Merc 470 sluggish when engine under load

[thenthfce1978]

I have a 78 Mercruiser 470, 3.7L 165Hp 224cubic inch I/O. I am able to go slightly above idle without an issue, problem now is that once I push the throttle down, give it some gas the engine wants to die. This boat sat unused for 6 years, with a gallon or 2 of old gas in it. I diluted my old gas with another 15 gallons of new, but still arent getting better response from the engine. I have a feeling its my fuel filter. Do you agree? If so where is my filter? Is it easy to change? How do I change it? Any help is always greatly appreciated.

 

[DJP]

Re: Merc 470 sluggish when engine under load

I assume the boat sat outside, if so then yes you probably do have a fuel restriction. The fuel filter should be in-line either close to the carburator or a screw on type located on an inner engine compartment wall, the latter of which seems unlikely. The carburator may also be seriously gummed up with varnish / gasoline residue, if that's the case then I'm surprised you got it to run at all. I would suggest you remove the carb and accordingly dis-assemble it and clean it. However if the varnish is so heavy that cleaning is a waste of time then replacement is necessary. However be mindful that if infact there is varnish in the carb then it is also throughout the fuel delivery system, and the problem won't go away until it (the varnish) is completely gone. Good Luck

 

[MrBill]

Re: Merc 470 sluggish when engine under load

Trippin identifies good points and potentially what you're up against...but do the easy stuff first. My 3.7L has an in-line fuel filter (actually only a screen) that's easily replaceable, for $2 and 15 minutes of time it's worth replacing. Be VERY CAREFULL when replacing not to 'twist crimp the aluminum fuel line and don't use teflon pipe tape on the threads, use the correct pipe dope, Loctite or otherwise. Next clean the spark arrestor with carb cleaner, also liberally spray-clean the carb insides. Also, I would try a fuel additive, something like what should have been used to winterize. Then run the engine for 30-45 minutes...for $10-12 you'll probably improve engine performance, if so you'll know that you're headed in the right direction.

 

[chiefmike58]

Re: Merc 470 sluggish when engine under load

If the fuel filter doesn't do it for you, try a new accelerator pump, located inside carb.