1972 Mercruiser 888 Fueling Questions

[TheguyDirk]

1972 Sea ray with a ford 302/holley 2bbl carb. I recently had a tsp of gas in the sight glass of the fuel pump so I replaced the pump. After that it refused to start until I disconnected the boat tank and plumbed a line direct into a gas can. Started fairly easily from there and idled for 5min+ so I shut it down and replumbed the main boat tank. It started less easily but started and idled up to temp. Sounded sort of rough at idle and had a hard time maintaining 750-800rpm. Sounds okayer at 1000rpm. A week later I am attempting to start the boat again and it will crank but will not cough or try to start. If i give it gas directly through the butterfly choke itll kick and try to run. Not sure if im having an issue with the gas in the lines making its way back to the tank or if im having issues with my carb.
Previously with the fuel lines disconnected at the pump it could not build enough head pressure in the long run, or pulling air, to run. The jerry can length run is much shorter and can prime easier. Is there a check valve somewhere on these old tanks? Mine is in the nose of the boat and accessible not under the floor. I am able to hear air returning to the tank if I blow backwards into the line.
Im thinking it's pulling air from a cracked old line or something since if everything is sealed the fuel pump should retain vacuum on the line side. right?

 

[alldodge]

Is there a check valve somewhere on these old tanks?

Yes, it's called the antisiphon valve and all tanks are required to have one. Yours is probably gunked up. Barbed fitting on top of tank where rubber fuel line is connected

 

[TheguyDirk]

Thanks a ton for the confirmation! Im guessing those aren't marine specific? Sadly its the long weekend. I can pretty easily touch the top of the tank its gonna be fun to get up there.

 

[alldodge]

Their cheap enough and used on most all marine apps.
https://www.iboats.com/shop/catalogsearch/result/?q=anti+siphon+valve

 

[TheguyDirk]

Just updating there isn’t a check valve at the tank in these eras, or someone took it out but the line was very crusty. Replaced line up to where there seems to be pliable line and it’ll pull fuel and sorta run.

Runs like ****. Electric choke got hot like immediately and opened way up and after 15mins give or take no change. Mix screws do do something as I can over riches the ide but it is not great. Idle circuit maybe?

 

[kenny nunez]

If your Holley carburetor will not idle smooth with idle mixture screws 1.5 turns from lightly seated then you need to get the correct marine rebuild kit.
The idle stop screw should be 1-1.5 turns to be in the sweet spot.
Hopefully the suction tube in the tank is not cracked or perforated from age.

 

[Scott Danforth]

in addition to the anti siphon, many tank builders put a strainer filter in the pickup tube.

running rough at idle, however better above 1000 means the carb is full of crud (idle circuits are at bottom of fuel bowl and bottom of metering block

 

[TheguyDirk]

If your Holley carburetor will not idle smooth with idle mixture screws 1.5 turns from lightly seated then you need to get the correct marine rebuild kit.
The idle stop screw should be 1-1.5 turns to be in the sweet spot.
Hopefully the suction tube in the tank is not cracked or perforated from age.

When i reset them they were at 3/4 turn outwards. It does seem happiest (loose term) at 3/4-1 turns currently. The old line was just rubber tubing so it's not surprising that's hardened.
I did pull the distributor cap wondering if I had weak spark from there - did not check the point gap but it looks quite clean so I am thinking it is a dirty carb as well.

Last season it ran okay but would rough idle after being run medium/light for a day upon restarts. Also would have a tough time re-idling after a higher rpm cruise. Needed that 1k rpm or so again.