Bluey Circles:
thankyou for that … how does the pump (traditional mechanical pump) know it is on the overrun ? manifold vacuum ?
I tried to find you a video to show its operation but it seems that nobody does one. Basically yes.
City & Guilds or not, you’ve contradicted yourself and dropped a clanger with manifold vacuum. Most big diesels had no flap in the venturi, hence no way to create vacuum when the pedal is lifted. There’s no provision on the rack of the old mechanical pumps to completely cut off the fuel supply unless the engine stop is used, so the cylinders will be receiving the idling fuel.
There can be a pneumatic governor setup using a manifold vacuum but very old technology and to imply this is standard on a mechanical pump is nonsense.
As you say fuel metering can only be controlled between minimum (idle) and maximum values and the fuel can only be cut off by a separate mechanical mechanism physically closing the metering valve, in the governor, as in engine shut off.
He’s not on Bking’s level but Conor has posted his fair share of twaddle whilst trying to make out he’s, a bit like Bking, some authority.
People who know what they’re talking about don’t have to list qualifications or establish credibility as they don’t really care if they make the odd slip up or mistake anyway. If you actually do, or have done a job, you don’t really care if anyone on the internet thinks you did or not.
Yeah that’s true enough, but I didn’t mean to be so blunt, I’m getting old and a bit f*****g miserable sometimes.
Sorry Conor.
Vacuum assisted governing: Thames Trader, early Leyland 600, and I can’t remember whether either the Perkins P6 or R6 were as well.
Regardless of type fuelling is all about matching engine load as instructed at the throttle with engine speed.In which case it’s obvious that zero load in an overrun situation means at most an idle fuel setting unless you want clouds of black smoke and a sump full of unburnt diesel and/or possibly a runaway truck. 
In the case of the old ■■■■■■■ system for example it’s referred to as the high idle setting. 
youtube.com/watch?v=KzuwdxEJfQA
11.31-11.45
cav551:
Vacuum assisted governing: Thames Trader, early Leyland 600, and I can’t remember whether either the Perkins P6 or R6 were as well.
Yes, dead right and another one was the Bedford J2 ? and the fore runner of the trader which was the bonneted 4D. What I said though, was that most big diesels had no venturi flaps, hence no vacuum build up on overrun. Those vacuum governors also had a nasty little habit of splitting / cracking the diaphragm causing a bit of trouble.
The Leyland 6oo’s and 680’s had a habit of no’ 6 injector pipe cracking because they didn’t have enough vibration restraint, so we’d make up a nice new one and put some extra turns in and clamp them up as well. I wish I could remember where we clamped them. 
It’s a simple job to change a 680 power plus injector pipe, but to do it on an 0 600 is an ■■■■■■ of the first magnitude.
cav551:
It’s a simple job to change a 680 power plus injector pipe, but to do it on an 0 600 is an [zb] of the first magnitude.
How’d ya work that out then ? Piece of cake if yer arms are rubber. 