Major fuel leak at carburetor

[Christien]

This one came out of nowhere. It's leaking somewhere on the right carb, between 5 & 6. I'm hoping it's just the gasket between the two halves, but it seems to be flowing way too fast for that. Plan is to remove it later tonight or tomorrow and inspect everything, but in the meantime I'd love to hear anyone's thoughts. Here's a video:

http://www.youtube.com/watch?v=uY2GFMQznBc

[rw7810]

yup, it's leaking.. Maybe a stuck float valve ??

[Scott R]

Second the float, it pumps fuel right out the vent like a spigot when it hangs up. First time this happened to me I greatly understood the benefit of PMO putting in the "windows" to view the float level.

[Christien]

Can that be fixed with the carburetor in the car, or is it one of those jobs that's 10 times easier on the workbench?

[1QuickS]

Fuel float needle is below the 18mm hex cap that is just inboard of the fuel supply banjo fitting. It takes a 16mm socket to reach down to it. It may be bad but there is the possibility of a divot that has worn onto the tab of the float that can cause the needle to stick when it is otherwise good. If you get into the needle valve and replace it you will need to reset your fuel height using the external fuel level vial and do so with the engine running. Also, it is good to check fuel pressure at the carb inlets (3.5 psi with the engine running.) If there is a divot then you may want to replace all needle valves and rework the floats to factory geometry and remove the divots while you are at it.

Float is removed by taking top cover off (ten, 8mm hex nuts) and then the fulcrum screw for the float which is safety wired. The slot in these is sometimes rather messed up so be sure to get as large a screwdriver tip inserted as possible and keep the screwdriver aligned so as to minimize the chance for it slipping out.

PMO sight glass would not help you in this situation, if the needle sticks then the bowl will flood.

I send a picture of the divot in the float tab I refer to, you may want to visit my web site Technical page for more info.

[Christien]

Ok, top half off, float isn't stuck, nor is the needle. I put some fuel into the bowl and it promptly drained out, so my bowl is leaking. What could cause that? I'll pull it off and has a look.

[Christien]

Float fulcrum screw is very munched. I'll pick up a wider flathead screwdriver tomorrow, but I'm afraid this one might not be going back in.

[1QuickS]

The divot would only stick the float with everything in place, when the top of the carb is off the issue would not be readily diagnosed. Good that the float is free to "float." When you get it out have a look for a divot, it is a low probability problem but a real one none-the-less. You could also check the needle valve operation while you have everything apart...could be a bit of crud got lodged in the needle seat...do not blow air into the fuel banjo fitting when top cover on the throttle body-you will crush the floats in that throttle body RIGHT NOW! if you do.

Sometimes floats are a little sticky after a rebuild and everything is trying to find its "Happy home" for operation; did you just rebuild your carbs?

[Christien]

Sorry, I should be more clear. The float is floating just fine, and the needle is clean and clear. I pulled the needle out and had a look in the float bowl, then had my wife turn on the fuel pump for a few seconds to fill the bowl. It filled, and the float floated, as it should, but the fuel drained out the bottom of the bowl all over the base of the carburetor and down across the top of the engine. So I wanted to pull the float so I can see where the fuel is draining underneath it. Maybe I should just leave the float in place and pull the whole carb body and look at its underside. I'm worried there's a crack or something.

No, I didn't just rebuild the carbs, and that's the strange thing. I bought them 3 years ago, freshly rebuilt (by a shop, not by me) and put 15k km on them, then rejetted them when I transplanted a 3.0L engine in last summer. I've got maybe 2000km on the transplanted engine, and this leak just developed today. The car came out of winter storage around June 1 (well, earlier but I had a no-start problem that took a few weeks to sort out).

When we first took the car out this morning my wife and I both noticed a very faint fuel smell, but the ground underneath the car was dry, and really, with a 40 year old carbureted car with numerous oil leaks, various odours are quite common, and nothing to be concerned about. I drove it probably 3 or 4 times throughout the day, then late this afternoon stopped at the post office and noticed a puddle underneath, so I drove it straight home. So my thought is that something developed either overnight or first thing this morning, and got worse as the day went on.

[jpnovak]

Are your main jets tight? If loose this would drain the float bowl.

If so, then you should pull the carb and put it on the bench. Use some IPA (rubbing alcohol, not beer ) to trace the leak.

Have you checked the accelerator pump gaskets? these can go dry and leak. The only thing in the bottom of the float bowl that can leak should be the main jet carrier. I hope this is not from corrosion of the bottom of the float bowl.

