Mercruiser 5.0 bogging down under load

[the docta]

Hi all

my first post but i have been following the forums for years.

my current set up is a 21ft british built offshore boat similar to a scarab 22 or small baja.

Motor is a late carb 5.0 merc v8 from early 2000s (its called a 5.0 alpha model). Electric fuel pump and 2bbl carb. Serviced recently with new oil and filter, plugs, leads, dizzy cap and fuel filter (spin on - only one it has i think).

I have a problem with motor running rough, however and am struggling to diagnose. Its ok on muffs and trolling but once opened afer a min or so it starts to miss and pop and witjin another min or so bogs right down coughing and spluttering verging on stall. If left ticking over / trolling it seems to clear itself after a few mins but as soon as i accellerate again within a few seconds it starts to deteriorate.

havent tried running off separate tank yet but figure it either fuel or ignition not mechanical as no signs of bigger issues.

Any thoughts based on above syptoms before i hook up to aux tank and throwing more parts at it (fuel pump, coil are obvious contenders). Tank breather seems fine so happy to discount that.

Thanks
Al

 

[Bondo]

havent tried running off separate tank yet

Ayuh,...... Welcome Aboard,..... I think this is the right direction, sure sounds like a lack of fuel flow,......

 

[superbenk]

Agree with Bond-o. I’d be suspecting the anti-siphon valve, pickup screen (in the tank), dirty carb.

 

[the docta]

Thanks guys. Fuel sounds like first port of call then.

 

[Maclin]

There may be a filter in the carb inlet. Good luck.

 

[the docta]

Thanks. Not sure if there is on this model but will go through fuel system and then look to have carb cleaned / rebuilt if needs be.