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MG MGB Technical - Vacuum line

Hi All:
Does anyone know what is the purpose of the bubble in the copper vacuum line on 1966 MGBs?
Godspeed in Safety Fast
Jc
John Crawley

I believe it's a flame trap.
Dave O'Neill 2

I think it is a separator to stop fuel getting down onto the vacuum diaphragm, which rots it, although on those carbs the port is above the throat so there isn't much chance of fuel getting in there anyway.

V8s with HIFs don't have one, the port is on the bottom, and its downhill all the way to the distributor from there. I had to replace the capsule twice (at great expense) until I fabricated a separation chamber, been no further problem in the many years since.

A flame trap is usually fitted between carb and crankcase in case a backfire through the carbs ignites fumes in the crankcase. This is on the front tappet chest cover of 4-cylinder engines with PCV, and in each of the rocker cover to carb breather hoses on V8s.
paulh4

I suspect it is a damper to give the line more volume to take any pulses out of the vac supply to the dist. vac. pot---just to make life easier for the pot
V8s don't need one as their vac. supply is a smoother suck
willy
William Revit

Later engines with more or less the same HS carbs didn't have it either, using a plastic tube.
paulh4

Moss call it a vapour trap.

http://www.moss-europe.co.uk/vacuum-pipe-pre-formed-1h919.html
Dave O'Neill 2

For some reason, the original link I posted wouldn't work, so I had to trim it.

The modified link works, but for some reason the 'vapour trap' description changed.

This is the original link, which will need to be copied and pasted.

https://www.moss-europe.co.uk/vacuum-pipe-pre-formed-1h919.html?assoc=136864
Dave O'Neill 2

Thanks for you insights . . .
My '66 GT is very original - I bought it out of 35+ years of storage - original leather seats, red rubber floor mats, carpet etc. It's first owner, a professional lady, never drove it without glove on so lettering on the dash knobs is still bright white. She also kept receipts for every cent ever spent on the car.
The engine didn't fair quite so well as there were a few unknowing or uncaring mechanics who worked on it over the years.
I am attempting a "sympathetic" restoration of the engine compartment. I want to leave it much the way I found it but at the same time repair the bad stuff that's been inflicted on the little car. As an example the engine, including the carbs, had been undercoated with black tar. I can just see some ripoff artist telling the lady, "And for an extra twenty dollars I can undercoat the engine so it doesn't rust." It has taken me 4 months of working nearly every day to clean this crap off.
The "vapor trap" had been cut of and bypassed at some time in its life. After clean the tar off it I found that it was plugged up inside which is probably why it was bypassed.
Again thanks for the comments . . .
Jc


John Crawley

This thread was discussed between 19/01/2018 and 20/01/2018

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