Carburetor Issues, Dripping Carbs...

[DangerMouse1]

I recently installed a new carb on a 5.7l mercruiser.

The carb and engine were running fine, and then I had difficulty starting after a few weeks. I looked down the carb and noticed it was dripping and flooding the engine.

I just took the carb apart, cleaned it as I thought maybe the float was sticking, but all looked good.

My only thoughts are that for some reason the float level has changed, or my fuel pump has gone. I have read that sometimes it is the fuel pump, but I don't seem to be having a problem getting gas, and would the needle/float not stop gas even if the pump had too much pressure?

Just wanting to get thoughts on what to do next.

 

[alldodge]

If a speck of crud got in the needle seat, this would cause initial flooding. If needle was not changed the needle "might" have a nick in it from the crud

If fuel pump is at 8 psi or more, the float may not seal it off. Could change the float setting to help compensate or use pressure regulator

 

[DangerMouse1]

Thanks. Ok that makes sense, so if pressure is too high, fuel would get through.

I checked by blowing air through and the float cut the air supply of when it was in the up position, so would this mean it isn't a needle issue?

 

[alldodge]

For the most part yes

 

[DangerMouse1]

For the most part yes

So resetting the float height would probably not achieve much. I'm not sure how I can measure current fuel pump pressure as I currently cant get the engine to start for more than a second?

 

[airshot]

Pull the plugs out and check it by using just the starter

 

[alldodge]

You used air and it cut off the flow. Don't know who much air pressure was used so the comment "for the most part". Changing the float height so the float will close a tad sooner will increase the force if it leaks a bit and the float is pushed harder against seat

If its still flooding, recheck float level and if needed then replace the needle and seat

 

[sdowney717]

So resetting the float height would probably not achieve much. I'm not sure how I can measure current fuel pump pressure as I currently cant get the engine to start for more than a second?

Mechanical pumps limit their fuel pump pressure by the spring that forces the diaphragm closed. Really they dont over pressurize the fuel simply by the way they are made.
Electric pumps that spin may over pressurize the fuel.

 

[DangerMouse1]

Ok. I’m going to try changing pump first then, if that doesn’t work back to carb

 

[alldodge]

You can check fuel pump pressure by making one with a plastic or brass barbed Tee and so rubber fuel line, and carb fitting from auto parts store.

Disconnect from carb, and connect Tee, the use other fitting at carb. Can buy a vacuum fuel pump gauge for $20 or so, or rent from same auto parts store for free

 

[Scott Danforth]

Mercarb or Webber or Rochester?

Electric or mechanical pump?

What is fuel pressure?

If Rochester the welsh plugs could be leaking

If fuel pressure is too high, it will force seat open

 

[DangerMouse1]

The fuel is leaking from the Venturi as well as overflowing sometimes. Looking at cleaning the needle and seat. But just wondering if this Could this be caused by fuel pump pressure being to high? It is a mechanical pump and the carb is a Sierra replacement that I fitted and worked for a few weeks and now doesn’t.

 

[Bt Doctur]

I have a mechanical one in my v6 and it would put out 15 psi when it felt like it and flood the carb. An eaton pump took care of the problem

 

[DangerMouse1]

Yep it is just strange that it just starting happening, and I hate throwing parts at a problem instead of being able to diagnose. @Bt Doctur did you see it coming out of the Venturi? Will see if I can measure pressure, or is it possible to take the pump out of the equation and gravity feed?

 

[Scott Danforth]

Yep it is just strange that it just starting happening, and I hate throwing parts at a problem instead of being able to diagnose. @Bt Doctur did you see it coming out of the Venturi? Will see if I can measure pressure, or is it possible to take the pump out of the equation and gravity feed?

And what is your fuel pressure?

 

[DangerMouse1]

And what is your fuel pressure?

Haven't been able to get fuel pressure yet. Trying to figure out how from the above comments as engine isn't currently running. Sound like I would have to take all plugs out...

 

[Scott Danforth]

Haven't been able to get fuel pressure yet. Trying to figure out how from the above comments as engine isn't currently running. Sound like I would have to take all plugs out...

Your diagnostic measures should be to measure fuel pressure to ensure it's not above 7psi

 

[dubs283]

Still no info on what actual carb this is....

OP: is your carburetor 2 or 4 bbl? What manufacturer created it? Carter or Rochester?......................................

 

[DangerMouse1]

Still no info on what actual carb this is....

OP: is your carburetor 2 or 4 bbl? What manufacturer created it? Carter or Rochester?......................................

it is a 2 barrel, sierra, this one - https://www.summitracing.com/parts/RRA-18-7376N

just looked closely at engine and found it is an electrical pump. had assumed it was mechanical, so sorry for miss-information. Now that I know I should be able to easily test the pressure.

 

[DangerMouse1]

appreciate all the help guys on this one so far.