Mercarb 2BBL accelerator pump check ball

[IanFS]

Hi all, I hope you are all well.
I'm rebuilding my Mercarb serial number 3304 9565 model year 7Y 03.
I've been searching through the Mercruiser service manual and made a lot of internet searches including a search through the forum, but I can't find a definitive answer for what the aluminium check ball (provided in the kit) actually does or in fact whether it is necessary.
The Manual and Schematic provided in the kit shows the check ball but one source said it was only their on earlier models as a check to stop the piston bottoming out. Others say its something to do with fuel return to the bowl.
Could someone provide me with a definitive answer please? To check ball or not to check ball, that is the question? And what does it do?
Thank you chaps.
Ian

 

[alldodge]

The check ball is used in the accelerator pump circuit. It allows fuel to be sucked in, because without it the pump would be pushing fuel back n forth with no pressure. The gif below is for the 2GC and note how if works

 

[IanFS]

Thanks alldodge, but sadly that looks nothing like the Mercarb accelerator pump assembly. The reference to the check ball in the gif is an obvious one, but the Mercarb doesn't have a place for it, unless it just floats around in the pump chamber. There is a hole and a slot in the chamber but the hole wouldn't hold the ball and the slot is too big for the ball it would float through. I've added some photos........ and I'm still puzzled or just plain stupid, not sure which.

 

[CaptnKingfisher]

The check ball is used in the accelerator pump circuit. It allows fuel to be sucked in, because without it the pump would be pushing fuel back n forth with no pressure. The gif below is for the 2GC and note how if works

View attachment 347239

Where did you get this gif? I'm trying to learn more about carberators

 

[alldodge]

TanFS I know itrs not the Merc carb its the 2GC and is just there to see how one carb uses the check ball. With yours when the pump is moves down the check ball is under a spring and that keeps the pump from sucking air.



Note the slot in the pump cylinder. This is where the pump gets fuel

 

[alldodge]

The check ball also stops the motor from sucking fuel out of the carb bowl when running

 

[IanFS]

Thanks alldodge, but I am not asking about the stainless steel check ball which is installed under the spring and secured by the T bar, situated under the Venturi assembly, which I have installed successfully.
I am asking whether the aluminium check ball should be used and what is it for, which according to the schematic in the kit goes in the accelerator pump chamber underneath the pump or not??

 

[kenny nunez]

On the Rochester model the aluminum ball is held down in the pump well with a circular wire ring.
Was there a similar one in the pump well of the Marcarb? If not then that ball may have been used on an earlier model. Does the pump plunger on your carburetor have 2 plunger cups back to back? If so then there is a check ball in the plunger body if my memory is correct.
I never cared for the Mercarb, I know it had to be used because Rochester stopped making them. If it was my engine I would have looked for a older Rochester to rebuild.

 

[IanFS]

On the Rochester model the aluminum ball is held down in the pump well with a circular wire ring.
Was there a similar one in the pump well of the Marcarb? If not then that ball may have been used on an earlier model. Does the pump plunger on your carburetor have 2 plunger cups back to back? If so then there is a check ball in the plunger body if my memory is correct.
I never cared for the Mercarb, I know it had to be used because Rochester stopped making them. If it was my engine I would have looked for a older Rochester to rebuild.

Thanks Kenny
Yes I think you are right about the Rochester Inlet Check Ball and although they are similar in most respects, they have differences. Now you mention it I seem to remember, as you say, that Rochester stopped making carbs for Mercruiser.
No mine only has a single plunger and its the 4cc version with a 90 degree connection.
A lot of people have said that the Mercarb is troublesome but I have to say I have not had trouble from it, just this question about the Aluminium Check Ball.
I've since managed to find someone (Mike Carburetors) who can tell me about the Aluminium Ball and it seems that my version doesn't use it, only the Stainless one under the Venturi. The earlier versions with the straight rods have 2 holes in the Accelerator Chamber and this Aluminium Ball is used in those.
The kit I bought only has the 4cc pump but still has the 2 check balls, one Stainless and one Aluminium, how stupid.

 

[IanFS]

Duplicate post. Tried to delete but no delete button!!!

 

[IanFS]

Hi all, I hope you are all well.
I'm rebuilding my Mercarb serial number 3304 9565 model year 7Y 03.
I've been searching through the Mercruiser service manual and made a lot of internet searches including a search through the forum, but I can't find a definitive answer for what the aluminium check ball (provided in the kit) actually does or in fact whether it is necessary.
The Manual and Schematic provided in the kit shows the check ball but one source said it was only their on earlier models as a check to stop the piston bottoming out. Others say its something to do with fuel return to the bowl.
Could someone provide me with a definitive answer please? To check ball or not to check ball, that is the question? And what does it do?
Thank you chaps.
Ian

I've quoted and replied to my original question because I was worried that it was not clear about what I was actually asking. However upon reading it again, it is very clear indeed.
Consequently having found an answer elsewhere, I thought it would be helpful to post it, just in case anyone else in the future has the same question.
Apparently, because some Mercarbs have the older type of Accelerator Pump which has a straight arm, they also have 2 holes in the bottom of the cylinder in which it sits, one is for the outlet to the Venturi's and the other is an "Inlet Hole". With this older type of Mercarb, the Aluminium Check Ball is there to stop fuel going back through the "Inlet Hole" , but it also has a retained clip as well to stop it floating around in the float bowl.
The newer type of Mercarb, has a slot in the side of the pump cylinder, as seen in my photos. This slot is basically the "Inlet" to the pump cylinder, but importantly it only has "one" hole. There is another, but it is blocked off by what looks like a ball bearing glued in place. The working hole is the outlet to the Venturi's. The hole in the Venturi assembly (the outlet hole) has a Stainless Steel ball held in by a spring and a T piece. Therefore the Aluminium check ball in the kit is superfluous.
In fact its a bit daft as most kits supply the new type of Accelerator Pump, but not the older type, but they still supply the Aluminium Check Ball, confusing ......yes!!!
I hope this helps anyone doing a future search.


.

 

[Scott06]

I've quoted and replied to my original question because I was worried that it was not clear about what I was actually asking. However upon reading it again, it is very clear indeed.
Consequently having found an answer elsewhere, I thought it would be helpful to post it, just in case anyone else in the future has the same question.
Apparently, because some Mercarbs have the older type of Accelerator Pump which has a straight arm, they also have 2 holes in the bottom of the cylinder in which it sits, one is for the outlet to the Venturi's and the other is an "Inlet Hole". With this older type of Mercarb, the Aluminium Check Ball is there to stop fuel going back through the "Inlet Hole" , but it also has a retained clip as well to stop it floating around in the float bowl.
The newer type of Mercarb, has a slot in the side of the pump cylinder, as seen in my photos. This slot is basically the "Inlet" to the pump cylinder, but importantly it only has "one" hole. There is another, but it is blocked off by what looks like a ball bearing glued in place. The working hole is the outlet to the Venturi's. The hole in the Venturi assembly (the outlet hole) has a Stainless Steel ball held in by a spring and a T piece. Therefore the Aluminium check ball in the kit is superfluous.
In fact its a bit daft as most kits supply the new type of Accelerator Pump, but not the older type, but they still supply the Aluminium Check Ball, confusing ......yes!!!
I hope this helps anyone doing a future search.


.

yes some use the check ball in the well bottom some dont. Its not uncommon in carb kits to get parts and gaskets that fit several versions of the same carb family.
unfortunately you have to pay attention in great detail to what comes out and hopefully your carb hasnt been messed with in the past…