How much suction from breather at cam?

[I am Groot]

On the standard Stroms set up does it give a fierce or soft vacuum ? Hold your finger when you place it over the end of the breather pipe or can you just feel a very gentle suction that won't hold.
Just trying to establish how much vacume i should have. reason being i have a weber with a breather kit where by a 9.5 mm pipe takes a high/strong vacuum directly from the crankcase point below the carb then via a prv valve and catch can connects to the cam cover. On tick over its got a fair pull that holds your finger. I am concerned it might be to strong and therefore create a weak mixture as its drawing to much air back below the carb. But if the original has a fair pull on it then its just emulating that so no problem. I dont want to burn a valve.
thanks for any help.
nigel

[Phil S]

if a vacuum take off is below the carb butterfly it is full engine intake vacuum and is for something like the distributed advance or servo.
a crankcase will only need a mild depression so would connect above the butterfly.
Phil

[wilf]

The "prv" valve (I assume you mean PCV?) will control the vacuum actually applied to the crankcase.

[flying farmer]

There might be a lot of suck, but because the crankcase is sealed it won't be pulling much volume of air except at initial start up, unless you have an air leak into the crank case.

I fitted one of Stagwebers breather systems on my TR due to an oil leak on the timing cover I couldn't be bothered to fix.
It was a complete disaster due to the flawed design. Worked fine on light throttle settings, but if the engine was worked hard the entire crankcase ventilation had to be done through that 9mm pipe. It couldn't cope with the volume of gasses required, the crankcase over pressurized and the weep of oil turned into an engine soaking mess.

I redesigned it using a T piece and one way valve so it could dump any pressure over atmospheric through a 15mm diameter pipe. This worked well enough that it stayed on the engine until I pulled the engine out last week. Won't be refitting it to the new engine, I made a much neater design without the catch tank on my K reg stag. If I get a leak problem I will copy that.

Neil

[I am Groot]

There might be a lot of suck, but because the crankcase is sealed it won't be pulling much volume of air except at initial start up, unless you have an air leak into the crank case.

I fitted one of Stagwebers breather systems on my TR due to an oil leak on the timing cover I couldn't be bothered to fix.
It was a complete disaster due to the flawed design. Worked fine on light throttle settings, but if the engine was worked hard the entire crankcase ventilation had to be done through that 9mm pipe. It couldn't cope with the volume of gasses required, the crankcase over pressurized and the weep of oil turned into an engine soaking mess.

I redesigned it using a T piece and one way valve so it could dump any pressure over atmospheric through a 15mm diameter pipe. This worked well enough that it stayed on the engine until I pulled the engine out last week. Won't be refitting it to the new engine, I made a much neater design without the catch tank on my K reg stag. If I get a leak problem I will copy that.

Neil

This is a mk2 active breather i was sent free of charge because the first design wasnt stopping the oil leaks on my timing cover. This one varies from the original, it has a much bigger diameter opening on the base plate giving a lot more suction, then the pcv needs more suction to close off, thirdly it has a second outlet on the catch can allowing a connection to the air filter with a one way valve. Since fitting this the engines been rebuilt and doesnt leak oil but i am thinking its best to run with it still because the engines design is for a breather to remove blow by and surely therefore it can't operate efficiently and give good power output if i run it only with partial breathing above the butterfly?
thanks for your thoughts