Stalling at low rpms

[Cptkid570]

Hey everyone,
1991 3.0 liter mercruiser, carbureted with electronic ignition, mechanical fuel pump. (I'm pretty sure it's a 1991 engine ? I bought it bobtail and put it in my 1987 boat a few years ago).

Anyway, the engine is stalling when it goes below 2000 rpms. Runs perfect about 2000 rpms. After it stalls, it's really hard to restart ? I have to spray starting fluid into the carb and after the engine fires up, I have to keep spraying it until the engine revs up.. then it runs good again (at the high rpms). So, I'm thinking that it's either getting too much gas and flooding or it's not getting enough gas and starving.

No lack of power and performs as usual when cruising around (at the higher rpm).

Only recent work that I've done on the boat (Before the problem started) it is that I was trying to diagnose the fuel gage not working properly and I removed the fuel sender. There was some corrosion around it, so I'm thinking that maybe some corrosion got into the gas. This is just a maybe, so I'm not completely relying in this in order to figure out what's wrong.

Only thing I've done is made sure it's getting spark.. but, when I tested for spark, it was at the higher rpm. I ran the boat around with some fuel treatment in it this weekend and it didn't make a difference.

Is it possible for a fuel pump to go bad and not provide enough gas at low rpms and work fine at high rpms?? Is it possible for a fuel filter to clog and work fine at high rpms, but not low?

I haven't checking into anything yet. So, anything is a possibility. I'm going to start with fuel filter since that is cheap and easy.

What do you guys think could be the problem?

 

[chiefalen]

Re: Stalling at low rpms

Carb rebuild, make sure you soak it and get every little hole CLEAN.

Then you can pressure test the pump 4-6 psi no more no less.

Then make sure when you have the carb off the screen in the fitting that goes into the carb is clean.

And if you have a screen inside the pump clean.

Fuel water separator clean filter, if you have one.

 

[ziggy]

Re: Stalling at low rpms

i'd think go to the adults only sticky at the top and read the fuel system test.
also might try running off a remote fuel tank see if that cures it.. running on a remote fuel tank will confirm that anything prior to the fuel pump is not suspect if it still acts the same way. if it cures it, confirms that the problem is prior to the fuel pump..
for sure on cleaning or replacing the fuel filters.
for sure check the fuel pump pressure too...
if all that fails, then i'd think it'd be time to perhaps check the carb...
if you didn't have a problem prior to inspecting your fuel sender in the fuel tank, and now you do, i'd think that'd be suspect as to a first place to look...

i agree it's probably a fuel issue since ya can spray some starting fluid into it to keep it running. i'd also not use starting fluid. i don't know what it's good for, but i don't think it's good for your engine..

 

[Cptkid570]

Re: Stalling at low rpms

If crap did get into the gas tank, shouldn't the fuel filter catch it?
I guess it's just a small screen on that fuel filter tube thing, but if something got past that, would it be large enough to mess up the carb?

 

[Bondo]

Re: Stalling at low rpms

If crap did get into the gas tank, shouldn't the fuel filter catch it?

Ayuh,.. Of course it will...

But it still has Nothing to do with the Fact that your Carb is AFU....
The low speed circuit in your carb is PLUGGED....

Rebuild, or replace the Carb,.... That's where the Problem is....

 

[chiefalen]

Re: Stalling at low rpms

^^^^^^^^^^^^^ What he said^^^^^^^^^^^^^^

 

[Cptkid570]

Re: Stalling at low rpms

Hey everyone.. just wanted to thank everyone for their replies and follow up on this. I had a spare carb for this motor (I'd replaced my motor a few years ago with a used motor that was complete & kept a lot of parts from my old motor)... Anyway, I bolted on the old carb and it worked perfectly... nothing wrong with the old carb when the old motor was pulled. I was worried that it wouldn't work because it's been sitting for a few years... but, it did.

I may try to rebuild the bad carb just so that I can get some experience at that. I hear it's not all that hard to rebuild 2 barrels (mercarb). But, we'll see.

 

[chiefalen]

Re: Stalling at low rpms

Yep the carb, rebuild the one thats bad take your time do it on a bench.

No distractions, have the kit there. And a big can of carb cleaner. Wal-mart has it.

Watch how the needle comes out.

They key is the real little holes. They have to be Clean.

Good luck !