Carb flooding after rebuild

[Chunks77]

4.3L Mercruiser Thunderbolt V with 2 BBL.

I rebuilt the carb (upper and lower) this week after finding a damaged accelerator pump. Carefully disassembled and reassembled with assistance from my Seloc Manual. This morning, after reinstallation, the engine ran fine for about 15 minutes which included up to approximately 1800 rpm with no issues. Well, the only issue is it was idling high at 1000 rpm. Figured it was an adjustment I could make later in the day but unfortunately the engine quit and I could not restart again.

After examining the carb, I have noticed the venturi is still dripping fuel after the engine is shut off and there is an accumulation of fuel at the bottom of the carb. After waiting about an hour, I went out to try again and she did run for about 45 secs before quitting again with the same results.

I've made the proper adjustments according to the Seloc Manual for the idle speed and idle mixture screws. (unless there's something I'm totally missing here)

Sounds to me like the engine is being flooded with fuel so what additional adjustments can I make? Throttle cable? Is the high idle indicative of a problem such as this?

Thanks.

 

[81 Checkmate]

Did ya set the float level correctly? Could have on your 15 min run jarred crud loose in the fuel line and cloged the new accelerator pump to stay open a bit.

 

[thumpar]

The first thing you need to do is toss out the Seloc manual and use the link from the adults only thread for a factory manual. Then I would check the float.

 

[Chunks77]

Trash the book huh? Can't disagree too much with that. At best, it's been slightly helpful.....

Adjusted the float. It was hanging slightly low. Now set to 27mm. (think I measured from the wrong "toe") However, still the same issue.

No gas should be dripping into the chamber after the ignition is off, correct? There's enough in the bottom of the carb that I can hear a bubbling sound.

Previously have checked the fuel lines and all were clear.

Checked the accelerator pump too. Seems to be free and clear of clogs and moves freely in the chamber.


To be honest, my frustration level is peaked. Just when I fix one problem, another seems to rear it's ugly head.......

 

[thumpar]

Why was the carb rebuilt? Just as a normal thing or was there any problem before?

 

[alldodge]

Trash the book huh? Can't disagree too much with that. At best, it's been slightly helpful.....

Adjusted the float. It was hanging slightly low. Now set to 27mm. (think I measured from the wrong "toe") However, still the same issue.

No gas should be dripping into the chamber after the ignition is off, correct? There's enough in the bottom of the carb that I can hear a bubbling sound.

Previously have checked the fuel lines and all were clear.

Checked the accelerator pump too. Seems to be free and clear of clogs and moves freely in the chamber.


To be honest, my frustration level is peaked. Just when I fix one problem, another seems to rear it's ugly head.......

Correct, no gas should be dribbling.

If you used a new rebuild kit which came with a new needle seat and valve,

If you set the float level correctly,

Then your issues is either your float is sinking and you need a new one, or you have a spick of dirt (something) in the needle seat and valve area.

 

[Chunks77]

15 years old. Damaged accelerator pump when putting the carb back together initially after some troubleshooting. The rubber seat at bottom was torn. Had already bought the rebuild kit since I had it apart.

Previous problem was an inability to throttle up once the engine was running. She'd die after a couple of seconds.

What I can't get over is a good start and run this morning for 15 or more minutes. Turned off, cranked up again just fine, then she died all by herself while at idle. I'm assuming this is do to flooding so I'm looking for advice on what to troubleshoot next.

 

[Chunks77]

AllDodge, thanks for the input. I'll tear the carb apart (again) and check to see if the float sinks. I installed the new needle and seat assembly and all looks normal but I'll get another look at it. Thanks!

 

[alldodge]

15 years old. Damaged accelerator pump when putting the carb back together initially after some troubleshooting. The rubber seat at bottom was torn. Had already bought the rebuild kit since I had it apart.

Previous problem was an inability to throttle up once the engine was running. She'd die after a couple of seconds.

May have been starving for gas and bad accelerator pump

What I can't get over is a good start and run this morning for 15 or more minutes. Turned off, cranked up again just fine, then she died all by herself while at idle. I'm assuming this is do to flooding so I'm looking for advice on what to troubleshoot next.

Agree, my guess is the motor was running fine until the carb flooded it out.

Start by looking to see if it is dripping fuel, if it is you need to either readjust the float or check to see if it is to heavy and is sinking. Is your float a composite or made of brass?

 

[Chunks77]

The float does float in the reservoir. Does this matter?

The old needle seat spring pushes out slightly farther than the new one. I can see an extra lines in the coil. Is it possible the old one is better?

 

[Chunks77]

Well it's not made of brass. Composite plastic of some kind.

 

[alldodge]

The float does float in the reservoir. Does this matter?

The old needle seat spring pushes out slightly farther than the new one. I can see an extra lines in the coil. Is it possible the old one is better?

It takes very little pressure to seal off fuel from coming in the bowl. If properly adjusted there should be no leakage unless there is a speck of dirt or something in the valve. The adjustment is made by bending the tang in the pic below.

 

[thumpar]

It could be that when you rebuilt it you disturbed some dirt or something and that has got into the needle/seat. How did you clean it before putting it back together?

 

[Chunks77]

Cleaned it pretty thoroughly with carb cleaner. But just in case I sprayed again just in case something got in there.

So after noticing the difference in needle seat position with the old versus new spring, I reinstalled the old spring and adjusted the tang (again, but a little higher).

Long story short, she cranked and ran just fine for 30 minutes or so. Idling great at 620 rpm and restarted again after a short break. Maybe the new spring was causing the carb to flood or maybe the tang wasn't adjusted properly (or a little bit of both).

Much appreciate the focused troubleshooting.

See ya on the water.....

 

[thumpar]

Nice. Have fun with it.