Petrol drip from Weber's

[adey]

After I stop the engine, I'm getting a petrol drip from my Weber 40's - at the join of the carbs and the inlet manifold. Could that indicate the O-rings have given up the ghost, or is it something more worrying? I've heard that overtightening is a cause of problems, any advice appreciated.

[kenny.]

Have suffered this in the past on carbs, but since I started using the Misab plates instead of the old plastic bodied seals I've never had a leak.......Misab plates are the thin ally plate with a rubber O ring fitted in them. They also should not be locked up tight, you should easily be able to move carbs up and down by hand, and retain a good seal.

 

Kenny HPC

 

 

[I reply to every thread]

Mine 40's did this a few years ago. Fairly worrying as the right hand one was over the distributor on the X-Flow. Tried everything to sort it, Changed the double coil washers to BDA Cotton reel type, rebuilt the carbs, changed the 'O' rings, tore my hair out. I was eventually told it was as a result of my inlet manifold being on a slight incline. When you cut the engine the unburnt fuel sat in the groove and then leaked out. I had everything refaced and that helped a bit - but I never sorted it completely.

That doesn't help much does it? sorry!

Could actually be the 'O' rings!

[I reply to every thread]

PS - I agree with Kenny - Changing to the plates helped as well

[adey]

Thanks all, I didn't know the name for them but it has Misab plates, but I've well overtightened the carbs by the sound of it.

The inlet manifold is on an incline so it sounds that it will always be a bit suseceptible to the problem.

 

As it's a Seven series IV the thought of an engine fire is not a nice idea!

[Roger King]

Carbs should be mounted so that they have some flexibility on the manifold - typically about 12mm up and down movement at the air filters without forcing.

 

Webers are a bit prone to this dripping problem and it cannot always be completely cured. Check the following:-

 

Are needle valves in good condition?

Is float height correct?

Is fuel pressure too high?

 

All of the above can lead to the fuel level in the float chamber being too high. This can then leak out down the main jet.

 

If you are jetted too rich at some point in the rev/throttle position range, you can get puddles of fuel left lying in the carbs after you switch off. This too will drip for a while.

[Westfield]

Adey

 

I suffered the same problem of dripping carbs. I found that by squirting the rubbers between the manifold and carbs with oil that the engine note changed ever so slightly indicating a small air leak. not enough to affect the running but enough to allow the fuel to leak out once the engine was off.

 

what I found was that the alloy plates with the rubber rings bonded to them were not sealing correctly due to a poorly machined manifold. hard to explain, but as the alloy plates with the rubber ring bonded to them were a tight fit on the studs, this prevented the rubber rings engaging fully in the annular grove in the manifold. by drilling the holes in the alloy plates larger, this allowed the rubbers to sit nicely in the groves. result, no more leaks and a slightly better tickover.

 

hope this helps

 

Tony