Leaky Webers

[BDA]

My Webers are leaking fuel! It appears to be dripping slowly from the soft mount between carb and the manifold. It doesn't seem to happen when the motor is running - I've looked but I haven't caught it then - but it seems only after taking a drive but it may have more to do with engine being hotter.

I've checked the float level (from the emulsion tube position as well as measuring from the float (not on the seam but off the seam, I have brass floats) to the top cover with gasket). One one carb, I made sure the needle and seat weren't getting stuck by taking the needle and seat out and blowing air through it. There didn't appear to be any fuel in the float and it weighed within a quarter of a gram of the weight stamped on it. The emulsion tubes, main jets, air correction jets have all been cleaned recently.

I have been pretty careful tightening my thackery washers and cushions (thackery on the bottom, cushions on the top). I even used a feeler gauge to gauge the tightness of the thackerys.

Any ideas?

[LotusJoe]

Check fuel pressure.

[BDA]

I've been using a low pressure Facet cube pump and I've never noticed this before (which is not to say that it hasn't happened or hasn't been happening before). I'll check the fuel pressure. It will take a bit to rigging.

Thanks, Joe. I'll report back what I find.

[europatek]

Yes I do.  My deduction is wear in the accelerator pump piston. Solved by adding a hole in the plate that sits between the throats (you'll notice the gasket already has  the hole as do newer versions of the carbs).  I had the same problem on a set of carbs on my Elan.   Adding the hole fixed the leak.  Never happened again.

[BDA]

I have to say that I thought briefly that the leak might have been coming from that plate but I discounted that because I didn't see why the fuel would come from there even though it wasn't really making sense that fuel would seep through the soft mounts. But the drips are off the mounting ears of the carb and I figured it must be coming through the soft mounts.

I think you nailed it, europatek! My carbs are no more than 20,000 miles old (but about forty years old). I don't understand why drilling a hole in that plate will solve the problem, but I saw where the newer carbs have it so that will be my next project.

Maybe even amazing! I wouldn't think that the size of the hole is all that significant but a clue would be appreciated.

Thanks!

[europatek]

I made the hole the same as in the gasket, about 10mm I think.

I've had several pairs of Webers on several twincams and pushrods and never had this problem so when it happened on a freshly rekitted pair of carbs I was
bemused.  It appears the fuel is coming from the soft mounts (as it runs down that way) and after several on/off's with the carbs I was scratching my head and searching the interweb for solutions.  I can't remember if I found some hints to the hole or just looked at the gasket and wandered but proceeded and put the hole in.  Presto, no more leaking!

I think the pressure differential from atmo to the other side of the piston draws the fuel down into the chamber behind the plate and thus the leak happens.  The hole allows the pressure the balance and the fuel to not be drawn down.

Hope it works for you.

[BDA]

I think you may be right about pressure differential. I'm very hopeful. Tomorrow, I break out the drill press. I'll report my results.

Many thanks, europatek!

[Certified Lotus]

These are my completely rebuilt Weber carbs by Mike Pierce at Pierce manifolds in Gilroy CA. Mike supplies his rebuilds with the hole in the plate. By the way, every set of Weber’s I have ever sent Mike come back plug and play with only the idle needing adjustment. He knows what he is doing.

[BDA]

A funny thing: a few years ago, I had my carbs off and noticed one of them was missing that plates so I bought a new one from r.d. It didn't have a have a hole. When europatek said the new carbs had holes in that plate, I checked pictures of new DCOEs and they had those holes!

I can believe that Pierce would set your carbs up right. Dave Bean tuned mine on a dyno so I'm pretty confident about the jetting too.

I tell you, I've learned so much about so many things owning, developing, and working on my Europa!