Had to repeat the process to get it running again.

    I went out and bought a fuel pressure regulator, installed it between the pump and the carb, set it to 1psi, and the same problem occurs. It seems like there is just too much fuel being pushed into the carb somehow. Ive never worked on a carborated engine, and Im not a great mechanic, so this is all pretty new to me but Im a quick study. Friends have told me that it sounds like the float is stuck, and that I should rap on the carb to see if it becomes unstuck, but I dont even know where the float is on a carb.

    Also the idle seems off... I found that the little metal bar on the choke mechanism was just hanging there and not in the slot it was supposed to be sitting in, so I put it back in and tried adjusting it to make it idle better but it didnt seem to help. It was either too high, or it killed the engine... There are two screws on the bottom/front of the carb (if facing aft looking at the motor) and I wonder if those are adjustment screws? I tried spinning them a few rotations either direction and it didnt seem to adjust anything...

    Here are my questions:
    1. Where should I be tapping the carb (rochester) to attempt to free a stuck float?
    2. Is it safe to hose down the inside of the carb with carb cleaner to try to free up a stuck float?
    3. How do I adjust the idle (it seems a bit too high) and what is the appropriate rpm range at idle for this motor?
    4. Is it possible Im just chasing my tail and the oem mechaincal pump will solve these problems?

    Any help would be appreciated! And I'll upload pics of this project boat soon, and progress towards making it a decent fishing platform.

  • #2
    Re: OMC 120 Fuel Delivery Woes

    the float is inside the bowl, so you can't get to it with carb cleaner - like your friends said - just rap on it with a screwdriver handle - the bowl is the big chamber on the front or side of the carb where the fuel line is attached.
    Replace the mechanical fuel pump with an oem unit. That way you won't need any regulator and the fuel filter is on the pump, so right now you probably have no filter and might be pumping debris from the tank to the carb.
    How are you sure it is flooding? do you see black smoke? a stream of fuel into the carb?
    at 1 psi, I'd think it's stalling from lack of fuel, not too much fuel....
    Baba-buoy.

    Comment


    • #3
      Re: OMC 120 Fuel Delivery Woes

      Thanks Howard! I received the used oem mechanical omc carter pump in the mail today and promptly installed it, but I checked the oil and found its saturated with fuel... so I'll need to change the oil prior to starting it again. I think anyways, right? Id assume fuel in the oil is dangerous? That is an indicator of flooding right?

      No black smoke, but when I look at the little tubes at the top of the carb with the spark arrestor off they seemed to be pushing an aweful lot of fuel. Also prior to installing the regulator it was dripping fuel from all around the carb.

      I'll get the oil changed tomorrow and rap on the carb a bit as suggested, and let you know if it runs and idles the way it should!

      Oh do you know how many quarts are required for the OMC 120? Also Im assuming 10w30? Is it ok, or even recommended to use synthetic in a marine application?

      Comment


      • #4
        Re: OMC 120 Fuel Delivery Woes

        straight 30W, 20W50 or 25W40 for most climates. 10W30 too thin in my opinion. Synthetic a waste of money for oil that will see 50 hours of run time.
        5 quarts will usually do it.
        Baba-buoy.

        Comment


        • #5
          Re: OMC 120 Fuel Delivery Woes

          Update - Still havent been able to work on the boat due to the torrential downpours in WA this week... I think I'll back it into my garage tonight just to get it done. I need to change the oil to get all the fuel laden oil out of there and see if the new (to me) mechanical OMC fuel pump corrects the fuel delivery problem. If not it looks like Imma gonna learn how to rebuild a carb.... :-/

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          • #6
            Re: OMC 120 Fuel Delivery Woes

            Needle&seat prolly has dirt in and is not closing correctly. As for the fuel in oil,most likely the diaphragm in the fuel pump blew and kept running dumping fuel in crankcase.

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            • #7
              Re: OMC 120 Fuel Delivery Woes

              So I changed the oil today, got rid of all that fuel soaked oil, and got her running with the used mechanical pump. I have to say it looks much better. I no longer see massive amounts of fuel being dumped into the carb, but it still isnt running right. It was dark out when I ran the motor and I was using halogen work lamps, but Im pretty sure there was some white smoke from the exhaust. Does that indicate a rich fuel mixture? If so how do I adjust the rochester carb? Also it still idles too low, to the point where it diesels and dies. When looking at the carb, facing aft, there are two screws at the bottom of the carb. What do they do? One more question. If the needle+seat is dirty or stuck, can I use an additive like Berrymans B-12 Chemtool to clean it and get the gunk out of there? (http://www.oreillyauto.com/site/c/de...0407&ppt=C0126)

              Also, tomorrow I will be installing an Accell ignition coil. I checked all the wires and replaced all the plugs, and I saw spark on all of them, but I dont know if theres a way to ensure its a "good enough" spark, so its worth trying.

