how can i tell if i have a bad fuel pump

[bishop12]

1980 140 mercruiser, acts like its running out of fuel back off the throttle a bit and it picks back up for abou 10 seconds and does the same thing.Can I tell by taking off the fuel line at the carb and turning over the engine. If so how much fuel should be coming out of the line.

 

[CRT Skiff Crafter]

Re: how can i tell if i have a bad fuel pump

Hi Bishop12.<br /><br />Before you start on your fuel pump test, if you haven't already done so, remove the site hole screw in the float bowl (with the engine running) and check to ensure that your fuel level is just a tad below the bottom of the hole with no fuel actually getting out of the hole. If it's too low or too high, adjust the float level accordingly. If you can't get it adjusted, you probably have a needle and/or float issues. <br /><br />If there isn't any problem there, the basic pressure test procedure is to "T" a gauge (capable of reading low pressures) between the fuel pump and the carb. Most auto parts will carry these. NAPA will for sure. <br /><br />If you have a shop manual for you engine, there should be a specification for the proper pressure. <br /><br />There is also a flow test to determine if the pump is moving the appropriate volume of fuel. This entails pulling the line that feeds the carb and letting it empty into a quart size container (a canning jar is perfect). Remove the distributor secondary and run the starter (be sure to have water going to the stern drive). I don't know what the flow rate should be for your setup, but mine was a half quart in 30 seconds of cranking. There should also be a spec for this in your manual. <br /><br />Also, if your pump is equiped with a glass bowl, there should be a little sign in it that says something to the effective of " if you see fuel in this bowl, replace the pump". That's a great place to start because you may avoid all the testing. <br /><br />It so happens I just went through all of this within the last several weeks and interestingly the fuel pump was about the only thing that wasn't hosed on my engine!<br /><br />Good luck.<br />Regards, crt.

 

[bishop12]

Re: how can i tell if i have a bad fuel pump

Wow thats about the best advice ive got in a long time. I will try the fuel pump test tommorrow. Thanks I will keep you posted.

 

[CRT Skiff Crafter]

Re: how can i tell if i have a bad fuel pump

One more thing on this. <br /><br />Just to perhaps save some unnecessary effort on the pump tests, if you haven't already done so, remove the spark arrestor and make sure you don't have excessive fuel dumping down the carb into the manifold. Also look for fuel laying up on the butterfly area. If either of these conditions exist, it's probably not the fuel pump, but more likely carb issues, which would be covered by a complete carb rebuild. <br /><br />Again, good luck and keep us posted. <br /><br />Regards, crt.

 

[bishop12]

Re: how can i tell if i have a bad fuel pump

i have rebuilt the carb and it seems to respond the way it should,the only thing im not to sure about is the float level. It was leaking by the needle and I closed it off a bit and it stoped.Im not real sure about the carb having the screw for what you were talking about doing but im gonna check for it.If I turn it upside down, about how far do yo think the top of the float should be from the bottom of the top of the carb.

 

[CRT Skiff Crafter]

Re: how can i tell if i have a bad fuel pump

Float adjustment Depends on the type of carb. Example, for my Holley 2300 series 2bbl, the dry adjustment (meaning you've got it apart) is bowl inverted and needle adjusted till the float and bowl top (now the bottom due to inverting) are parallel. Other carb types require a different process, but if you've rebuilt yours, you know all of this already. <br /><br />If the needle was leaking, something is wrong. <br />Do you adjust your float level by loosening a locking screw and then turning the adjusting nut that the screw threads into? <br /><br />That other screw I mentioned: There should be a screw in the side body of the float bowl (probably opposite the side the throttle linkage is on) which allows you to actually see the fuel level in the bowl by removing the screw and peeking in the hole the screw was in. Then again, maybe your carb does not have this and I'm only serving to confuse you.<br /><br />Post what type of carb you have and I'll try to help more. I believe the positive thing so far is that since you had fuel leakage at the needle, it sounds like your problem may be a simple carb adjustment and not a fuel pump. <br /><br />Regards, crt.

 

[bishop12]

Re: how can i tell if i have a bad fuel pump

My carb is a rochester 2 jet. I didnt get to do any thing today,had to much rain.When I raise the float level any more I get the leaking thus causing my plugs to foul. I have tried 3 of these carbs and the same thing happend with all of them(leaking by the float).2 of the carbs I know were good I actually seen the run and not leak. I did pull the line off the carb to see just how much it was putting out and it was alot less than I had thought it should have done.Can these pumps be rebuilt.

 

[CRT Skiff Crafter]

Re: how can i tell if i have a bad fuel pump

Hi Bishop12.<br /><br />Well, your carb can't have the level externally adjusted, so my discussion about the site hole is not applicable.<br /><br />The float adjustment for your carb is accomplished by first measuring the distance from the top of the float to the air horn (if the float has a vertical seam) or measuring the distance from the lower edge of the float seam to the air horn (if the float has a horizontal seam) and comparing it to the specs. If an adjustment is required, you bend the float arm at the rear of the float to get the measurement correct. <br /><br />Late model fuel pumps can't be rebuilt. I'm not sure about yours specifically, but for my money I wouldn't even attempt it. They don't cost that much and it's just too dang risky in my opinion. <br /><br />If you want to do that flow test, your pump should put out a half a quart of fuel somewhere between 30 and 40 seconds, since the spec for a V8 is 20 seconds and for a 6cyl it's 30. Yours is a 4 cyl correct?<br /><br />I am not exactly certain about the pump pressure for your rig, but I'd guess if it's putting out 3.5 or better, it's good. <br /><br />Let me know how this goes. Again, I'll hang in here with ya as long as you find it helpful. <br /><br />regards, crt.

 

[bishop12]

Re: how can i tell if i have a bad fuel pump

Ok I checked out the fuel pump,and it was putting out as much if not more than what you had mentioned. I think im gonna see if I can find me another carb.Any one got one that they wanna sell pretty cheap. I will need a rochester 2 jet for a 140 mercruiser.

 

[CRT Skiff Crafter]

Re: how can i tell if i have a bad fuel pump

Hi Bishop12.<br /><br />Well, it's too bad that you have to spring for another carb. However, sometimes that's the easiest and best thing. <br /><br />Be sure and let us know how this evolves.<br /><br />Regards, crt.

 

[bishop12]

Re: how can i tell if i have a bad fuel pump

Hello again,I decided not to buy a carb just yet and to tinker a little more with mine. I found that it is not atomizing the fuel coming out of the venturies. But the fuel does atomize from the initial bust that the accelerator pump puts off.(just drips out) Any ideas.

 

[CRT Skiff Crafter]

Re: how can i tell if i have a bad fuel pump

Hi Bishop12. May be a power valve issue?<br /><br />Regards, crt