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Accelerator pump plunger

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Bruce53

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I have two manuals to use when working on my old 1986, 140 HP, 3 L, Stingray: a Clymer Mercruiser Stern Drive Shop Manual 1986-94 and a Seloc Mercruiser Stern Drive 1964-91 Repair Manual. I think the first is great and the second is junk but at least the second did warn me not to put the accelerator pump plunger in the cleaning fluid when I overhauled the unit. The first one did not. I guess the plunger is swollen because it will not come up once it is pushed down even with the springs on it. But, I don't think the plunger was right in the first place. I read somewhere that "newer models", whatever, used a larger pump for more gas. Maybe I have had an oversize plunger in the pump by mistake. The pump didn't work at all in the past and I suspect that it was stuck on part of its travel. The dealler didn't deal with it. The carb part number is 13898490 and the date code is 5301. If anyone can help me on this thing I would be most appreciative....
 
There are two types of carbs....

rochester 2 bbl with TWO air/fuel adjustments screws.

and a japanese look alike with only ONE air/fuel adjustment screw.

Which one do you have?

there are several models of each with different parts. You may have been given parts for the wrong model.

Also are you sure the "umbrella" of the pluunger moves freely in the pocket it resides in before reassembly?
you should be able to move it up and down with two fingers easily.


When rebiulding a carb one of the most important parts to replace is the accelerator plunger!!!
 
No, I needed a pair of pliers to pull it back up once I push it down - obviously something is wrong. I see the Rochester is different from the Mercarb in a few respects and I am thinking that the plunger was oversize when it was last overhauled. I am getting a rebuild kit today and am hoping that the new plunger will be a better fit. The original Mercarb in 1968 had the single idle needle like I have. Kghost, do you mean that the plunger should be able to move inside the pump with only two fingers? Thanks for the help...
 
Yes two fingers,

also there was NO mrecarb in 1968 (rochester only) , maybe 1986.................mercarb has only one air/fuel mixture screw.

again if it was a mercarb and especially the mid 80's, merc did not have its sh!t together yet on repair kits......you had to purchase the parts seperatly.

MAKE SURE you have all needed info and that the carb is the original for the boat motor.

There "should" have been a green/blue metal id plate under one of the bowl screws.......................about the size of a quarter.

Myself when I replace the plunger I tyopically flex the umbrella out and wipe a very small amount of vasoline (very small) in the pump colum and "exersize" the pump umbrella up and down several times before assembly. The outside diamneter must wipe/seal the inside diameter of the colum. (tube/well if you will).

you should hear a clean wipe sound when moving it up/down.
 
All's well here. The new plunger works fine. I did mean 1986. The carb had no tag like the manual showed but the model number was punched into the housing along with a date code. All the parts were packaged very well and it came together easily. May get some salmon after all...
 
All's NOT well now. Starts fine but a bit rough, as it heats up it runs on only two cylinders and smoke. I have checked the valves and the spark timing and the compression and I have swapped plugs and ignition wires around. Cylinders 2 & 3 are always dead. I can disconnect the ignition wires and it still runs the same. Does anyone know a sure way to check the lifters? They are 26 years old and are the only thing that I can think of that would be a problem now. The valves lift fine when the engine is not running so the cams are not burned.
 
The valves lift fine when the engine is not running so the cams are not burned.
Click to expand...
Do you mean all of the rockers move up/down? A broken pushrod will kill a cylinder; rare, but it happens.
 
First you need to clarify dead.

is there no spark or no fire at the two cylinders??

If no spark at the two spark plugs then it is a ignition problem either plugs, wires or cap or even points


if you have spark the you need to determine if the two cyclinders are getting fuel.

if they are getting fuel then look at valves/rockers/pushrods.........do a compression test at this point jusyt to be sure!!
 
Sure do appreciate the suggestions, guys. This is my third boat over the last thirty years so I have seen and fixed a bunch of problems but this one is special...
Many thanks.
 
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