470 runs fine at idle but stutters when throttled up

[Saber1111]

My 1981 Mercruiser 470 runs fine at idle and revs fine when in neutral or out of the water. When in gear in the water it won't go over 1000 RPm and stutters badly. I think its a fuel issue but I can't decide what to do next? I had the card rebuilt but don't know if it needs more attention or if the mechanical fuel pump should be changed. The fuel (from the tank to pump is clean). I changed the fuel filter and fuel lines, not obvious issue with either. There is a hard fuel line from the mechanical pump to the carb so I can't TEE a pressure gauge in there between to see if the pump is good. The clear hose which runs between the pump and the carb is new and only shows some discoloration at the lower end near pump. What is the likelyhood that it's a pump issue given that it idles fine but stutters with throttle applied?
Is there an easy wasy to test the pump, especially since the problem only happens with throttle applied and under load (in the water)?

Thanks.

 

[mr 88]

When is the last time you replaced and or checked your points ? I would not free rev a engine on muffs,ever.

 

[Saber1111]

It has electronic ignition. I did replace the plugs and will probably replace the distrib cap and wires but I don't see that being the cause of this issue....but I who knows.

 

[Saber1111]

It has electronic ignition. I did replace the plugs and will probably replace the distrib cap and wires but I don't see that being the cause of this issue....but who knows.

 

[alldodge]

My 1981 Mercruiser 470 runs fine at idle and revs fine when in neutral or out of the water. When in gear in the water it won't go over 1000 RPm and stutters badly. I think its a fuel issue but I can't decide what to do next? I had the card rebuilt but don't know if it needs more attention or if the mechanical fuel pump should be changed. The fuel (from the tank to pump is clean). I changed the fuel filter and fuel lines, not obvious issue with either. There is a hard fuel line from the mechanical pump to the carb so I can't TEE a pressure gauge in there between to see if the pump is good. The clear hose which runs between the pump and the carb is new and only shows some discoloration at the lower end near pump. What is the likelyhood that it's a pump issue given that it idles fine but stutters with throttle applied?
Is there an easy wasy to test the pump, especially since the problem only happens with throttle applied and under load (in the water)?

Thanks.

Yes you can. Either get two fittings and replace hard line with rubber line, or remove one end and attached rubber line with clamp to it. Put a tee on it and get a fitting to put on the other. Most all fittings can be found at your local hardware store.

I do see it as a fuel issue

 

[SDSeville]

get two fittings and replace hard line with rubber line...

+1. That's what I did. It was super easy and allowed me to use the cheap inline pressure gauge from the auto parts store. Reinstalled the metal fuel line once my fuel issues were resolved.