Fuel leaking out of the throttle (butterfly) shaft

[Joshto]

I took down my 3.0's Mercarb to investigate the fuel leak from the throttle shaft, and I'm not sure the shaft play is bad enough. I tested pumping the carb manually (while it had gas in it) and spraying a bit of WD40 on the closed butterfly; anything that drips on the butterfly eventually leaks out through the shaft....is the shaft's exit point missing something outside to prevent gas from leaking? I dont see a brass bushing, but I guess it can still be replaced?

To clarify, the leak happens after turning off the engine or when the boat is off but moving (i.e. being trailered). Fuel drips from the venturis and floods the engine (mainly affects hot starts, 15 min after turning it off). I think I know why it's flooding (the needle seat washer wasn't fully centered). Once I fix the flooding (replace the seat washer with the red fibre washer that came with the kit), all gas should stay in the bowl unless sucked by the engine. So it should not drip anymore. However, if fuel can go out, unmetered air can be suck in through the shaft.

I'm wondering if I'm chasing a ghost with the shaft play. thoughts?

 

[Scott06]

Float bowl is over full and leaking over. Needle and seat , float not working or too much fuel pressure

 

[Joshto]

Float bowl is over full and leaking over. Needle and seat , float not working or too much fuel pressure

Yes I agree. But my question whether the shaft letting fuel out is okay..I'm fixing the flooding, as mentioned

 

[Scott06]

Yes I agree. But my question whether the shaft letting fuel out is okay..I'm fixing the flooding, as mentioned

If you fix the flooding from the bowl you won’t see fuel on the throttle shaft. Shaft isn’t letting fuel out its dribbling down the bore and across the shaft. While after a lot of use the shaft can wear and create a vacuum leak, this is in cars with a lot of miles on them. Can almost be sure the shaft is fine just fix the fuel bowl level issue

 

[nola mike]

I'm actually not sure that this would even be unmetered air. Air is coming in before the venturis so it should draw additional fuel, mixture would still be correct. If anything if would act like the throttle is more open

 

[Joshto]

If you fix the flooding from the bowl you won’t see fuel on the throttle shaft. Shaft isn’t letting fuel out its dribbling down the bore and across the shaft. While after a lot of use the shaft can wear and create a vacuum leak, this is in cars with a lot of miles on them. Can almost be sure the shaft is fine just fix the fuel bowl level issue

I Fixed the seat washer. I'm bench testing the accelerator circuit before out it all back together and I don't understand... why no fuel comes out of the discharge hole when the spring and t are pressing down? I recorded a video but seems to big to attach. See the link

59493

This is "59493" by Joshua on Vimeo, the home for high quality videos and the people who love them.

vimeo.com

 

[Joshto]

If you fix the flooding from the bowl you won’t see fuel on the throttle shaft. Shaft isn’t letting fuel out its dribbling down the bore and across the shaft. While after a lot of use the shaft can wear and create a vacuum leak, this is in cars with a lot of miles on them. Can almost be sure the shaft is fine just fix the fuel bowl level issue

The plunger seems perfect...it fits snugly.

 

[Scott06]

I'm actually not sure that this would even be unmetered air. Air is coming in before the venturis so it should draw additional fuel, mixture would still be correct. If anything if would act like the throttle is more open

it is unmetered, the throttle shaft is below the boosters and the idle and transition circuits. If you are into classic cars some carbs like the Q-jet are real prone to it and very common to have to rebush the throttle plate. The rochester 2 jet like on my 65 gto the throttle plates are cast iron shaft is brass so the shaft gets replaced, revry rearley does it need tobe rebushed.

