1993 Mercruiser 4.3 2bbl carb running out of power

[Dougbt]

1993 Searay 180 BR sat indoors as usual through summer. Purchased brand new and kept in pristine condition with less than 200 hrs due to lack of use. First time out this summer I noticed some hesitation and very intermittent and random backfiring under load. was able to cruise at slow speeds no problem. Installed fuel conditioner and stabilizer, replaced plugs, cap, rotor, water separator, and carb inlet fuel filter before venturing out again. 2nd time out starts up easily, idles good, once temp reaches normal ventured out again. Everything is good while accelerating under load until I get above 2500 RPM. No back firing heard. At this point it feels like ran out of gas. If I leave the throttle in the same position, the RPM will drop until it stalls. Able to easily start again. If I throttle back to neutral when power cuts out, will drop to idle and keep running and able to reproduce the exact same symptoms over and over. I feel it's a lack of fuel pressure or a possible carb rebuild? Merc serial #0F008471

 

[Scott Danforth]

welcome aboard

agree, 200 hours over 30 years is lack of use. considering there probably was 100 hours put on the first 2 years

rebuild your carb. and you may need to clean your entire fuel system (tank, anti-siphon valve, etc.

the backfiring under load is known as a lean sneeze. that is your motor pre-detonating because the mixture is way too lean

 

[H20Rat]

How long did the engine sit idle? You didn't really specify, but was it not used for a couple years?

I'd give every rubber part in the engine compartment a once-over. Although it seems counterintuitive, lack of use also causes 'wear', but in other ways.

Take for example a accessory drive belt. Might look fine, but it has been in the same position for years. Once you start spinning it, it might instantly develop cracks and split. Same goes for hoses that haven't had heat, pressure, or fluids moving.

Engine gaskets are also suspect. Head gaskets, crank seals, valve cover all can go bad shortly after resurrecting a long sleeping engine.

 

[Dougbt]

welcome aboard

agree, 200 hours over 30 years is lack of use. considering there probably was 100 hours put on the first 2 years

rebuild your carb. and you may need to clean your entire fuel system (tank, anti-siphon valve, etc.

the backfiring under load is known as a lean sneeze. that is your motor pre-detonating because the mixture is way too lean

Thank you for your reply Scott. I'm kind of a over maintenance type. I use the boat 2 or three times a year. touching wood, never had any issues of any kind. kept in heated garage, fuel stabilizer in off season. octane booster with first tank each year. Use fuel treatment regularly.
You mentioned carb rebuild but wondering about the Merc electric low pressure fuel pump. Are they problematic?
Pulled fuel tank sender and took large sample of fuel, all good.
Boat accelerates like new but if I run at a constant 2500 to 3000 RPM for say 10 to 15 seconds all of a sudden RPM drops to nil. If I run below, say 1500 to 2000 RPM no problems at all, can run all day.

 

[Scott Danforth]

Thank you for your reply Scott. I'm kind of a over maintenance type. I use the boat 2 or three times a year. touching wood, never had any issues of any kind. kept in heated garage, fuel stabilizer in off season. octane booster with first tank each year. Use fuel treatment regularly.
You mentioned carb rebuild but wondering about the Merc electric low pressure fuel pump. Are they problematic?
Pulled fuel tank sender and took large sample of fuel, all good.
Boat accelerates like new but if I run at a constant 2500 to 3000 RPM for say 10 to 15 seconds all of a sudden RPM drops to nil. If I run below, say 1500 to 2000 RPM no problems at all, can run all day.

start with a carb rebuild.

test fuel pressure
if fuel pressure is low, look at anti-siphon valve and fuel pickup

anything man-made will fail. everything that does not get maintained is problematic. however for the most part, its not the fuel pump.

 

[Dougbt]

start with a carb rebuild.

test fuel pressure
if fuel pressure is low, look at anti-siphon valve and fuel pickup

anything man-made will fail. everything that does not get maintained is problematic. however for the most part, its not the fuel pump.

fresh disassemble. Carb spotless. Hesitant to soak carb in Pinesol as seen online. Considering spraying with carb clean and blowing everything out with compressed air before reassembling with new parts.
You mentioned the anti-siphon valve. Is that located in the tank.

