Sealing Up The Original Weber Airbox

[type26owner]

Haven't tested this installation yet but sometimes it's apparent when it's going to work well and this is one of those times. I'll report back if it does not pass the usage test.

Bought from www.mcmaster some of their neoprene rubber edge trim #8507K15. It's now held on with super glue. It worked surprisingly well even on the rough oil and gasoline soaked inside surface of the fiberglass cover. Did a test glueup piece and found it had to be cut and scrapped back off the fiberglass. The gasoline immersion test while in high temperature usage will be the ultimate determinant though.

WEAR disposable rubber gloves while doing the glueing. I had to replace mine at least six times before I got it glued all the way around and it had dried.

To seal up the far ends of the airbox closed I've got a technique to tightly squeeze the fiberglass to the steel backplate which uses a single bungee cord.

I'm really sensitive to getting this sealed up airtight because a couple of years ago I had a small mystery magnetic something get inhaled into #4 cylinder. It was ugly. Since I had to tear it down anyway that's when I did the modifications and managed to squeeze in the best quality valve stem seals still available, the all teflon ones.
-Keith

[type26owner]

Been driving the car for several weeks now and can report the neoprene seal is still perfectly intact and so is the super glue. No degradation at all from expose to gasoline and heat soaking. Finally can check that item off my list.
-Keith

[type26owner]

It's been six months now and still the seal is in perfect condition.

However, when I got into the cockpit this morning I was exposed to a pungent stench of gasoline vapors. Popped the bonnet open to investigate and found the bungee cord which squeezes the front and rear of the fiberglass airbox lid closed had slipped off on the rear which then allowed the vapors to wander overnight. I don't miss the constant exposure to those fumes at all now.

What does leak out at a rate of several drops per day is a light weight oily substance. It's very annoying to have it ooze from the rear underside of the airbox onto the top of the fiberglass footbox shelf. Best guess is some fuel is trapped in the low pressure standing wave area just upstream of the Weber's air trumpets and there it undergoes some sort of further distillation. The lighter volatile aromatics are sucked back into the induction system but the heavier hydrocarbons fall out into the bottom of the airbox where finally drips out just to annoy me. I've been burning the premium grade of Shell California Reformulated Fuel. Is there another brand of fuel which does not do this?

[mikefromengland]

under neath webber air box in my car use to get soaked all the time to cure this i firstly checked float level which was set far too high.this stopped most of it.next i took out the trumpets sealed these with hylomar .no leaks what so ever.cleaned everything up .i no longer get gased now when i open the bonnet lol.

[type26owner]

Hi Mike,
Did the stuff that leaked out evaporate away if left alone? What type of Webers do you have? Mine are 40DCOE 18 for instance.

[type26owner]

If my theory is correct about the low pressure area then it occured to me there is possibly a way to stop this stuff from dribbling out of the airbox. Just need an object for the vapor to adhere to and then by gravity have it run along a shaft which is tilted down which and directs the ooze back into the throat of the carbie. They can be pieces of wire which just snaps onto the air trumpet. Simple and stupid but I'll bet that'll work great. Since they'd live inside the airbox also unseen.

Having second thoughts and leaning towards soldering a vee shaped wire into the air trumpets with low-temp silver solder. Would be bad to ingest the metal wire accidently.

[mikefromengland]

my carbs are 31 dcoe 40's.the stuff that leaked out diddn't evapourate i had to clean it up .it used to have a little oil in it as well.thats what it lookeed like anyway not just fuel.i also discconected the breather from the air box and blanked off the hole .i then put another pipe on the breather so it dumped any crap on the floor and not in the carbs.i tried just putting a filter on but the fumes of the breather came in the cabin so i did the latter.works fine but be careful whrn you park on someones posh drive as it may leave a mess if you have trashed the car kind regards mike

[lotusanglia1965]

Hi Keith!
Referring to your first post on this subject,where can i get these valve stem seals,how good are they,do you know if they'll still fit with high lift cams? I thought all engines had none fitted originally. cheers,
Martin

[type26owner]

Hey Mike,
Well the fuel here in California does not evaporate at all. I left a cup outside to evaporate away last weekend and found it still there waiting for me today. If the carbie does not efficiently atomize this fuel then you're really screwed cause it'll run like total crap.

