OMC 3 Liter Engine -Knocking sound coming & Fuel issue

[idesign]

Guys my original 1987 OMC engine block got cracked.I got older 1980 OMC 3 liter.Got engine block swapped.Engine is running good.When i am running at slow speed it is ok.But when i am trying to run faster like 10MPH+ i can hear some knocking or clicking sound coming from engine.I dont know if it is from piston or carburator or from somewhere else.Does any1 have any idea.
Also engine for running fine for few hour.But after that it suddenly started slowing .I dont really dont know how to explain.Like when ur about to to finish gas in car it acts crazy.Same things started in my boat and it stopped some times.When i give some choke and start it starts and after some time it runns wiredly and stops.My boat fuel tank was less then quarter left.Is it possible some dirt went in carburator and that is why it is doing like thing.Also i opened fuel pump uper cover for fuel filter and i dont see any fuel fiter installed.so is fuel filter necessary.Please let me know.thank you

Also can any1 tell me what type of engine oil it need.The manual for 1987 OMC says SAE-30.But mechanic told me SAE 30 dosent have detergent & gave me Merucry SAE 25W40 oil.So is it ok.let me know.thx

 

[sea wolf]

Re: OMC 3 Liter Engine -Knocking sound coming & Fuel issue

Yes, you need a fuel filter. When's the last time you gave it a complete tune-up? I don't know about the knocking sound, but it sure as hell ain't coming from the carb. We can't hear it so it's impossible to say. The mechanic that told you 30 wt. doesn't have detergents is full of sh*t. I've been using 30 wt. in my 3.0 for years.

 

[idesign]

Re: OMC 3 Liter Engine -Knocking sound coming & Fuel issue

Guys the koncking sound coming is very minimum.What i did is changed oil,filled with premium has and set the timing to 4degree according to manual.
Now engine is running good on slower speed.when i try to go faster like more then 15mph it goes but after sometime suddenlt it loses power and boat slows down.when i full throttle again it goes and does same thing after some time.so can any1 tell me what could be the problem.thank you

 

[sea wolf]

Re: OMC 3 Liter Engine -Knocking sound coming & Fuel issue

Is it knocking or pinging? What octane fuel are u using? You should be using 89 octane. What about a complete tuneup replacing points, plugs, filters? Ever cleaned the carb & flame arrester?

 

[mkast]

Re: OMC 3 Liter Engine -Knocking sound coming & Fuel issue

I got older 1980 OMC 3 liter.Got engine block swapped.

What kind of shape is this engine in? Did you record a build sheet on the engine?

 

[idesign]

Re: OMC 3 Liter Engine -Knocking sound coming & Fuel issue

What kind of shape is this engine in? Did you record a build sheet on the engine?

the engine shape is same as it was for 87 engine.i dont know anything about build sheet on the engine.where can i get that info.thx

 

[idesign]

Re: OMC 3 Liter Engine -Knocking sound coming & Fuel issue

Is it knocking or pinging? What octane fuel are u using? You should be using 89 octane. What about a complete tuneup replacing points, plugs, filters? Ever cleaned the carb & flame arrester?

i am sure best i can understand it is slow countinues knocking sound coming when i try to go on fast rpm.
I have put brand new sparkplug only,changed fuel pump fuel filter,cleaned flame arrester with wd-40..added some seafoam in fuel tank and on carburator from top.do i have to change plugs as it looks ok to me.
but how do i completely clean carb.do i have to whole carb apart and then clean.
on top of flame caburator it says "Use Octane 89 or HIgher Fuel".So i filled tank with premium octane 93 gas and set the timing to 4degree(that is according to manual).After this the knocing sound reduced.
please let me know what could be the problem.thank you

 

[sea wolf]

Re: OMC 3 Liter Engine -Knocking sound coming & Fuel issue

It's amost impossible for anyone to tell u what you are hearing from your description here. As far as rebuilding the carb, you need a shop manuel. It's too involved to get into here. And you should have also changed the points. What's the oil pressure?