 

[Nbaas]

air, fuel, spark. In my humble experience the carb is blamed for many issues that aren't the carbs fault. The symptoms do sound like a fuel supply issue. If If the carburetor looks clean, as shown, you can chase common carb issues: float adjustment, tarnish on the jets, carb gasket, and/or vacuum leak. I had a car battery problem where I could idle the vehicle, but as soon as I put it in gear there was a power drop that killed the engine. The dropping rpm until stall and being able to start it again is neat. anti syphon might be it. there is logic there. probably fuel, but check battery?

 

[jonny rotten]

The main jets in the bottom of the bowl are still intact in the pic. Did you remove them?
Float out of adjustment?

 

[Scott Danforth]

fresh disassemble. Carb spotless. Hesitant to soak carb in Pinesol as seen online. Considering spraying with carb clean and blowing everything out with compressed air before reassembling with new parts.
You mentioned the anti-siphon valve. Is that located in the tank.

did you pass a fine wire thru every passage to make sure they are clear? you need to do this.

let me guess, the pinesol thing was on youtube? if so, ignore it. get a container of barrymans carb cleaner (since you can no longer get the good stuff). I have also used acetone or lacquer thinner.

yes, anti-siphon valve is the nipple on the end of the pickup tube in the tank.

 

[Lou C]

pine sol? never heard of that! Yep Berryman's but wear gloves/goggles etc. ESP when blowing out passages! And you need an air compressor, compressed air cans don't cut it. A little hot dog compresser will work.
you can find tools made especially for cleaning out carb passages without damage on Amazon
Some will use ultrasonic cleaners but you need a pretty big one for an automotive style carb.

 

[Dougbt]

did you pass a fine wire thru every passage to make sure they are clear? you need to do this.

let me guess, the pinesol thing was on youtube? if so, ignore it. get a container of barrymans carb cleaner (since you can no longer get the good stuff). I have also used acetone or lacquer thinner.

yes, anti-siphon valve is the nipple on the end of the pickup tube in the tank.

carb rebuilt, anti siphon valve replaced, cap rotor and plugs replaced. going to makeshift some sort of setup to connect a fuel guage to check pressure, if ok then back out to the lake for the test.

 

[Scott Danforth]

they sell a fitting to est fuel pump pressure

 

[nazmen1]

they sell a fitting to est fuel pump pressure

It would be nice to measure the fuel pump pressure and find that as the cause. The fuel pump part number is 861155A3 for my 1998 Bayliner with 4.3L engine has an EBay cost is in the $60 range, Sierra part is 4 times that. Probably the same fuel pump for yours.

With all you have done you might spend half that much trying measure the fuel pressure. I’m not a part swapping guy and would love to find the smoking gun but at this point you have eliminated many of the fuel delivery components buying the fuel pump might be prudent.

Don’t recall if you mentioned the rubber fuel lines from the gas tank to the fuel pump. They are not a big ticket item either.

Please post your findings.

 

[Scott Danforth]

It would be nice to measure the fuel pump pressure and find that as the cause. The fuel pump part number is 861155A3 for my 1998 Bayliner with 4.3L engine has an EBay cost is in the $60 range, Sierra part is 4 times that. Probably the same fuel pump for yours.

With all you have done you might spend half that much trying measure the fuel pressure. I’m not a part swapping guy and would love to find the smoking gun but at this point you have eliminated many of the fuel delivery components buying the fuel pump might be prudent.

Don’t recall if you mentioned the rubber fuel lines from the gas tank to the fuel pump. They are not a big ticket item either.

Please post your findings.

Carter pump (oem) from summit is $49

 

[nazmen1]

Carter pump (oem) from summit is $49

One suggestion to check for fuel line blockage or crimping is to disconnect the fuel lines at both ends ( right at the entry and exit of the fuel pump) and use string trimmer line as a “plumber’s snake” to see if the fuel lines have any obstruction or kinks in them. The string trimmer line is thick enough, flexible enough and clean enough for that purpose. This would go from the fuel pump into the fuel tank and from the fuel pump to the carb inlet.

