Manifold query

[mojobaby]

While cleaning my manifold today, I decided to clean out the little pipe that connects to the top of the rocker cover(oil breather pipe).
It was absolutely blocked as was the rubber pipe leading to it

When the pipe was cleared I found the reason for the blockage. The hole into the manifold had been closed from the other side (inside the manifold), with welding.

I knocked a small hole through with a hammer and nail and managed to get a 1mm wire through.

I looked at old photos of the carb and noticed that the pipe from the rocker cover is split in 2. one goes to the manifold and the other goes to the top of the carb.


So my question is, are both pipes necessary? And why was the bottom hole welded close

 

[jonigel]

It runs better with the manifold blocked off it is done a lot here ,i have my 1100 engine blocked off , you only need the rocker box to carb one provided it is not too smokey.

 

[mojobaby]

Thanks Jonigel, pity I didn't see your answer a few hours ago.

I drilled a small hole, just 3mm, through the welding that was blocking the hole. If I have any running issues I'll just block the hole again

 

[mr-reno-139]

The reason for the second pipe under the carburettor is to create a suction on the crankcase breather system as a very early form of emission control
If the size of the diameter is too great it effectively creates a weak mixture upsetting running
Most later cars had a small plastic restrictor fitted into this rubber pipe with a 1.6 mm calibrated hole
Leaving this out has drastic effect with a 8mm hole to suck through
Really old 62ish cars had rocker cover rubber pipe going straight down to the ground in common with 50s and 60s cars

 

[mojobaby]

I can understand that, because I once had running issues when the bolts holding the carburettor down worked loose and excess air got sucked in.
As I mentioned to Jonigel, the hole I made was 3mm. If I have to block the hole or reduce the hole size, I'll fit a restrictor in the rubber pipe

 

[angel]

Really old 62ish cars had rocker cover rubber pipe going straight down to the ground in common with 50s and 60s cars

Renault kept this arrangement up to around 1977 on markets with less strict emission rules.

 

[harbourseal]

My configuration is about the same. But with a 32mm solex Seia Carburetor.
The Dutch manual says that the restriction in the hose from the manifold should be 1.3 calibrated mm. Since I didn't get one, I made one myself from a piece of steel bar 8mm in diamater