[abillmann]

Just had the original carb replaced on my '91 1900 ZS. The repair shop--an authorized Mercruiser outfit, so presumably, they know what they're doing--installed a rebuilt carb.

On startup, I get a lot of black exhaust. Sometimes it subsides, but yesterday, when slowly cruising through a channel, the black exhaust was just billowing out. The engine is running pretty rough also. And it definitely lacks power. Obviously, something's amiss.

Is this symptomatic of an overly rich fuel mixture, or does this sound more like a problem with the choke?

I'm sure the shop will check things out and make it right. Still, it's a pain to take it back in, drop it off, fill out the paperwork, etc., if all it needs is a half-turn of a screw somewhere.

[SEMIJim]

Somebody will undoubtedly be along shortly to correct me if I've got this wrong , and you don't mention what kind of carburetor you've got, so my comments will be kind of generic, but...

Originally Posted by abillmann

Just had the original carb replaced on my '91 1900 ZS. The repair shop--an authorized Mercruiser outfit, so presumably, they know what they're doing--installed a rebuilt carb.

Not sure about the assumption, but just because they know what they're doing, doesn't mean they'll always do it right.

Originally Posted by abillmann

On startup, I get a lot of black exhaust. Sometimes it subsides,

Could be idle mixture, except...

Originally Posted by abillmann

but yesterday, when slowly cruising through a channel, the black exhaust was just billowing out.

By "slowly cruising," do you mean above idle?

Originally Posted by abillmann

The engine is running pretty rough also. And it definitely lacks power. Obviously, something's amiss.

Sounds like it.

Originally Posted by abillmann

Is this symptomatic of an overly rich fuel mixture, or does this sound more like a problem with the choke?

Sounds like overly-rich mixture, to me.

Originally Posted by abillmann

I'm sure the shop will check things out and make it right. Still, it's a pain to take it back in, drop it off, fill out the paperwork, etc., if all it needs is a half-turn of a screw somewhere.

Doesn't work that way with most "modern" carbs, to the best of my recollection. True: There is an idle mixture adjustment (or idle mixture adjustments, for some carbs), but everything above that is set by jet size--the changing of which requires carburetor surgery by somebody who knows what they're about.

If the carb's mis-jetted, somebody screwed-up royally in ordering the replacement.

Jim

[abillmann]

While I consider myself somewhat mechanically adept, I've found six words generally apply: "Sir, step away from the carburetor."

I figured it wouldn't be as simple as just messing with a screw or some other easy thing. So SEMIJim is right on the money, as usual!

I took the boat in over my lunch period. Had a heck of a time getting it started and keeping it running. And lots of black exhaust smoke, especially at startup. Luckily, the repair place is only about 200 yards from my slip. And downstream.

The problem was the choke was stuck open. Makes sense, given the symptoms. And since it wasn't properly set and adjusted to begin with, the shop also replaced all six spark plugs as they were undoubtedly fouled up. No charge.

So when I pick it up tonight, hopefully everything is OK. For a while there yesterday, I was about ready to tell passing boaters that for a short period in 1991, Mariah offered a coal-burning engine as part of their upgrade options.

[WetWilly]

Hi abillmann,

"coal-burning engine", that's a good one....

As for your Carb, please keep us updated on the cause and fix. I was wondering who told you the choke was stuck in the open position? I ask because it makes no sense, if it was stuck in the open position, once the motor was up to operating temp, the chock would have opened up anyway and the motor would have run normal, not rich so an open choke will only affect the starting and cold running of the motor until it heats up.

A closed choke on the other hand would have caused all sorts of running issues because the motor's sucking more far more fuel than air, hence one of the symptoms you were describing - black smoke even when the motor was up to operating temperature.

If it was the shop, I would watch them like a hawk, IMHO, I suspect someone isn't being straight with you....

Good luck,
WetWilly

[SEMIJim]

Originally Posted by WetWilly

I was wondering who told you the choke was stuck in the open position? I ask because it makes no sense, ...

Agree with everything WW wrote, except I'm not confident many of these engines would even run at all when up to operating temp and the choke's closed.

Originally Posted by WetWilly

If it was the shop, I would watch them like a hawk, IMHO, I suspect someone isn't being straight with you....

Perhaps it's naive of me, but I like to try to give people the benefit of the doubt. In this case I'd probably write it off as somebody having misspoken themselves.

I'd keep an eye on them for a different reason: They charged you top dollar for a replacement carburetor, then failed to verify proper operation thereafter. Very bad. Especially being as carburetor replacement is child's play for anybody that knows anything about such engines.

Jim

[abillmann]

Willy is correct about the choke being stuck CLOSED, not open. (It was probably me who misspoke or mistyped.)

The head mechanic at the shop said he dealt with it personally when I brought the boat back, and said he wasn't very pleased with the labor quality of the rebuilt carb from Mercury. They removed the choke assembly, readjusted it, changed out a few things, cleaned it, and all is perfectly fine now. They also put six new plugs in.

They turned it around in about three hours. It was an unscheduled appointment, they didn't charge a dime, and were extremely apologetic. I think they definitely had their tail between their legs. I think they're on the up-and-up, though.

Certainly not the cheapest repair, but part of that cost was a new fuel filter, new engine oil/filter, draining bad gas, and 10 gallons of new gas. (Still expensive, though.)