Why are my Weber carbs so gunky on the outside?

[Jpicardi]

Can anyone help me understand why my Weber carbs get so built up with gunk? See photos. They also get gummy low on the intake manifolds.

[icarp]

it looks like you are missing a stud and a nut on your inner left side carb cylinder number 1 .

Looks like fuel mist from poor sealing gaskets

Ian

[Jpicardi]

Cause for rebuild?
Fire hazard?

[1QuickS]

There are no seals between throttle shafts and throttle housings. When you accelerate, fuel is squirted downward and will impact throttle valves which will migrate onto the throttle shafts. Also, main circuit has fuel flowing through the center of the throttle bore which also lands on the throttle shaft. Additional fuel can be forced from the fuel galleries for the accelerator circuit or from fuel in the float bowls, both can boil due to high engine compartment heat and heat from the heads conducting to the carbs via the intake manifolds after shutdown. Fuel will then wick past the shaft/housing clearance and evaporate on the flanges leaving residue.

[Jpicardi]

Originally Posted by 1QuickS

There are no seals between throttle shafts and throttle housings. When you accelerate, fuel is squirted downward and will impact throttle valves which will migrate onto the throttle shafts. Also, main circuit has fuel flowing through the center of the throttle bore which also lands on the throttle shaft. Additional fuel can be forced from the fuel galleries for the accelerator circuit or from fuel in the float bowls, both can boil due to high engine compartment heat and heat from the heads conducting to the carbs via the intake manifolds after shutdown. Fuel will then wick past the shaft/housing clearance and evaporate on the flanges leaving residue.

Thanks for the reply. Sounds like from your comments this is not uncommon?

[1QuickS]

Common for sure, the more wear between shafts and the plain bearings that support them the more fuel that escapes.

[snbush67]

Originally Posted by 1QuickS

Common for sure, the more wear between shafts and the plain bearings that support them the more fuel that escapes.

Is there a cure? A modification or different bearings?

[1QuickS]

No, but you could install an elastomeric O-ring or X-ring into the ends of the throttle housing since the throttle shafts would keep them in place but the other four journals would not be sealed, machining to receive the seals would be a real trick and then you would need some sort of keeper. Once installed, the O-ring would reduce the length of the journal which would accelerate throttle shaft wear due to increased contact pressure on the parts (shorter length of support and loads are the same so contact pressure over the area of support increases).

There are surface seals known as Forsheda but these have length and that would interfere with both ends of the the shaft coupling and with at least one of the lever arms on the throttle shaft. Plus, these are more like dust seals and not for sealing against fluid loss.

There is the possibility of cutting O-ring grooves into the throttle shafts but that would decrease length of bearing interface as well as dramatically decreasing torsional strength of the shaft. Alternately an O-ring groove could be cut into the housing in the mid-span of each bearing but I am not savvy enough to know how that would be accomplished. Again, bearing length would be decreased.

Another issue with installing fluid containing seals is they will create friction which would result in a difficult to close throttle, not fun to live with.

[Jpicardi]

Originally Posted by 1QuickS

No, but you could install an elastomeric O-ring or X-ring into the ends of the throttle housing since the throttle shafts would keep them in place but the other four journals would not be sealed, machining to receive the seals would be a real trick and then you would need some sort of keeper. Once installed, the O-ring would reduce the length of the journal which would accelerate throttle shaft wear due to increased contact pressure on the parts (shorter length of support and loads are the same so contact pressure over the area of support increases).

There are surface seals known as Forsheda but these have length and that would interfere with both ends of the the shaft coupling and with at least one of the lever arms on the throttle shaft. Plus, these are more like dust seals and not for sealing against fluid loss.

There is the possibility of cutting O-ring grooves into the throttle shafts but that would decrease length of bearing interface as well as dramatically decreasing torsional strength of the shaft. Alternately an O-ring groove could be cut into the housing in the mid-span of each bearing but I am not savvy enough to know how that would be accomplished. Again, bearing length would be decreased.

Another issue with installing fluid containing seals is they will create friction which would result in a difficult to close throttle, not fun to live with.

So, all in all, something I should be able to live with as long as a little sludge build up doesn’t bother me?

[1QuickS]

Exactly. When your carbs need service you will know it by an erratic idle speed and sniffing/sneezing up through the intakes.

Get some spray carb cleaner, spray the gas residue and wipe with a cloth, easy.

[pampadori]

Hope you didn't overlook the one comment about the stud and nut that are missing. You could soon be dealing with drivability issues due to vacuum leaks if you aren't already.

[Jpicardi]

Originally Posted by pampadori

Hope you didn't overlook the one comment about the stud and nut that are missing. You could soon be dealing with drivability issues due to vacuum leaks if you aren't already.

Oh I’m totally overlooking it. Been ignoring it for 6 years. watching it but hasn’t become an issue yet.

[snbush67]

Originally Posted by Jpicardi

Oh I’m totally overlooking it. Been ignoring it for 6 years. watching it but hasn’t become an issue yet.

Beyond a likely vacuum leak, you risk throttle shaft wear and binding. You are probably experiencing both already.

[kent olsen]

Carb cleaner at Napa and spray them off every once in a while. I even use it on oil leaks.