Thanks Denis.Very sound advice.I shall do that once my jumbo economy sack (not) of throttle plate screws gets here.Denis247 wrote: ↑Thu Jan 24, 2019 10:16 pmI'd remove and block all pipes coming from the carbs if I were fault finding this. I've even known a faulty vacuum advance to cause this type of problem, sucking in air, or even cracked pipe between the two. Also any vacuum feed to brake servos or other vacuum devices (my car has vacuum operated heater controls), one way valves or dodgy pipes. Basically, take everything off, and if fault persists check for manifold leaks, it may not be the actual carbs causing the trouble. Just my 2c.
I'll be fitting the solid plates from the HiF44s to isolate those emissions valves.I have managed to form a line of logic that involves them in this episode.The old plates and valves were quite probably gummed right up from several decades of being out of sight and parked up for long periods.I've put a few miles on it this year which must have come as a bit of a shock.I only got the carbs performing nicely for the last 500 miler and then this hanging tickover started,during that trip.So maybe they'd been loosened up enough through a good run to start opening and messing with the mixture.Since fitting the brand new plates with brand new valves (which seem to be slightly longer and open further) the revs have just risen more.
Also,the brake servo operation has been questionable recently, since the fitting of new brake lines and whizzo steel hoses.So the advice about blocking off hoses really started to bite as I typed that.It may be a bit of air in the system or it may be a fault with the genuine antique servo unit.The hose is new.There was a serious vacuum in it last time I whipped it off.
Must admit that rebuilding and tweaking a Holley on my mate's Defender was a delight compared to this.Just had to un-monkey it back to factory settings for it to perform flawlessly.The logic involved there was very uncomplicated.I obviously haven't found all my previous owner's monkeys yet.