              Comment


              • #8
                Re: OMC 120 Fuel Delivery Woes

                So I watched a ton of youtube videos and learned how to adjust the idle air mixture, choke, and idle screw, and got the carb all tuned up... Good news! Motor is purring like a well fed kitten. All is well with the new (to me) mechanical fuel pump, but I have one potential problem. There is no return line fitting on the pump. Shouldnt there be a clear hose that goes from the fitting on the carb back to the pump?

                Comment


                • #9
                  Re: OMC 120 Fuel Delivery Woes

                  no return line = automotive pump
                  marine pumps have either a return line, or at least a glass reservoir to collect any leaking fuel should the diaphragm rupture
                  Baba-buoy.

                  Comment


                  • #10
                    Re: OMC 120 Fuel Delivery Woes

                    thats what I thought. It is painted the same color as the blue paint on the motor, and it looks to be original paint, as its worn off partially down to bare metal, and it is a carter, but I expected to see a hose fitting for the return line from the carb and it isnt there. It is quite large and I have seen the automotive counterpart. It looks different than the auto part from O'reilys. There is no glass bowl as far as I can tell, but perhaps the collection bowl your talking about is metal in this case? I'll take a picture shortly, or tomorrow in the daylight.

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                    • #11
                      Re: OMC 120 Fuel Delivery Woes

                      here's the 1978 120 fuel system. #79 is the glass bowl, but I don't understand the way it's drawn there. looks like its in the delivery line - but it can't be.
                      [IMG][/IMG]
                      Baba-buoy.

                      Comment


                      • #12
                        Re: OMC 120 Fuel Delivery Woes

                        here's the 1978 120 fuel system. #79 is the glass bowl, but I don't understand the way it's drawn there. looks like its in the delivery line - but it can't be.
                        Ayuh,... I believe it's for the ruptured diaphragm, as an indicator...

                        Comment


                        • #13
                          Re: OMC 120 Fuel Delivery Woes

                          Originally posted by Bond-o View Post
                          Ayuh,... I believe it's for the ruptured diaphragm, as an indicator...
                          Indeed it is sir. I looked at the fuel system on my 77 reinell omc 120 and it's all there. The glass bowl has a note inside that says, "if you see fuel here, replace fuel pump."

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                          • #14
                            Re: OMC 120 Fuel Delivery Woes

                            Originally posted by Howard Sterndrive View Post
                            here's the 1978 120 fuel system. #79 is the glass bowl, but I don't understand the way it's drawn there. looks like its in the delivery line - but it can't be.
                            [IMG][/IMG]
                            I know there are differences between the 77 and 78 models, but I'm wondering if the fuel pump changed at all? If not I got screwed by an ebay seller and they sold me a non marine pump.... Ill post some pics of my 77 reinell omc and my 78 beachcraft omc.

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                            • #15
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                              Re: OMC 120 Fuel Delivery Woes

                              Here is a pic of the fuel pump on my 77 Reinell OMC 120. The return line is located on the bottom of the pump, the IN side is the left and the OUT is the right of the pump. The glass bowl is in line with the return hose between the carb and the pump. The return hose connects on the carb at the same location as the empty fitting I'll show in the next pic. Forgive the watermark, I had to download a program to reduce the file size...

                              The way it SHOULD look... 77 Reinell 190 w/ OMC 120
                              Click image for larger version

Name:	Fuel pump side view 77 Reinell OMC 120 640x480.jpg
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ID:	7032776

                              This is the carb on the 78 Beachcraft OMC 120 that has no hose on the overflow fitting.
                              Click image for larger version

Name:	Overflow hose fitting on carb 78 Beachcraft OMC 120.jpg
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ID:	7032777Click image for larger version

Name:	Overflow hose fitting on carb 78 Beachcraft OMC 120 close up.jpg
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ID:	7032778

                              Heres the (automotive) fuel pump I got from some sheister on eBay, that is currently installed on the 78 Beachcraft OMC 120.
                              Click image for larger version

Name:	Fuel pump bottom view on 78 Beachcraft OMC 120.jpg
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ID:	7032779

                              And one more. I took a pic of the glass bowl on the 77 Reinell OMC 120, just in case anyone else has a similar issue in the future. Maybe this will help them.
                              Click image for larger version

Name:	Fuel pump glass bowl on 78 Reinell OMC 120.jpg
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ID:	7032780


                              So... what it comes down to is... I got screwed. Im off to look for another fuel pump. Unless anyone knows if I can tap a hole in the bottom of this fuel pump and add a fitting to run a hose from the carb?

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