Persistent carb leak & in early run 4HP Lightwin (1969 Model 4906B)

[Good Trout To You Sir]

Persistent and dangerous fuel leak through carb throat (and perhaps other carb openings). Motor starts, but throttle must remain advanced 3/4 to WOT to keep running and even then the rpms are very low --- idle speed at best. After remote tank is disconnected and fuel flooding issue abates through combustion or leaks, engine will move from barely idle speed to very high rpms as mixture leans out just before fuel starvation.
Here's what I've done:
1) Replaced original fuel pump with one I had from a 1987 OMC portable. The '87 small square fuel pump is interchangeable with the 1969 4HP design isn't it? Would fuel pump malfunction lead to flooding through the carb throat? 2) Completely disassembled, soaked carb parts (yes -- welch, plug out), soaked in hot water, sprayed out w/ carb cleaner, tested passages and dried with compressed air. I've done this thrice. 3) New carb body gasket and welch plug. Note here that I've repurposed the high speed nozzle boss gasket. It's not in great shape, but I don't yet have a full parts kit. Noticed mating faces of the carb casting surrounding high speed nozzle look a bit rough --- have assumed this was normal forging of the era. 4) Cleaned and tested high speed nozzle --- and noticed that air passes through the seat / threads of high speed nozzle when compressed air is blown through air intake port on front of carb. Nozzle is seated tightly as possible without damaging. Have assumed this is normal manufacturing of the era. 5) Adjusted float to narrow range of movement (float should drop LESS than standard and should rise/shut off fuel supply SOONER than standard). Valve seat & needle look OK to me. Polished interior of seat with brass cleaner and wooden skewer to facilitate seating of needle. Where am I going wrong? Can someone suggest an interim workaround to high speed nozzle boss gasket replacement that would allow me to continue troubleshooting while I wait for a complete carb parts replacement kit?

 

[kbait]

Persistent and dangerous fuel leak through carb throat (and perhaps other carb openings). Motor starts, but throttle must remain advanced 3/4 to WOT to keep running and even then the rpms are very low --- idle speed at best. After remote tank is disconnected and fuel flooding issue abates through combustion or leaks, engine will move from barely idle speed to very high rpms as mixture leans out just before fuel starvation.
Here's what I've done:
1) Replaced original fuel pump with one I had from a 1987 OMC portable. The '87 small square fuel pump is interchangeable with the 1969 4HP design isn't it? Would fuel pump malfunction lead to flooding through the carb throat? 2) Completely disassembled, soaked carb parts (yes -- welch, plug out), soaked in hot water, sprayed out w/ carb cleaner, tested passages and dried with compressed air. I've done this thrice. 3) New carb body gasket and welch plug. Note here that I've repurposed the high speed nozzle boss gasket. It's not in great shape, but I don't yet have a full parts kit. Noticed mating faces of the carb casting surrounding high speed nozzle look a bit rough --- have assumed this was normal forging of the era. 4) Cleaned and tested high speed nozzle --- and noticed that air passes through the seat / threads of high speed nozzle when compressed air is blown through air intake port on front of carb. Nozzle is seated tightly as possible without damaging. Have assumed this is normal manufacturing of the era. 5) Adjusted float to narrow range of movement (float should drop LESS than standard and should rise/shut off fuel supply SOONER than standard). Valve seat & needle look OK to me. Polished interior of seat with brass cleaner and wooden skewer to facilitate seating of needle. Where am I going wrong? Can someone suggest an interim workaround to high speed nozzle boss gasket replacement that would allow me to continue troubleshooting while I wait for a complete carb parts replacement kit?

Carb bowl chamber must vent to atmosphere. If vent is clogged, fuel will pour out carb throat when pumping primer bulb.

 

[Crosbyman]

remove the carb... think of it as a toilet bowl both work the same way to shut off the filling

turn the carb upside down and blow air in the inlet with your mouth....

if air goes in the inlet the needle and seat assembly are not working properly... fix or replace

make certain the float does not snag on the gasket or is the wrong size .
when the blow test works the carb should not flood anymore.

 

[racerone]

Correct-----Sometimes folks will see a leak.------Then plug the hole where the fuel is leaking.------Instead of fixing the cause for the leak.------Post pictures of this carburetor and show the hole for the vent.----How did this motor run for you last year ?

 

[Good Trout To You Sir]

Post pictures of this carburetor and show the hole for the vent.----How did this motor run for you last year ?