I got thinking about the halomar solution and when I took the air trumpets out they were wet with fuel around the outside. Suspect you've indeed found the source of the leaking. Talked to my brother this morning and on his Caterham the 151 Webers leak right onto the top of battery so he's keen to find a solution too. I'm not enthused about using an adhesive like you've done though. My concern is when that joint is broken there is debris generated and those tiny pieces of loose wandering crud are the perfect size to plug up a jet. I'm trying a different approach. Cut out a flat ring gasket of 1/64" thick neoprene rubber sheet to seal up the radial gap around the air trumpets flange and the carb body. Could not push the air trumpet into place with all my might with this gasket in place but the two 10mm nuts and the clamps did so just fine. Once pulled into place and then the clamps are removed it is quite a chore to pull them free again. Looks as though the gasket has a very good chance of being fuel tight. I won't know for a few days if it's done the trick or not. Thanks for the advice.

[type26owner]

The gaskets are easy to make. I just placed the air trumpet on the sheet of rubber and pushed down firmly while running a scalpel around the inside. With some scissors I cut the OD by making it about 5/32" wide just by eye.

The carb body has a counterbored pocket where the air trumpet's flange get inserted. The pocket's edge is sharp and mine had some raised burrs from getting dinged. Removed the burrs and chamfered the edge by about .015" by cutting it with a bearing scraper. This keeps the gasket from getting cut. Man, does it get wedged into there tightly!

This seemed to work so well I'm going to install a set on my brother's Super7 today.

[type26owner]

Oh, this rubber sheet has some type of fabric in it. Have no idea where to buy some or exactly what it is.... just some stuff left over from when my dad was still flying and maintaining his airplane. Good thing because I've got enough to last our needs forever.

Best material to choose for this purpose would be Viton though.

[type26owner]

Had it's first full heat soaking on the way into work today. No fuel is leaking from the rear of the airbox now. Kinda pleasant to open the bonnet and not get a blast of fuel fumes in the face now.

[type26owner]

I can't believe Weber never fitted a similiar type gasket to their carbies. They all leak in this way! Jeez, what a huge difference it makes to not have gasoline fumes permeating from my Lotus anymore.

The radial fit of the gasket must be an interference fit of one or two thou I'm estimating. Even though there are scratches near the bottom where the spring that presses the auxiliary venturi to it's passageway has gouged the carb body from slidding over that area many times it seals there too no problem. If the radial gap is not right for your carbies then perhaps the surface diameter of the air trumpet can be enlarged by building up a coating a few thou thick of a paint. It had better stick really well though. Possibly one could build up that area with the 400F low-temp silver solder and then turn that down on a lathe to the desired diameter. The other option is enlarge the diameter of the counterbore pocket of the carb body to get the right amount of interference fit for your choosen thickness of rubber sheet.

Well worth the effort just for the reduction of anxiety because the fire hazard is greatly reduced. Piece of cake!

[type26owner]

Just had a look at the 151 Webers on the Super7 and they are clearly leaking in the same way. Only problem is the thin rubber gasket is not going to work there. They broached the keyway for clocking the choke and auxiliary venturi much deeper into the carb body past counterbore pocket diameter by another .03". My brother has no other choice but to glue the air trumpets into the carb bodys. Could machine the counterbore pockets larger in diameter but not today. Would solder on a ring onto the OD of the air trumpet flange to size the gap for right amount of interference onto the rubber gasket. Hey, the newer air trumpet is made from one single piece of metal so soldering onto it is not fraught with danger. Mine old style trumpet is two pieces which have been I assume brazed together. Bummer! What a huge mess it's made on the battery.