Mercruiser 3.0 carb rebuild question

R

rm2508j

Cadet
Joined
Jun 7, 2017
Messages
27
Hello everybody. I have a quick question. I am literally sitting at my coffee table right now rebuilding my MerCruiser 3.0 carburetor. The rebuild kit comes with both the solid needle and seat and the spring loaded needle and seat. The question is which option is better solid or spring loaded. I do not know what the carb had in it originally, reason being is I had a automotive carburetor shop overhaul it and they put the wrong needle and seat in it when they did the rebuild. The carburetor part number is 15396A ? 4. I have the overhaul manual for the engine and I printed out numerous overhaul instructions from the Internet but neither explain the options which is better, any thoughts?
 
R

rm2508j

Cadet
Joined
Jun 7, 2017
Messages
27
The original issue was the first start of the day was fine. After the engine warms up to operating temperature and you shut it down fuel would still run out of Venturi for about 3 1/2 minutes until the fuel pressure bled off. The automotive shop that did the overhaul on the card for me last season put the wrong needle and seat in. I take it it was an automotive style, but who knows. I put the solid needle in for now but still have the spring loaded one as a spare. I will see how it goes and change it if necessary. Thank you for the input.. This forum is a godsend for me as this is my first boat.
 
R

rm2508j

Cadet
Joined
Jun 7, 2017
Messages
27
Follow up...... I put the solid needle in, ran the boat up to operating temp. I shut it down and with a stopwatch and flashlight I timed how long fuel drips from the Venturi. It stopped dripping after 1min 45sec. My question is now, is this normal for a Merc cruiser two barrel carburetor? Am I chasing my tail on this? As I said in my previous post this my first boat. I am very mechanically inclined and I don't mind tinkering with this thing, but am I making myself crazy chasing a problem that don't exist? Should I put the spring loaded needle in? Any help on this is greatly appreciated. Thank you in advance for any answers
 
R

rm2508j

Cadet
Joined
Jun 7, 2017
Messages
27
Sorry. I forgot to mention. That this all started because after the engine is up to temp and then shut down, in order to restart I have to go WOT on start up to get her goin again. Maybe this is normal and the problem is me. Lol
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,640
When shut off the carb shouldn't be leaking fuel at all. The float level needs to be adjust to spec on your sheet. It is adjusted by bending the tang as noted in the pic below. Do not bend the float arm

Carb float Adjust.jpg
 
R

rm2508j

Cadet
Joined
Jun 7, 2017
Messages
27
Ok thanks, I will double check the float height, although I set it to spec on reassembly (10 & 27mm) Do you think it would be beneficial to just install the spring loaded needle while I'm in there? I read the merc service bulletin on flooding that you linked to your post and it looks to me that the spring needle is a better option. Would you agree? Thanks for all your help.
 
Scott06

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,784
I had the spring on mine never had that issue. I'd try the spring loaded seat but might want to check fuel pressure is 4-7 psi, if fuel pressure is too high it will over come the needle and seat to still put fuel in the bowl. Also I believe the spring loaded seat uses a different float level than the solid.
 
R

rm2508j

Cadet
Joined
Jun 7, 2017
Messages
27
Thanks guys! I will get back at it and keep you posted on the results. Thanks again!
 
R

rm2508j

Cadet
Joined
Jun 7, 2017
Messages
27
Ok everyone. I put the spring needle in, set the float height according to the Merc O/H instructions (14mm & 27mm). The boat fires up and runs / idles great but still drips fuel from Venturi after shut down. I'm basically at my whits end with this. I'm still having to go WOT to restart after shut down at operating temp. I'm starting to think the fuel pump may be on its way out, would a bad fuel pump increase FP or decrease FP. I just finished rebuilding the engine but reused the original fuel pump. Any thoughts?
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,640
Is this a new needle and seat?
If it is new, then as Scott06 mentioned you need to find out if your pump is putting out to much pressure above 7 psi
 
R

rm2508j

Cadet
Joined
Jun 7, 2017
Messages
27
Yes all new carb guts. I guess I will check fuel press. Next. Would a tired pump actually increase FP?
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,640
rm2508j said:
Yes all new carb guts. I guess I will check fuel press. Next. Would a tired pump actually increase FP?
Click to expand...

No, a tired pump would decrease fuel pressure. It could be the previous owner may have installed the fuel pump with incorrect spacers. If this was done it would increase the pressure
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,640
rm2508j said:
Spacers? This is the first I am hearing of spacers. Can you elaborate? Thanks
Click to expand...

Some, not necessarily yours (no serial number provided) require spacers and additional gaskets when mounting the fuel pump. Without these the pump rod stroke moves to much and can increase the pressure
 
R

rm2508j

Cadet
Joined
Jun 7, 2017
Messages
27
Well gentleman, I put the gauges on it a few min ago and @1k rpm FP was 16psi which is through the roof for a carbureted engine I would think. As soon as I shut it down FP dropped to 4psi. Looking at the pump I see no spacers and I remember when I did the engine rebuild I saw what I thought was just a thick gasket. That is long gone now! So does anyone know how thick of a spacer is needed to get the FP down to normal levels (7psi max). There is nothing in my overhaul manual about it. I will fabricate spacers at work tomorrow, I just don't know how thick. Would .032 or .040 work? Any input is greatly appreciated. I wish I joined this forum a month ago so I wouldn't have wasted so much time going through the carb a half a dozen times. Thanks
 
You must log in or register to reply here.
Top