So even in good shape a little will leak air in but with the idle mix adjustment its normal, only when you get a large amount of air does it start to affect idle quality

 

[Scott06]

I Fixed the seat washer. I'm bench testing the accelerator circuit before out it all back together and I don't understand... why no fuel comes out of the discharge hole when the spring and t are pressing down? I recorded a video but seems to big to attach. See the link

59493

This is "59493" by Joshua on Vimeo, the home for high quality videos and the people who love them.

vimeo.com

check ball missing or stuck . Depends some have check ball in bottom of well that pump goes into. When pump pushes check ball prevents fuel from getting passed back to bowl. There is also a check ball in the discharge line below the staked metal T in there. these can get stuck and not allow fuel to flow. This ball keeps fuel packed in the supply passage to the accel pump nozzle

 

[Scott06]

The plunger seems perfect...it fits snugly.

the accel pump has no affect on the fuel coming out the throttle shaft

 

[nola mike]

it is unmetered, the throttle shaft is below the boosters and the idle and transition circuits. If you are into classic cars some carbs like the Q-jet are real prone to it and very common to have to rebush the throttle plate. The rochester 2 jet like on my 65 gto the throttle plates are cast iron shaft is brass so the shaft gets replaced, revry rearley does it need tobe rebushed.

So even in good shape a little will leak air in but with the idle mix adjustment its normal, only when you get a large amount of air does it start to affect idle quality

You're right, for some reason in my head I was picturing the choke plate/shaft.

 

[Joshto]

the accel pump has no affect on the fuel coming out the throttle shaft

Sorry, I posted from my phone, and it put the comment in the wrong thread. I meant that no gas is coming out of the discharge hole, even though the plunger is in great shape.

 

[Joshto]

check ball missing or stuck . Depends some have check ball in bottom of well that pump goes into. When pump pushes check ball prevents fuel from getting passed back to bowl. There is also a check ball in the discharge line below the staked metal T in there. these can get stuck and not allow fuel to flow. This ball keeps fuel packed in the supply passage to the accel pump nozzle

Yeah, everything is there...steel ball, spring, and T retainer.

Anyway, I spent some time sticking a needle wire (came with a kit) in both directions of the accelerator circuit (from the well and from the discharge hole) and injecting fuel at high pressure with a syringe from both directions. I also slightly expanded the spring around the plunger. After all that, fuel started coming out with the expected pressure. I put the venturi back in (after cleaning it thoroughly) and tested the full acceleration circuit. It's all good now.

I'm going to reinstall the carb in the boat and run it for a while to ensure it is no longer flooding (I put a new needle seat washer, and the float re-adjusted millimetrically again). Hopefully, as you said, once the flooding goes away, the oil leak off the shaft will stop too.

I'll report back once tested.

 

[Scott06]

Yeah, everything is there...steel ball, spring, and T retainer.

Anyway, I spent some time sticking a needle wire (came with a kit) in both directions of the accelerator circuit (from the well and from the discharge hole) and injecting fuel at high pressure with a syringe from both directions. I also slightly expanded the spring around the plunger. After all that, fuel started coming out with the expected pressure. I put the venturi back in (after cleaning it thoroughly) and tested the full acceleration circuit. It's all good now.

I'm going to reinstall the carb in the boat and run it for a while to ensure it is no longer flooding (I put a new needle seat washer, and the float re-adjusted millimetrically again). Hopefully, as you said, once the flooding goes away, the oil leak off the shaft will stop too.

I'll report back once tested.

if you had that much crud in the passages, get a ultrasonic cleaner (cheap off amazon etc is fine) and use it to clean the carb- when i got mine, my carb rebuilding quality improved dramatically

 

[Joshto]

if you had that much crud in the passages, get a ultrasonic cleaner (cheap off amazon etc is fine) and use it to clean the carb- when i got mine, my carb rebuilding quality improved dramatically

I cleaned this carb deeply when I rebuilt it about two months ago. Today, nothing came out- no dirt or anything on the wire....I don't know what changed, honestly. The issues I have been dealing with since rebuilding are the flooding and its consequence: a leak off the shaft. Other than that, the carb works fine... it idles and accelerates fine.