[1QuickS]

I looked at the video, finally

My initial thought was: the float is sticking after sitting in storage and fuel is filling the bowl and then passing into the auxiliary venturi as its first point of spilling its contents. Then it is landing on the top side of the closed throttle plate and then leaking out the clearance in the journal supporting the throttle shaft. Check for sticking float.

However...if fuel is draining out the bowl after filling and the pump is off (top cover also off so you can view the process) then jpnovak is right; loose main jet holder or other similar issue with its sealing...hopefully no issues with corrosion pinholes or cracks.

[Christien]

Ok, I found the leak. It's coming from the hole circled in the pic. Did a plug screw back itself out? All the schematics of Webers are from the other side, so I couldn't identify what part it is.

[Eagledriver]

I think that's an access hole for when the carbs were made. They use those holes to drill the passages. Just need to plug it somehow. Maybe tap it for a screw and seal with some sealant. The proper fix would be to get the correct plug.

-Andy

[Joe Bob]

I've used hot lead and solder on those....block the back access and flow it in.

[1QuickS]

I make my own cast lead, tapered plugs. If the plug is loose then it can be reseated as a possible fix it. I would remove it and replace with a fresh plug. When I remove them I use a 3/32" bit and drill the plug after making a center using a sharp tool like an ice pick. Then screw a small wood or metal screw (coarse threads) into the hole and pull it out; the plug should come out with it.

Although I haven't tried it I think a piece of fishing weight (split shot) would fit well; use a rounded end punch to set the lead in place.

If you like I will send some plugs to you with a bit more installation info; contact me via my email address which is provided on my web site.

[Mighty2.0]

Paul's on it! I'm looking forward to sending my carbs to him.

[jpnovak]

Agreed, the access hold plug needs to be replaced. Paul will set you straight.

Paul, thank you for your service to this board. You are a fantastic resource.

[1QuickS]

Thanks to all for the kind words.

My passion is to keep the Webers alive and well so we can enjoy our cars!

[KTL]

I had a similar leak on my recent initial fire-up of my rebuild race car engine. Just wanted to echo the comments made about the float/valve sticking issue.

I had the carbs apart to reconfigure them with new jets, venturis, air correctors & E-tubes. Also replaced a float that looked suspect. My problematic leak location was cyl #1 (incidentally the carb with the new float) and after taking the top of the carb off it appeared that a sticky delivery valve was the actual culprit.

I initially replaced the float with a brand new one because I didn't like how the old float appeared to have some interference with the float chamber when the float was high & the chamber would be very full. The new float didn't fix that issue all that much.... Maybe this is another shortcoming of the notorious USA Webers?

I made sure to check the valve actuator tab on the new float before I installed it during the rebuild process. I held the old float next to the new one and looked at the delivery valve tabs. They appeared to be very close in their angle to the float. So I didn't have to adjust the new float tab much at all.

Anyway, my "leak" was a bit puzzling at first. With the pump on, fuel was burbling out of the secondary venturi. So it was obviously a fuel delivery issue because fuel was somehow being pushed into the venturi. I think the reason it was burbling out the secondary venturi because that is the lowest place fuel can be pushed out of my carbs? My carbs have the tall vent tubes installed on the carb tops, so I think that is what would make the fuel seek out the venturi exit point.

So I focused on the float and delivery valve as potential sources of the problem. I put the carb top back on with just a few nuts and fiddled with the float thru the vent tube. Nice tip there by Paul that I gathered from his site. I could insert a hex key in the vent tube and "tickle" the float to see how it was behaving with the top on the carb. All seemed good with how the float moves throughout its range in the chamber.

Since I have a large amount of spare delivery valves in my carb parts collection, I just replaced the valve. Turn on the fuel pump; no leak. Tickle the float with the hex key and I could hear the valve opening and closing by the sound of the fuel surge coming out of the delivery valve.

Put it all back together and all is good; no leak.. Big thanks to Paul as usual for his detailed explanations, both here on the forums and on his website! His information is very detailed and an invaluable resource to us DIY "experts."

That's not where the story ends though......... Like a fool, I assumed only a little bit of fuel may have leaked into the engine cylinder. So I just went ahead and cranked the engine over. Whoops....... engine stops cranking. That's because cyl #1 hydro-locked.

Like I should have done initially, I removed the #1 spark plug, cranked the engine with the starter (with the ignition and fuel pump disconnected) and out spews a considerable amount of fuel. Clean it up, dry out the plug, put it all back together and vroom it fires right up. Lesson learned.

Don't ever underestimate the potential for hydro-lock with a fuel leak at the intake manifold/carbs. It doesn't take much time at all to remove a spark plug and purge the cylinder of any fuel. I got lucky. Had the engine actually fired with the fuel in the cylinder, I could have bent a rod. That's no way to start a freshly rebuilt engine...........