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Carb rebuild 2bbl MerCarb 1996 43LX

dhyams

Regular Contributor
"I wanted to post "thought

"I wanted to post "thoughts" as I went through my first carb rebuild, mostly for myself as I go...but comments are definitely welcome, especially if you see that I'm doing something wrong
I hope that some of the rambling therein is useful to someone along the way, and I plan to include pictures of things as I go.

2bbl MerCarb, 1996 4.3LX Alpha One V6

July 16:
Weird things:
* all drawings of the carb show three main pieces; mine has only two though. The throttle body is not separable from the main part of the carb.
* my carb drawing shows a retainer clip, filter, and ball underneath the accelerator pump; as far as I can tell, none of that was there in my carb.

Good things:
* one of the main fuel jets was clogged badly; blowing it out with an air compressor after soaking in in SeaFoam cleared the passage.
* test soaked the carb body nuts (that were painted) in Chemtool B-12 (15 minutes), and it didn't look like any damage was done to the painted finish. This makes me feel better about soaking the entire thing; I've already soaked and washed the uppermost part of the carb (the part where the choke plate is attached)
* I haven't yet destroyed any part that is not replaced in the carb rebuild kit

Bad things:
* I can't seem to remove a little T-shaped metal retainer/spring/ball that lives underneath the secondary venturi assembly. I've been working on that for a while.
* Getting all of the gasket material off is quite a chore."
 
"Daniel Hyams
That little &#3


"Daniel Hyams
That little "T" shaped thing holds your accelerator pump check valve mechanism. It should just pry up with a bit of pressure. Lightly stake it in place when re-assembling. No probes,drills or wires in any of the holes, air pressure only.
Bert"
 
Without the check valve the ac

Without the check valve the accel crt. will feed
engine fuel above 1000 rpm via ventury effect on crt. and waste alot of fuel and make it run dog rich. Make sure spring and ball is inserted and that ball seat is spotless clean. I also use B12 with no issues. B12 also helps soften gaskets to aid removal. Be sure to use specs from service manual for float setting and not from kit instructions as they often differ.

Kurt
 
"Just to make sure I understan

"Just to make sure I understand...Kurt, are you talking about the ball/spring that is under the T-shaped thing (under the secondary venturi assembly), or the ball that goes underneath the accelerator pump (which was never there when I disassembled the carb)?"
 
"Yay! I just got the T-shaped

"Yay! I just got the T-shaped retainer+spring+ball out...bent the end of a paper clip just enough so that I could slip it under the T, and pulled up hard with a pair of pliers....

[Yes, I have the carb here at work
crazy.gif
; I couldn't stand it..]"
 
"July 17: Carb Cleaning and Re

"July 17: Carb Cleaning and Reassembly Day

Items of note:
* the two main fuel jets...when I disassembled the carb yesterday, no washers came out, and of course, I didn't notice that fact. When it came time to put those back in, I noticed on the parts diagram that there were supposed to be washers there; and there were replacements in the carb rebuild kit. I stared at those little openings for quite a long time, and also pryed a little in there with a tiny screwdriver, and finally decided that the washers were indeed in there but stuck. So, I didn't put in the new washers from the kit. BUT, I'm not 100% sure that the washers weren't just missing, and now I've repeated the mistake.
* tiny retainer clips are certainly proof that the devil exists.
* Used the spring loaded needle valve assembly, since that was what was there previously. According to the carb rebuild kit directions, this particular carb (806972) does not use the solid-needle variation.

The cleaning and rebuild went pretty smoothly, all in all, although it was very time consuming. I also live in perpetual fear over losing a tiny little part. When I got to the adjustment phase, I found that almost everything in the carb was pretty out of adjustment. I don't know if that's normal over time, or if a previous owner had messed it up, or perhaps I'm messing it up now. Anyway, here goes:

Float: The float drop was set way too low, and the float level was set way too high. I forgot to measure what it was, but it took some significant bending to get the float into spec. I had been warned by folks on marineengine.com that the instruction sheet that comes with the rebuild kit was not correct; however, its number was consistent with my Clymer manual and with the Mercruiser service manual.
Float level: 9/16", Float drop: 1-3/32".

Idle mixture screw: I forgot to note the number of turns here on disassembly, so I backed it out 1-1/4 turns as per my Clymer manual and the Mercruiser manual. The instructions with the rebuild kit says 2 turns. Hmm.
Idle mixture screwn: 1-1/4 turns out.

Accelerator Pump Rod Height; checked this, and it was to spec: 1-5/32"

Choke setting: Admittedly, I had fiddled with this over the last couple of weeks trying to solve my cold start problem. It was set to 2-Rich; as per the Mercruiser service manual, I set it to 2-Lean.
Choke setting: 2-Lean

Choke unloader mechanism: This was at 3mm; I bent a tang on the accel pump lever so that it was 2mm.

Float weight: Hmm, felt like 9 grams? I don't know, I didn't measure it...I just tested it to make sure it wasn't leaking.

Boat testing:
Pulled the boat into the driveway, and pushed the magic button to activate the fuel pump. Nothing...so I pushed again...nothing. A few seconds later, I pushed again, and it ran for about 5 seconds, presumably filling my dry carb bowl. Still not sure why in the world it behaves in this way (need to check the wires at the fuel pump harness maybe....).

Pumped the throttle twice, boat cranked immediately. Now that's a first! The bad news is that it ran for about 15 seconds and died; I'm not sure why. Pumped and cranked again, and she started...of course by this time, our friendly electric choke was wide open, so I helped things along a bit by manually holding the choke almost closed as she warmed up. Then I let her idle for quite a long time, and everything seems fine. The sound of the engine is maybe a little deeper and "throaty" than before...and I *think* idle is little rougher than before. Probably needs an idle mixture adjustment. I want to do that right though, so I put the boat up and called it a day.

Ah, one other thing...I did adjust the idle speed screw; the idle was little too low (she usually idles at 800 rpm), so I bumped it up a little.

I am decently pleased that this carb rebuild was pulled off without any major problems, and also that the boat started so easily. There are still issues, though..I'm not sure why she died that first time (maybe as simple as the choke opening too quickly, before she was warm...that dang electric choke!!), and I especially am not sure why the fuel pump is not activating when I tell it to."
 
"Took boat out this evening, a

"Took boat out this evening, and everything ran and sounded just fine.

Still a little trouble on starting, but not much; it caught and started immediately on turning the key, but then ran for 10 seconds before dying. I cranked again, and she ran find after that.

I still don't understand how to set the idle mixture screw. I tried today on the water, but utterly failed when turning the screw a turn and a half or so didn't affect the RPM. "
 
"Daniel;
Try this for the idl


"Daniel;
Try this for the idle screw:
Fully warmed up, idling in forward at the correct RPM, turn the screw in slowly until it just starts to stumble or run rough. Then back it out about 1/2 turn CCW. This should be good.

If she stalls out when throttling down quickly, back it out another 1/2 turn. If it runs on at all when shut down, screw it in a little.

Rod"
 
"Here are the promised pics, a

"Here are the promised pics, although I'm not sure how useful they will be except for curiosity's sake...

214536.jpg
The two carb halves"">

214537.jpg
More parts"">

214538.jpg
All clean
 
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