72' 7.5HP need to test fuel pump

[mscher]

looking for a quick way for testing fuel pump.

 

[racerone]

Operate the manual pump on the hose and report what happens then.---------Does the motor keep running ?---Does the motor still run the same then ?-------Does the motor run better ?----------And what is your motor doing / not doing now that leads you to believe there is a pump issue.

 

[mscher]

Operate the manual pump on the hose and report what happens then.---------Does the motor keep running ?---Does the motor still run the same then ?-------Does the motor run better ?----------And what is your motor doing / not doing now that leads you to believe there is a pump issue.

Thanks for the repsonse. It really does not seem to make much difference. the carb appears to be getting flooded, also. I removed (temporarily) the shift/throttle restrictor and putting the throttle to 3/4 fast and it starts right up, but obviously it can't take the high revs, so when I slow it down, it just dies. the plugs are really wet also.
I have had the carb apart twice and cleaned, seemed pretty clean inside. It been the same problem all along. I did have it idling pretty good, for about 5 minutes, or so recently.

maybe a carb float issues?

 

[tpenfield]

The fuel pump is pretty simple . . . a couple of check valves and a diaphragm. I have a thread here on iBoats about re-building the pump on my 1969 Merc 7.5

http://forums.iboats.com/forum/engi...r-outboards/644827-1969-mercury-7-5-fuel-pump

 

[mscher]

I did some experimentation, and I think the fuel pump is ok and maybe located the problem area (or at least indication), hopefully that can be fixed.

Was wondering if the float valve was malfunctioning, the fuel pump would be flooding the carb. I tested by disconnecting the cap where the fuel filter is and put the incoming fuel line in a collection cup. I pulled the engine start rope it did pretty much the same thing, not starting unless the throttle was on fast. In the mean time, a fair amount of fuel spurted out of the line from the fuel pump, into the collection cup.

I'm assuming that the engine can run without the fuel pump, as long at there is fuel in the float bowl. Is this correct? I don't want to be testing in a way that won't work any way.

Anyway, here is where I am.

The carb always has been wet in the throat and a little puddle underneath, on the motor frame. maybe it was doing this all along, but now I notice fuel dripping off the end, of the shaft for the throttle shutter.

Will look to see where the fuel is coming from

 

[tpenfield]

The carbs on these small engines are fairly primitive, so don't be too alarmed by flooding. My Merc and johnson both tend to flood if they don't start up within a few pulls.

As long as you have fuel in the bowl the engine will try to run.

If I recall correctly, the Merc carb had a mixture screw (or two) to adjust the fuel mixture. Had you tried adjusting those to see if you get a normal operation.

 

[mscher]

Yes I did try to adjust the mixture, since initially ( i had discovered), the idle adjustment screw was turned way out. It seemed to help for a bit but then want back to the usual problem. It looks like the extra fuel might be coming down through the idle limiter, which might have a smashed copper gasket (or not gasket). I have received a carb rebuild/gasket kit, which I'm going to install tomorrow.

 

[Silvertip]

For excess fuel to get into the engine causing running problems the inlet needle and seat need to be assembled and operating properly. The float also needs to be able to actually "float" and it's height properly adjusted. Just messing with adjustment screws not knowing whether they were ever correctly set is a bad way to approach carburetor issues.

 

[mscher]

For excess fuel to get into the engine causing running problems the inlet needle and seat need to be assembled and operating properly. The float also needs to be able to actually "float" and it's height properly adjusted. Just messing with adjustment screws not knowing whether they were ever correctly set is a bad way to approach carburetor issues.

The float had been tested and adjusted. The idle mixture needle, was put back to the initial adjustment, by procedures from the manual. I'm not a marine mechanic, but an idle screw, turned out about six turns seemed a bit much.

Otherwise, i don't have much choice, other than to "mess" with it. It's puddling fuel underneath and will only start and run on high throttle.

 

[mscher]

Rebuilt carb, no changes.

Reading up on this, I'm learning ( I think) that the idle is actually set and controlled by the engine timing, not the carb itself.

can anyone elaborate?