 

[Dougbt]

One suggestion to check for fuel line blockage or crimping is to disconnect the fuel lines at both ends ( right at the entry and exit of the fuel pump) and use string trimmer line as a “plumber’s snake” to see if the fuel lines have any obstruction or kinks in them. The string trimmer line is thick enough, flexible enough and clean enough for that purpose. This would go from the fuel pump into the fuel tank and from the fuel pump to the carb inlet.

as i mentioned, I did compression test with results of 150 PSI across all cylinders evenly. Replaced spark plugs, rotor, dist cap, anti siphon valve, inline fuel/water separator as it had been a while. Still had issue with lacking power above 2500 RPM. Playing with the throttle and able to reproduce identical symptoms over and over I was convinced it was related to fuel starvation. Since purchasing fittings, a fuel gauge and having to assemble some sort of adapter to connect to fuel system was not that easy, and considering the year of the boat, I decided then to rebuild the merc 2BBL carb. Before taking it out for a run I also considered the age of the boat and purchased a new Sierra low pressure fuel pump. As I said before tend to over maintain my boat. After installing the pump I fired up the boat in the driveway and noticed easier starting, and smoother running. Maybe me just wishing . Finally get out to the lake tomorrow for a test run.

 

[nazmen1]

as i mentioned, I did compression test with results of 150 PSI across all cylinders evenly. Replaced spark plugs, rotor, dist cap, anti siphon valve, inline fuel/water separator as it had been a while. Still had issue with lacking power above 2500 RPM. Playing with the throttle and able to reproduce identical symptoms over and over I was convinced it was related to fuel starvation. Since purchasing fittings, a fuel gauge and having to assemble some sort of adapter to connect to fuel system was not that easy, and considering the year of the boat, I decided then to rebuild the merc 2BBL carb. Before taking it out for a run I also considered the age of the boat and purchased a new Sierra low pressure fuel pump. As I said before tend to over maintain my boat. After installing the pump I fired up the boat in the driveway and noticed easier starting, and smoother running. Maybe me just wishing . Finally get out to the lake tomorrow for a test run.

Two things to check.

1. The flame arrestor on my Bayliner was filled with carbon, dust and debris. Easy to clean with compressed air and wiping with a rag.

2. The electric choke thermostat is connected and operational. Fully opening the choke.

Wishing you success on your next lake run.
Keep us posted.

 

[Dougbt]

Two things to check.

1. The flame arrestor on my Bayliner was filled with carbon, dust and debris. Easy to clean with compressed air and wiping with a rag.

2. The electric choke thermostat is connected and operational. Fully opening the choke.

Wishing you success on your next lake run.
Keep us posted.

Flame arrestor was as clean as a whistle. Choke operation works as it should. My fingers are crossed but I truly believe the fuel pump was an issue. Though I only use the best premium fuel or marine fuel at the dock, I hear horror stories about ethanol now found in fuels and the effects on older carb systems. found this post, food for thought?

Is ethanol gas bad for carbureted engines?
Many of the critical components of a carburetor, such as the main body and float bowls, are die-cast from aluminum or zinc. When these materials are exposed to ethanol or the water often contained within ethanol, it creates a corrosive combination that can lead to carburetor malfunction and potential failure

 

[Lou C]

I think if its 10% E10 you won't have problems, here's the inside of my Quadrajet run on E10 for 15 years....I think it looks pretty good inside! when I did this rebuilt it was 30 years old....

 

[nazmen1]

Flame arrestor was as clean as a whistle. Choke operation works as it should. My fingers are crossed but I truly believe the fuel pump was an issue. Though I only use the best premium fuel or marine fuel at the dock, I hear horror stories about ethanol now found in fuels and the effects on older carb systems. found this post, food for thought?

Is ethanol gas bad for carbureted engines?
Many of the critical components of a carburetor, such as the main body and float bowls, are die-cast from aluminum or zinc. When these materials are exposed to ethanol or the water often contained within ethanol, it creates a corrosive combination that ca

Here is an excellent video about the corrosive effects of ethanol. This author has done many unbiased and honest review of products.

Hoping it’s the fuel pump and that the next photo posted is of your boat wake at 4500 RPM with your smiling face in the foreground.