2 barrel marine carb, no accelerator pump? 75 351w

Hi all.. So pulled carburetor on motor, it's 2 barrel rochester.. I can't seem to locate the passage under the accelerator plunger, on quadrajets theres usually a small ball bearing that blocks fuel flow back into float chamber..

Mine just looks blocked. The small recess outside plunger housing also seems undrilled. I would assume this is a safety feature or am I missing something?

Surely the plunger needs to draw fuel in before squirting it up into carb?

The outgoing passage is there but for the life of me cannot find the supplying hole...

??

The ball bearing and spring are in a different location on a 2 bbl

see picture.

There must be a clear path for fuel to this discharge ports, (accelerator pump circuit) so make sure you find the port at the acc pump and it is clear to the discharge port.

The discharge port has a T shaped brass piece and the carb body is "pinched" to keep it in place. The T fits into the spring.

Use a good set of needle nose pliers and pull the T out.
The kit should have all new hardware.

When re installing use a small screw driver or punch to re "pinch" the body to keep it in place. Only enough to hold it.!!

Also there are different carbs used. Early models had the spring and ball, later models did not.

It looks to me like the fuel just dumps into the chamber when the plunger is all the way up that is the slot on the side of the chamber? I could be wrong but thats my guess.

Yep, the fuel enters via the slot in the side with the "cup" seal on the end of the plunger acting as a valve. Lets fuel pass on the upstroke, and not on the down.

fantastic guys thanks! esp kghost, i quickly paged thru a mercruiser manual and found a 2 barrel carb diagram with the check ball in the plunger hole and thats what threw me off.. yes i did pull the spring and check ball from the hole, just never saw such a design.

Muchos thanks..

Now on a 2nd note - im considering a 4 barrel upgrade - im quite familiar with quadrajets and LOVE the primary performance on the small barrels.. been reading there werent too many spreadbore manifolds for the 351w's - considering a trip to junk yard to get a stock iron squarebore -

Im not too worried about a spread to square adapter - adding height does add velocity. I might even throw in a 1" spacer too -

So any thoughts about a qjet spread vs a squarebore holley 600cfm on this motor?


Spent 2 days beating on a seized starter bolt and FINALLY got starter out which I will rebuild - block casting # is D4AE-6015-AA-8 as far as i can make out from upside down pics -

If you can only find a square bore 4bbl manifold then go with a marine holley. You will need to adapt the linkage mount though..... I have done it befor. takes a little creative thinking and "hacking".

Mercruiser did use holley's so the linkage may be available to purchase.

No need for a 1 inch spacer........again low rpm torque is the quest not high rpm power.

https://www.summitracing.com/parts/...ovNyh30EF_WH9Z8qYeOAd8onHCUzuvdMrnhoCvwPw_wcB


This site sells the cable bracket for holley applications............Item 17

https://www.marineengine.com/parts/...-4166999/fuel-pump-fuel-filter-and-carburetor

hi thanks for that - I have read aluminium on salt water is a no-no - not 100% familiar what cooling system I have but im sure its raw.. two big steel risers on exhaust ports and hoses that look as if they feed from/to rear of the boat -

Also that intake is for a chevy.. mines a 351w.. Looking at buying a marine quadrajet but will check other brands too.. holley seems a good choice- sad that i have the perfect 4 barrel holley 4160 carb up in seattle off a 351! and down in LA now -

The way to tell if "fresh" vs "raw water" is the presence of a heat exchanger, i.e., a tank (front or rear of engine, if in front sometimes vertical with a "radiator" cap on it). "fresh" is a misnomer and really means that the block (at least) and often the manifolds (but never the risers) are cooled by a 50/50 mix of fresh water and antifreeze. In a "raw" water cooled engine, the whole shebang is directly cooled by what ever water the boat is floating in. In the final analysis, the cooling is provided by the water the boat is floating in for "fresh water" systems via the heat exchanger, a "radiator" that is a water to water exchanger instead of water to air as in a car/truck...etc. Presence of "big steel risers" is not indicative. Some commercial/work boats use "dry stack" but that is another story completely.

thanks sandkicker, yes no tank so its raw.. I saw a guy poking around his with a pick - is there a way to try descale these things? Also - waiting for new starter to be delivered today - is there a way to tell the condition of the heat risers?

Trying to find out of the sierra rebuilt marine starter is reduction or not - id def prefer a pmgr type replacement if possible..

Get a couple gallons of salt-away and put the drive in a large storage container or water trough and fill it with water and pour the saltaway in then just run it for at least 1/2 hour in the tub. If it has a oil cooler in it just replace the cooler if you do not know how old it is. Either engine oil or power steering cooler are regular maintenance items and cannot be cleaned properly.

great - well the engine oil is still yellow unbelievably. This thing has done 40 hours since it was rebuilt - i trust the PO completely, despite that Im always double checking the "workmanship" either way.. getting stuck on the highway is one thing.. the sea is a complete different story.

Picked up my new pmgr starter today so looking forward to getting the motor running 2moro. tx for the salt away tip - will see if i can find some along with a large tub

A "warning" about salt away... it foams. After it runs for half an hour, let it sit for another half hour and then flush with plain water. If very cruddy, you may have to replace the salt away. Dilute per package instructions.

I don't know of any way to tell if "heat risers" ( I assume you mean exhaust elbows) are ok. some folks say to pressure test them. My problem with this is that these are really a "wear" item as every year some more wall rusts away. there is just a relatively thin wall between the hot exhaust gas on one side and typically 140 degree sea water on the other side. I got 9 seasons of light use out of a set of "dry joint" MERC OEM elbows by regular flushing with salt away. They were still OK when I pulled them, but the cost of a pair of new elbows verses what could be a whole engine not a bet I like to take.

Re: still yellow oil. Is it any "better", or just as yellow. It can take several oil changes to clear it since it's difficult to get all of the old crap out. Had a Volvo 4 banger get water in via the dip stick once and as I recall I changed the oil 6 times....(and eventually the starter)... and that engine had a bottom of the oil pan drain.

tx cap bob - well trying to get the motor running today. An old sun tune kit also on the way- hoping to monitor the gauges once shes had a few heat cycles and keep a pretty good eye on her.

Thinking of installing a separate heat alarm that is loud enough to alert me underway if anything gets too hot.. what would be a good temp - like 240? soon as it reaches that I can at least shut down and inspect.

Also - is it possible to upgrade from raw to closed?

Over temp should be 190ish and 200 max.

Once you reach 220 and up you take a chance on head gasket and head surface damage.

Merc uses temp switches on most late 90's models.............

You will need a temp switch, one that mounts directly into the manifold water path, a loud alarm. and wire.

The temp switch is the ground path for the alarm. When the switch is made it is a short to ground. So to teat alarm simply ground wire.

gr8 kg thanks.. once shes up and running ill do exactly that I think ill install two alarms - one for backup!