Have I got something missing from my Mercarb 2BBL?

[IanFS]

1988 SeaRay Seville 18 4.3L Mercruiser V6 with a Mercarb 2BBL - 7Y03 Manufactured November '87.

I posted a thread asking why my Venturi's might be dripping at around 2/3000rpm.

On this thread NH Guy kindly suggested that on our age of Carb's might have a vacuum issue and that the Power Piston may be faulty. Ive looked into it and my Carb doesn't have a Power Piston....:faint2::facepalm:



Secondly the Assembly Schematic doesn't show it!! :facepalm:



So I'm thinking, is it supposed to be there, or has some bright spark before me decided to remove it?

What do you guys think?

 

[Bt Doctur]

Re: Have I got something missing from my Mercarb 2BBL?

Your venturi`s are pouring out gas at that rpm, your in low cruise . At idle is where you dont want to see dripping

 

[IanFS]

Re: Have I got something missing from my Mercarb 2BBL?

At 1500 no dripping, at 2000 there is occasional dripping ar 3000 it is every 5 seconds.

At idle there is no dripping, is that normal BT Doctor?

 

[Bt Doctur]

Re: Have I got something missing from my Mercarb 2BBL?

see if this helps http://www.boatfix.com/merc/Techbk/94/94hg5b.pdf page 5B-3 #25 is the main jet, fuel from the bowl goes thru the jet, up the venturi, and sprays down into the carb and then into the cylinders.dripping at idle will result in a overly rich condition fouling plugs and poor fuel economy

 

[IanFS]

Re: Have I got something missing from my Mercarb 2BBL?

As I said there is, NO dripping at Idle up to 1500rpm, at 2,000 there is occasional dripping, at 3,000 it is every 5 seconds or so.

Thanks for the info BT Doctor thats very kind, however even on page 5B - 3 it doesn't show the Power Piston but it shows the Power Valve which was in my overhaul kit, I really don't get it, either it should be there or it shouldn't. Interestingly enough though, there is a dotted line coming from the area through a hole in the gasket but it ends with nothing attached between the two different jets. In the Clymer Manual it shows the Power Piston clearly in the Rochester schematic list of parts marked as Number 2 but not in the Mercarb schematic. I'm wondering if it's an error or a modification or design of the Mercarb.

All this leads me to now think that the Power Piston spring should hold down the Power Valve until engine vacuum reaches a certain level then vacuum lifts the piston to release the Power Valve giving more fuel.

Any idea's?

Edit..

http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/mercarb.pdf

Interesting, just found this bulletin... Item no 6 - "Is the Venturi discharging fuel by 2000 rpm?" Answer should be Yes!!!!

 

[achris]

Re: Have I got something missing from my Mercarb 2BBL?

As I said there is, NO dripping at Idle up to 1500rpm, at 2,000 there is occasional dripping, at 3,000 it is every 5 seconds or so.

Thanks for the info BT Doctor thats very kind, however even on page 5B - 3 it doesn't show the Power Piston but it shows the Power Valve which was in my overhaul kit, I really don't get it, either it should be there or it shouldn't. Interestingly enough though, there is a dotted line coming from the area through a hole in the gasket but it ends with nothing attached between the two different jets. In the Clymer Manual it shows the Power Piston clearly in the Rochester schematic list of parts marked as Number 2 but not in the Mercarb schematic. I'm wondering if it's an error or a modification or design of the Mercarb.

All this leads me to now think that the Power Piston spring should hold down the Power Valve until engine vacuum reaches a certain level then vacuum lifts the piston to release the Power Valve giving more fuel.

Any idea's?

Edit..

http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/mercarb.pdf

Interesting, just found this bulletin... Item no 6 - "Is the Venturi discharging fuel by 2000 rpm?" Answer should be Yes!!!!

And there, my friend, is the main source of your problems...

A good friend once likened it to a meal, like this...
Genuine manual = Steak dinner.
Seloc manual = take out hamburger
Clymer = a bag of crushed, stale potato crisps.
(R.I.P. DonS)

Here's a link for you to download the steak dinner, and use that clymer for what it's good for, lighting fires.....

https://docs.google.com/open?id=0B1TAvwZ3TjhfNWFyczBmVUE4Wlk

The Mercarb 2 bbl has a power valve, not a power piston. The piston is in the 4bbl carbs, not the 2 bbl....

Cheers,

Chris......

 

[IanFS]

Re: Have I got something missing from my Mercarb 2BBL?

Arrrr, now maybe I think I wasn't very clear in my first post and assumed incorrectly that you all knew that the schematic is from the Genuine Mercruiser Manual which I use all the time. I only finally decided to look at the book of the dead (clymer) after being frustrated at not finding any good answers from The Mercruiser Manual.
However Chris you are the only fellow to give me the answer. Cheers Old Bean.

 

[stonyloam]

Re: Have I got something missing from my Mercarb 2BBL?

Well here is what mine looks like, you may draw your own conclusions.

 

[81 Checkmate]

Re: Have I got something missing from my Mercarb 2BBL?

Mine is the same as yours.......stonyloam.

2bl Merc carb.

 

[achris]

Re: Have I got something missing from my Mercarb 2BBL?

Yep, that's the actuator for the power valve. Doesn't look very 'pistony' to me....

 

[IanFS]

Re: Have I got something missing from my Mercarb 2BBL?

I think I need to start again in light of the last two posts.

So this from my first post above...............

This is a schematic from the Mercruiser Manual for the Mercarb 2BBL carburettor, mine is a 1987 November. The item, a Power Piston was described to me in a previous thread by an iBoats member. The Mercruiser Genuine Manual doesn't show any form of spring type device (actuator/piston etc etc ) poking down from the Air Horn!!!



This is a picture of my Air Horn upside down, clearly without what was described to me s a Power Piston, indeed now from what Chris has said is an Actuator. However what is even more frustrating it that the Genuine Mercruiser Manual doesn't refer to it by any name, only in some drawings.



Chris, you said that the 4BBL carbs have a piston, but the 2BBL's don't, so what does a piston look like?

Should my Mercarb 2BBL have a thing with a spring on it, whatever you want to call it, bearing in mind I also have a power valve installed? I'm even more confused now. :facepalm:

 

[achris]

Re: Have I got something missing from my Mercarb 2BBL?

Hi Ian,

Yep, you got a bit missing....

Unfortunately that part is not sold separately from the air horn (top of the carb) That's probably why there's no direct reference to it in the manual...... Best you can do is find another carb and rat it out, then set one of them up properly...

 

[IanFS]

Re: Have I got something missing from my Mercarb 2BBL?

Thats great Chris, now at least I know the why and the how. You take care and watch out for those nasty Typhoons down South!! Cheers!

 

[IanFS]

Re: Have I got something missing from my Mercarb 2BBL?

Hi Ian,

Yep, you got a bit missing....

Unfortunately that part is not sold separately from the air horn (top of the carb)

Thats interesting, I've just done some Googling on Mercarb 2BBL Power Piston and Power Valve Actuator in case they have different names and as you say found nothing. however when I Googled Rochester 2GC Power Piston, there are a few of these sold.........heres one!


Power Piston, Rochester 2G 4G - OEM # 7006011, 7009718

I've also read about the transition from Rochester to Mercarb, which was because Rochester went out of business so Mercruiser made a carb based on the Rochester.
Do you therefore think this will fit my Carb?

 

[achris]

Re: Have I got something missing from my Mercarb 2BBL?

Looks good... At $7.50 it's worth a go....