Mercruiser 888 Fuel System Questions

[ctanke]

Greetings wise ones’

I have a very nice running ‘72 Mercruiser 888/Ford 302.
I’m using 93 octane religiously adding Stable Marine at every top off and an occasional Sea Foam additive treatment as well to counteract some of the Ethanol. Had the boat 6 Years and am having to rebuild the carb now a third time. Here’s my questions

1. How often do these old Hollys need to be rebuilt?

2. This system utilized a glass bowl sediment filter along with a separate canister water separation filter. I’m remote from the boat right now but was wondering do you know if there should be a paper filter within the sediment bowl? Just hit me that I’ve never seen one in there

3. Can you foresee any issues if I were to add an inline filter to this system between the tank and the sediment bowl? I’m OK if this would be overkill - but want to be sure it wouldn’t impede any necessary fuel flow or pressure if I purchased the correct one.

Thanks in advance

CT

 

[alldodge]

Your spending why to much money on fuel buying 93, and your getting less power out of the motor for it.

No comment on your addatives

Glass bowl filter should not be on a boat, change to metal canister if you can

Check where your getting your fuel, might be a problem, or may be time to clean your tank

In any case you need a better filter because stuff is getting past it. Carbs should not need to be clean that often

 

[kenny nunez]

Is the sediment bowl screwed into the side of the fuel pump? If it is then it is there to indicate that the fuel pump gas a ruptured diaphragm. Holley carburetors usually need rebuilding because the metering block gaskets shrink and some of the passages get blocked.
try to post a picture of the bowl in question.

 

[Scott Danforth]

agree, anything more than 89 octane is a waste

if you rebuild the carb, the blue gaskets will allow you to pull the bowls off many many many times without needing new gaskets

usually a holley needs a rebuild when there is lots of crud sediment in the bottom of the bowl that plugs the idle circuits, or with the age you have, if you get a back-fire, you would rupture the power valve. there is a power valve saver kit which has a steel check valve you add to the carb base.

find where your crud is coming from. it may be the pile of additives you are using or you are not boating often enough.

if the sediment looks like rust, you may have a metal tank that is rusting.

 

[ctanke]

Thanks for the comebacks guys

The glass bowl apparatus is original to the boat. Does that change your thoughts?

Love to run 89 octane as I can get that grade in Ethanol free!
Mercruiser called for higher than that in 1972. What are the downsides for running lesser octane? Would the timing need to be advanced to accommodate this?

Tank is 48 years old - I’m going to replace it with a poli tank
please advise

 

[ctanke]

Regarding the filter, are Sierra water sep filters considered good quality? I believe I was using their 10 micron version

 

[alldodge]

Mercruiser called for higher than that in 1972.

You are correct manual 1 shows 93 Octane required, but still only 8.5:1 compression at 10 BTDC

According to what I'm finding your motor came with a canister filter
https://www.mercruiserparts.com/bam/subassembly/31949/1580/50

Sierra or Merc filters is no issue

 

[ctanke]

Hey alldodge

Yes it has the canister screw in but also has the glass bowl apparatus below it ( but not connected). Weird?

Could you put in layman terms the 8.5/1 compression advice. I’m not familiar with this.

Really good looking but not that bright (LOL)

 

[alldodge]

Back in 72 many things were different. They used Research method and leaded gas. Many years later they started using R + M / 2

Research method (RON) + Motor method (MON)

Not a chem expert, just saying things changed, and the 8.5 compression ratio is not that high. Hey Scott Danforth what you think?

 

[Scott Danforth]

your motor needs 93 octane RON which is about 85 octane for the (R+M)/2 current standard today

with 8.5:1, you could bump your base timing to 14BTDC and still run 87 pump gas

the bigger issue is are you running a lead additive in your pre 1974 motor or do you smoke a bit?

 

[ctanke]

Hey fellas

I don’t add lead and have not noticed a smoking issue
Please advise on this

If I wanted to burn non-ethanol 89 octane what would be a starting point for my base timing # or BTDC?