1990 maxum 5.0 305 hp can't get 4200 rpms

[b54241_2000]

i have a maxum 5.0 v8 alpha one out drive i once could get 4200-4600 rpms but after 5 years now i cannot get the rpms. i have replaced the fuel filter and water seperator and put new plugs in the motor as well i put octane buster in the gas as well.i also replaced the coil but still cannot the rpms i had the prop re hubbed and cleaned as well and i still cannot get the rpms.can anyone point me in the right direction to try and figure out whats wrong?

 

[QC]

Re: 1990 maxum 5.0 305 hp can't get 4200 rpms

Take a look in the Adults only section ^^^^^^^. There could be a number of things causing your issue, but my first guess is weight gain. Also, if you consider buying octane booster again please just send me the money. I'll be happy, and you'll be no worse off . . . Octane is only about knock resistance, nothing else.

 

[JustJason]

Re: 1990 maxum 5.0 305 hp can't get 4200 rpms

you may have a fuel filter in the fuel pump, as well as another one in the carbs inlet... did you get both of those? You also said you replaced the plugs... how about the wires, cap and rotor to? All that should be done once a year anyways. Is your flame arrestor nice and clean?

 

[peanutbay1]

Re: 1990 maxum 5.0 305 hp can't get 4200 rpms

Check your timing advance mechanism under your points/condensor plate in the distributor. I have a 5.0 OMC and spent a ton of money and time for the exact same problem only to find out my timing advance mechanism was gunked up and needed cleaned/lubricated. I am not saying this is your problem for sure but my boat went from 4600rpms down to 4000rpms and after the fix I can pull 4800rpms if I want to. I would make sure all of your main tune up items are in good working order as well.

 

[180shabah]

Re: 1990 maxum 5.0 305 hp can't get 4200 rpms

There are no points in a 1990 mercruiser, but as mentioned cap rotor and wires should be replaced as part of the tune up. Also test the coil.

Last question - what did you expect the Octane Booster to do for you?

 

[b54241_2000]

Re: 1990 maxum 5.0 305 hp can't get 4200 rpms

i didn't think it will work for the problem that im now haveing i always put the buster in every boat i've ever owned at the start of ever seasons it helps with any problems that may accure down the the and this is the first time i've had any engine trouble.i just stated that in my question to yuo all because i wanted to let who ever would help me with this problem all the things i did prior to the problem