4.3L engine dies when given gas

[jsw102503]

I recently purchased my first I/O. I picked up a 2004 Caravelle 187 with a 4.3L Mercruiser. It has a mechanical carb. Previous owner had the boat winterized but it was only out twice last year. Boat ran well on a hose. I took it to the lake and it ran great for 30-40 minutes. Then it seemed like it ran out of gas. From then on the boat has not run right. It will start and idle effortlessly. But when you advance the throttle the engine dies within 2-3 seconds. You can re-start the motor right away.

My first guess was that the motor was being starved for fuel. I pulled the fuel and separator. I saw no signs of water. There was a little bit of black grit but I'm assuming that's why I have a fuel there. I also checked the in-line fuel right by the carb and it was in great shape. I loosened the gas cap. I removed the spark arrestor and observed the accelerator pump squirting into the carb. After starting and stalling the engine I immediately pumped the accelerator pump and saw it squirt fuel. If the accelerator pump is still squirting fuel I am assuming that my bowl is full and I have a good fuel pump. Is that a fair assumption.

I am writing because I have several paths and I'm not sure which direction to go. Should I dig into the carb or start looking at the ignition system? Is it conceivable that my idle jets and accel pump are good but the high speed jets (?) are clogged causing it to stall at higher rpms?

Any suggestions? Any help is GREATLY appreciated.

Justin

 

[alldodge]

took it to the lake and it ran great for 30-40 minutes. Then it seemed like it ran out of gas

I would suspect the carb needs a good cleaning. The accelerator pump moves some gas, but the jets will not supply enough fuel to keep it running

Do you have a Merc or TKS carb?
The TKS has a round solenoid (item 1) on top side of the carb
https://www.mercruiserparts.com/bam/subassembly/31490/9021/85

 

[jsw102503]

It is definitely a Merc carb. It has the electric choke and no solenoid.

 

[Scott Danforth]

I recently purchased my first I/O. I picked up a 2004 Caravelle 187 with a 4.3L Mercruiser. It has a mechanical carb. Previous owner had the boat winterized but it was only out twice last year. Boat ran well on a hose. I took it to the lake and it ran great for 30-40 minutes. Then it seemed like it ran out of gas. From then on the boat has not run right. It will start and idle effortlessly. But when you advance the throttle the engine dies within 2-3 seconds. You can re-start the motor right away.

how old is the fuel?

My first guess was that the motor was being starved for fuel. I pulled the fuel and separator. I saw no signs of water. There was a little bit of black grit but I'm assuming that's why I have a fuel there. I also checked the in-line fuel right by the carb and it was in great shape. I loosened the gas cap. I removed the spark arrestor and observed the accelerator pump squirting into the carb. After starting and stalling the engine I immediately pumped the accelerator pump and saw it squirt fuel. If the accelerator pump is still squirting fuel I am assuming that my bowl is full and I have a good fuel pump. Is that a fair assumption.

you did use a new filter, correct? if not, and you attempted to re-use a filter, all the filtered crud on the dirty side of the filter is now on the clean side of the filter

the "little black grit" is crud in your fuel system. As AD pointed out, you will need to start with cleaning your fuel system.

I am writing because I have several paths and I'm not sure which direction to go. Should I dig into the carb or start looking at the ignition system? Is it conceivable that my idle jets and accel pump are good but the high speed jets (?) are clogged causing it to stall at higher rpms?

most probable is the fuel system
most likely plenty of crud in your carb - assume you need a full tear down, clean and rebuild ($35 kit and 3 hours of time)
check the contents of your fuel filter - anything other than fresh, clean fuel, assess the contents of your tank. you may need to clean your tank.

 

[jsw102503]

I can't say how old the gas is. It had 3/4 of a tank when I purchased it. I'm not really sure how to even remove that much gas.

I did use a new fuel filter.

Should I go ahead and rebuild the carb or should I try to hook the boat up to a 5 gallon tank of fresh gas first?

 

[Scott Danforth]

test fuel
rebuild carb
pull inspection hatch and pull sender to inspect inside of tank if fuel is bad. you can use the electric fuel pump on the engine to pump the fuel out if needed.

 

[alldodge]

You pulled the filter and found some grit, if the fuel was clear and not yellowing, I would leave it be until after cleaning the carb. Depending on what you find in the carb will determine if further investigation is needed

 

[jsw102503]

Attached is the fuel (and grit) that was in the fuel /water separator. Not sure if that is yellow?

 

[andrewterri]

Yes that is yellow. Gasoline is clear like water.

 

[scoflaw]

Fresh fuel can have different colors depending on the source. Marinas can dose it up pretty heavy after they receive it.

 

[andrewterri]

Scoflaw, I did not know marinas would add anything to the fuel. Is it a stabilizer they put in?

 

[Scott Danforth]

Attached is the fuel (and grit) that was in the fuel /water separator. Not sure if that is yellow?

That is no longer fuel

 

[jsw102503]

Thanks everyone.

The boat was definitely sitting the winter with 3/4 of a tank of gas. The guy I bought it from ran it twice last year so I'm not sure when that fuel was purchased.

I'll go ahead and order a carb kit. Tomorrow I'll try to run it on a 5 gallon can of fresh gas to see how it runs. Regardless of how that runs I'll try to drain the tank. Not sure what I'll do with 30 gallons of bad gas....

 

[andrewterri]

we just had that debate on another post. never did come up with an answer. think the consensus was a very large bond fire. Lol

 

[alldodge]

ran great for 30-40 minutes

Running off fresh gas would be good. While the gas doesn't look good wonder why it ran good for a while. Pump out some and see what it looks like.

 

[scoflaw]

Scoflaw, I did not know marinas would add anything to the fuel. Is it a stabilizer they put in?

I think they call it valve tech, and it's yellow. This is in Ma. don't know about other locales

 

[jsw102503]

I got a chance to run it on a tank of fresh gas. I put a lot of SeaFoam in the fuel. The boat may have run slightly better but would stall at anything over 1500 rpms. The fuel may not be great but I don't think that is the issue.

I've got a carb kit on the way. The only other thing that I can think of is checking fuel pressure. Where do you check the fuel pressure on these engines? I'm used to putting one on the standard rubber hoses. This engine has threaded connectors on both ends of the braided line. I really don't want to cut that. If I put a gauge on the line from the fuel / water separator to the gas tank would that provide an indication of whether the fuel pump was working? Measure the vacuum on the line...

 

[alldodge]

Need to make a in-line Tee with fuel line of get an adapter like this P/N 91-18078
Goes between carb and pump and should read 3 to 7 psi at all rpms

 

[jsw102503]

That piece makes total sense. I know I could probably put one together but I went ahead and paid the $40. It will be nice to be able to rule out the fuel pump.

 

[jsw102503]

I may not be a mechanic but I'm guessing the attached pic of the contents of the float bowl is not a good thing. Jets and everything looked clear but all of that sediment can't do good things. I'm letting it soak so we'll see later today or tomorrow how it runs. Even if that wasn't my issue it was probably worthwhile to get that stuff out.