Thanks for replies. I have been traveling. My family would have been displeased had I lugged a 4HP outboard with us on vacation. Will post carb pics next week when I have returned to it.
Anyone know if the high speed nozzle threading to carb body seat should be absolutely air tight on this late 60's 4HP or if small amount of air at this connection is within tolerance?
Separately --- if high and low speed needles are just barely screwed into ports, under certain conditions would you expect small drops of fuel to be pushed out of the ports in normal operation or should a sufficient vacuum exist to prevent?
Prior to leaving town I had greatly reduced leak. But it's not eliminated. Also achieved a range of controlled speeds.....so I'm moving in the right direction. In absence of complete carb kit component set, I made the following changes at once:
- Swapped the modern carb bowl float for the original cork float.
- High speed nozzle gasket workaround: Used thicker o-ring with better fit from previous o-ring attempt.
- Loosened gland nuts of high and low speed needles AND backed out needles until they were somewhat at risk of vibrating out of adjustment ports. I believe the o-ring substitute for proper packing was preventing proper air flow through adjustment ports. Loosening gland nuts and needles seemed to help greatly.

 

[racerone]

The packing washers have nothing to do with----" airflow " ---into the motor.-----The packing washers hold the needles tight so they do not vibrate out of adjustment !

 

[Good Trout To You Sir]

OK. With needles just barely screwed into adjustment port threading, if the smallest amount of fuel emits from adjustment ports, does this fundamentally point to a fuel system problem independent of packing size/quality/amount?
Separate Q: Any advice on whether high speed nozzle threading to carb body seat must be absolutely air tight on this model?

 

[Crosbyman]

itpoints to the needles not being screwed in properly you are suppose to gently seat them all the way then unscrew them approx a turn and a half
leaks = poor packing nut must be thight to secure the needle.
this is no different than a garden water hose valve stem ...



see link on carb set up on a JW yours is almost the same in principle

1953-1967 Evinrude Johnson 3HP Tune UP Project Carburetor Tune Up | Outboard Boat Motor Repair

outboard-boat-motor-repair.com

 

[racerone]

Other than jumping all over the carburetor ----What other trouble shooting has been done ?

 

[Good Trout To You Sir]

leaks = poor packing nut must be thight to secure the needle.

New packing has helped -- but gland nut does NOT tighten around SS needle. (Duct tape on SS adjustment knob to hold in place is not a sustainable solution.)
HS needle gland nut DOES tighten properly.
Carb has rubber-type ring/seal at back of HS needle port.
Should same part reside in SS needle port and does this have any relationship to gland nut tightening?
Was encouraged by brief water test........Motor ran very nicely for 15 minutes once I adjusted HS and SS needles. Afterward ran on just one cylinder and less than 50% speed.
Can you suggest part number for an OEM or aftermarket ignition tune-up kit (with coils) that would be compatible?
Thanks!

 

[Crosbyman]

these are your carb parts

Evinrude Carburetor Group Parts for 1969 4hp 4906B Outboard Motor

Online inventory of Evinrude 4906B Carburetor Group parts for 1969 4hp outboard motors. Buy a genuine OEM or aftermarket part.

www.marineengine.com

the nuts are only there to sqeeze the fiber - nylon washers to stop air leaks and fuel leaks while securing the needle shafts
just tighthen down till the shaft are stiff to rotate. adj. the carb and leave alone.

no need for coils if not cracked and they test good 4-8 Kohm secondaries and 1 ohm or less primaries , inspect or replace wires with 7mm metallic cores and replace the boots if your feel they need to be.


but if you have good 5/16 sparks work on the carb issues if not clean up the points if not overly pitted if overly pitted the condensers are likely bad

work on the coil circuit of the non-working plug

it is always best to solve one problem instead of chasing 2 rabbits

 

[Good Trout To You Sir]

the nuts is only there to sqeeze the fiber - nylon washers to stop air leaks and fuel leaks while securing the needle shafts
just tighthen down till the shaft are stiff to rotate. adj. the carb and leave alone.

Thanks, Crosbyman. My follow-up in post below.

 

[Good Trout To You Sir]

SS Gland nut is screwed as far as it will go into the threading and yet the needle is loose. Have used 2 needle packing rings. Must have examined carb parts diagram 25 times....it does not show the rubber ring/seal I'm referencing. The ring/seal is seated inside the carb body (appears to be glued into the body and the packing nuts would be placed against it. It's that ring/seal that is present in the HS needle port but missing from the SS needle port. Is this why the gland nut has no effect in tension on needle?