1985 mercruiser 5.0 2bbl stalls out at lower R.P.M

[Henry78]

I have a 1985 Chris craft with a 200 h.p. mercruiser 5.0 2barel carb, and alpha 1 drive. The engine starts fine in nuetral, the problem I'm having is when I go to higher R.P.M (3000-3200+) and quickly cut back to nuetral position the engine stalls but will start back up. I checked the carb and cleaned it, replaced plugs and wires. Distributer cap and rotor look clean. Replaced fuel/water seperator filter and inline fuel filter at carb. After replacing all this the engine runs better but still stalls. Not to much of a carb guy, but looks to me like it might need rebuild. Any suggestions or Ideas of what might be causing this? Thanks Much!

 

[Fishermark]

Re: 1985 mercruiser 5.0 2bbl stalls out at lower R.P.M

Welcome aboard - time for a full tune up and perhaps carb rebuild. Do you have points ignition or electronic?

 

[Henry78]

Re: 1985 mercruiser 5.0 2bbl stalls out at lower R.P.M

I went and rebuild the carburator, And runs like a champ. Starts up and Idles fine and runs good at High R.P.M. I put the boat in water last evening to test run it. I cruised out to the center and went full throttle. Now I ran into another problem, now at high RPM about 15 sec on plane the engine starts cutting out until I lower the rpm it will keep running. Im thinking I might need to play with air/fuel screw. I set it at 1-1/4 turns out but ran a bit ruff and set 1-1/2. Not sure if thats correct. Also thinking about replacing fuel pump since I dont think has been replaced.

 

[wellcraft-classic210]

Re: 1985 mercruiser 5.0 2bbl stalls out at lower R.P.M

The screw I think yau are refering too is for the idle mixture. It is not in use over once your over 1000 rpms as the fuel is delivered through different passages & out of the venturis. Those are not adjustable with a screw.

It does sound like you are battling a feul delivery issue. Before you spend $ on a fuel pump you may want to do some verifications. Its more common that you could have a restriction in your lines, filter(s) or check valve. The tank vent needs to be clear as well.

Have you inspected the check valve in the barbed fitting coming off the fuel pickup in your tank?
How about the fuel filters -- are they new ?
Can you verfiy fuel pressure is present via a pressure gauge on the fuel line?

If those seem good you may want to rig up something temporary to watch the pressure under a heavy load while th problem occurs.
( be sure it does not leak for fire safety reasons ) If that does indicate low pressure -- but keep in mind any restrictions in the filter or lines can cause pump pressure to drop. If the pressure stay's high then that of course rules out fuel pressure. If th ppressure is normal most of the time / but drops under a heavy load & acceleration then its most likely a restriction.

Good luck

 

[Henry78]

Re: 1985 mercruiser 5.0 2bbl stalls out at lower R.P.M

The screw I think yau are refering too is for the idle mixture. It is not in use over once your over 1000 rpms as the fuel is delivered through different passages & out of the venturis. Those are not adjustable with a screw.

It does sound like you are battling a feul delivery issue. Before you spend $ on a fuel pump you may want to do some verifications. Its more common that you could have a restriction in your lines, filter(s) or check valve. The tank vent needs to be clear as well.

Have you inspected the check valve in the barbed fitting coming off the fuel pickup in your tank?
How about the fuel filters -- are they new ?
Can you verfiy fuel pressure is present via a pressure gauge on the fuel line?

If those seem good you may want to rig up something temporary to watch the pressure under a heavy load while th problem occurs.
( be sure it does not leak for fire safety reasons ) If that does indicate low pressure -- but keep in mind any restrictions in the filter or lines can cause pump pressure to drop. If the pressure stay high then that of course rules out fuel pressure.

Good luck

Yes that would be the idle mixer screw I mentioned. Both fuel filters were replaced. The one in the carb and the water/ fuel seperator. Didn't know there was a check valve by the tank. i will look into this. Thanks.