Mercarb 2bbl rebuild/service and some questions

[IanFS]

1988 Mercruiser 4.3L Alpha One

Mercarb 2bbl
Serial 3304 9565 made 3rd Nov 1987 (7Y03)

I'm servicing my carb and have bought a new Sierra Service kit. I've taken off the Air Horn...



This is the body


Then I have these items which I put into a bowl as they came out. I've spread them on the paper sheets to show.


I cannot remember seeing an accelerator pump return spring only the spring in the picture which I am sure is the strainer spring.

I now have several questions to ask......
1/ There didn't seem to be an accelerator spring or retainer or strainer in the accelerator pump housing, is it necessary?
2/ There was a check ball which fell out, is it necessary?
3/ The other check ball in the main housing wasn't there and neither was the spring either when I took out the T shaped retainer.
4/ Finally, the spring in the picture which I think is for the Air Horn filter/strainer inlet fule pipe, which way round does it re-assemble?
Is it fitted in first, or after the strainer? There seems to be two differing idea's. The Mercruiser pdf shows it in front of the strainer, in first, but the diagram which came with the kit and Clymer both show it following the strainer, however it doesn't fit inside the strainer...any idea's?

Cheers
English Mariner

 

[IanFS]

Re: Mercarb 2bbl questions

Re: Mercarb 2bbl questions

I think this post may have got lost.

 

[achris]

Re: Mercarb 2bbl questions

Re: Mercarb 2bbl questions

Hi EM, (I think it's Ian... yes?)

Having a look at the Merc service manual I read a few interesting things... (Clymer is not a manual, it's a knee pad, fire-starters or hand wipes, but never a manual...)

I can't see it in the photos. Do you have a 3 hole acc pump lever or a single hole?
For the 3 hole, make sure there is no check ball in the pump well.

1/ You appear to have the later style pump (3302-96551) as in the service manual, which shows a spring below the plunger. Unfortunately I can't find a part number for the return spring. It looks like it's sold with the plunger... Like this -> http://www.mercruiserparts.com/showSpecialPicture.asp?pn=96551

2/ Where did the check ball fall from? (If it was the acc pump well, then read above).

3/ You need to get a check ball and spring in there. They are there to stop a siphoning effect through the accelerator pump into the venturi. I managed to find a part number for you... Nothing listed in any of the V6 carbie breakdowns until 1993! So here it is 3302-809520. Unfortunately, it's expensive... $4.92... Hope that doesn't break the bank (or stop you come visiting next year)...

4/ The strainer for the inlet goes... Spring in to the carb body, then strainer (closed end in first), then a small gasket goes inside the inlet nut (with a big gasket around the outside), then screw the inlet nut on...

Do you have the genuine Merc shop manual? I'm using that and it's really clear and easy to follow....

Chris.........

 

[nola mike]

Re: Mercarb 2bbl questions

Re: Mercarb 2bbl questions

Just rebuilt my carb with a sierra kit--it for sure comes with the check ball, and I think spring as well.

 

[IanFS]

Re: Mercarb 2bbl questions

Re: Mercarb 2bbl questions

Hi EM, (I think it's Ian... yes?)

Yes it's Ian, cheers Chris

Do you have a 3 hole acc pump lever or a single hole?

Single hole...

1/ You appear to have the later style pump (3302-96551) as in the service manual, which shows a spring below the plunger. Unfortunately I can't find a part number for the return spring. It looks like it's sold with the plunger... Like this -> http://www.mercruiserparts.com/showSpecialPicture.asp?pn=96551

Yes its the later larger accelerator pump but over here an assembly is about ?70....ouch!! Rip off or what??

2/ Where did the check ball fall from? (If it was the acc pump well, then read above).

Yes it was from the well.

3/ You need to get a check ball and spring in there. They are there to stop a siphoning effect through the accelerator pump into the venturi. I managed to find a part number for you... Nothing listed in any of the V6 carbie breakdowns until 1993! So here it is 3302-809520. Unfortunately, it's expensive... $4.92... Hope that doesn't break the bank (or stop you come visiting next year)...

I wondered what the ball did, there is nothing in there which is obvious. A friend who is a vehichle technician and has a Japanese vehicle tuning business is looking at it tomorrow morning, so will probably have a spring to fit it somewhere and as nola mike says the check balls are in the kit but no springs.

4/ The strainer for the inlet goes... Spring in to the carb body, then strainer (closed end in first), then a small gasket goes inside the inlet nut (with a big gasket around the outside), then screw the inlet nut on...

Yep, this makes absolute sense, I'm just about to start a bar bee q so I'll use the Clymer as a starter.......

Do you have the genuine Merc shop manual? I'm using that and it's really clear and easy to follow....

I have a pdf which Don sent a link but you know sometimes things can be wrong so I wanted to check with the experts.....

See you soon Chris...and thank you nola mike too.

 

[IanFS]

Re: Mercarb 2bbl questions

Re: Mercarb 2bbl questions

I thought it may be useful to other members to report my findings and update on how my carb service/rebuild went.

Unless you are currently doing a rebuild/service the information may not mean much to you, but if you are you will probably find it very useful.

Firstly the instruction sheets and the Clymer book (the fire lighter....lol) show the inlet strainer spring is inserted after the strainer...the Mercruiser manual on the other hand shows the spring is inserted first, this is correct.

Secondly, when I took the carb apart I found that there was no return spring on the accelerator pump, but there was a check ball in the chamber. This is confusing and so is the Instruction Leaflet. My carb also had a T retainer under the Venturi......but no spring or check ball. This indicated to me that someone had re-assembled the carb incorrectly.....however it had been working all this time until recently, when it had started popping at high revs.

The instruction leaflet shows a check ball under the accelerator spring with a retainer and a strainer too. However my Mercruiser pdf manual does not. In addition the Mercruiser manual does in fact show a check ball with a T retainer under the Venturi, but NOT under the accelerator spring. My mechanic friend (who remaps japanese sports cars to awsome power outputs) and I came to the conclusion that this was the correct specification and rebuilt accordingly. However there was the little problem that there was no accelerator return spring present, which lead us to searching for similar springs on the internet. Spring found we rebuilt the carb having cleaned and blown out all the airways and fuel ways with an airline in his workshop.

The carb went back together easily but the Inlet Needle Spring in the kit was a tad shorter than the original so little adjustment of the float drop was neccessary to achieve the spec of 14mm drop.

The only other issue we found was that someone had nipped up one of the airhorn screws a little too tightly on a previous occassion so a quick measure up revealed it was UNF 10-32 7/8" thread length, 3/16" outside dia. I found one with a 1" thread length which should be long enough to take up the extra thread left inside the casing.

Now for the testing, it's very wet in the UK at the moment and we have got serious flooding in some parts so it may be next week before I can update.

I hope the mods don't mind me writing this as an update.

Always my best
English Mariner