I'm working through a number of carb and distributor issues and have arrived at this one
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The vacuum unit has been replaced as it was broken and the vacuum side of things performs as expected, but I seem to have an issue with the mechanical advance. The timing/advance info has been taken from Brick Yards data here: http://www.brick-yard.co.uk/VehicleSpec ... DGdata.htm. Measurements made using a strobe with advance wheel and a couple of different tachometers for the revs.
The van is set to idle when warmed up at 5' BTDC @ 900 rpm, vacuum off. Once the revs are increased the mechanical advance maxs out at about 28' by 2800-3000 rpm (depending on which tachometer I use). This is too early - it should be about 28' at 4200' rpm.
So I've stripped down the distributor to examine the weights and springs. It appears to only have one spring and although there is provision for a second spring, it does look like it might be designed for one: only one arm is weighted and there is no little plastic locating lug on the second un-sprung arm. There is no sign of a broken spring, though there were some small bits of plastic that could have been part of a 2nd spring locating lug. Its all lubricated, nothing dry or seized.
Picture here: https://www.flickr.com/photos/30324212@N04/14303573681/
I have searched the forum and web and I can't find any pictures or info to say if there should be a second spring or not. The nearest I have found is this forum posting http://forum.club8090.co.uk/viewtopic.p ... g#p7980993 which makes me think that a single spring might be correct?
Can anyone help with either confirming there should be only one spring in there? If so mine must be tired/stretched so I need to find one of the correct spec, who might sell one?
(I experimented with adding a second, weaker spring into the vacant position and tested it - it maxed out at 3500 which is a small improvement, though not sure what it does to the shape of the advance curve, but I'd rather have the correct parts in there than randomly adding bits)
Thanks for any help.