I was driving my bus down the M4 this morning going to Bristol generally at 65 GPS mph and on a couple of occasions on cresting a slight hill, the speed would start to rise and as I took my foot off the pedal it would keep on going for a half a second then suddenly start engine braking with a lurch. It happened not only at WOT but on other occasions when climbing hills not quite flat out..in that case in a lower gear Assuming its probably a sticky advance on the distributor. There are a few occasions on acceleration from low speed it suddenly picks up , not like over rich dying on a cold engine. Am it right?
A) it was. I stripped it down and the advance was sticky. Was a bit of rust/dirt under the advance plate, and a screw holding the vacuum canister on that almost gripped the Accuspark base plate where it went through inside the distributor, locking it ... but that screw was loose . B) I thought this was more likely but it started when I changed the distributor. C) ...the real reason... my size 36 clown shoes get caught under the dash.
Not uncommon for the advance to stick advanced on the repro dizzys, either centrifugal or the vac advance . I nearly alway have to rebuild them before fitting them. One problem is the shaft is too high, causing the rotor arm to rub on the cap. stoping the advance shaft from returning fully. Caused by too thick a nylon spacer and burrs on the metal shims. I replace the nylon spacer with original Bosch fibre spacers (top in the picture) which are a bit thinner and remove any burrs on the shims. The other problem is the vac advance baseplate sticking this one was caused by the spring holding the ball bearing to tightly.
I did loosen off the spring. My starting point was a Bosch from Slough Swapmeet that cost £5 with a bent vacuum canister and actuator arm. It held vacuum and twitched when I tried it out...I started with a 4oz hammer and tapping it back so it looked like it was meant to be there, despite it not being original with holes drilled by the PO to make it fit. I checked it was advancing 28 degrees at high rpm, 8 degrees at 800 rpm Yesterday I straightened the actuator arm from the vacuum capsule a bit more and cleaned up the plate.. And I had originally I had to file out the slot in the central spindle so that a Beru distributor arm would go all the way home. Despite it being a Bosch distributor.. And it goes so much better I had to check the timing although I had taken the distributor out and replaced it by unbolting the clamp from the block, I checked it and it was still spot on.
I did another long run and kept having the issue .. it turned out the secondary barrel on the carburettor was sticking ... it was a bit alarming when you lift your foot to avoid ramming somebody as you come up from behind going flat out up a hill, it keeps accelerating gently. It was down to slight misalignment of some bushes I had fitted and the fact that the Weber carburettor spindles are neither exactly round nor exactly straight. In the end I used some fine valve grinding paste to just grind out the high spots, cleaned it out and tried it again today. Of course some git in a Transit pulled out in front of me and drove slowly up a hill where I wanted to floor it.. But it seems to not stick any more. I think the distributor was sticky too.
A separate issue I know and it had never crossed my mind until I read this thread and looked at this photo, but is it possible for the two wires for the electronic module to interfere with the operation of the vacuum advance, being they are heavy duty compared to points wires? I have one of these (actually a pertronix) fitted to my SVDA. Ever since fitting this distributor (along with an elec module), I have had a flat spot at low revs under load. I have rebuilt the carb and tuned it (a few times now...) but the flat spot pervades. The 009 I had before was fine! I am going to try a different SVDA dissy.
The cables are very flexible silicone insulated cables. You need to check for the correct operation of the centrifugal and vac advance with a strobe light.
Had the bad ball bearing issue with my dizzy, just check that it has full movement when sucking the vacuum tube. The claw on mine was badly worn and the ball dislodged causing shut down. Luckily I wasn't too far from home. Honestly a 123 is the way to go..
I have now fitted a new svda dissy with an electric module. It is the accuspark unit - very cheap, but I have fitted a beru arm and cap just to help. Hesitation and huge flat spot at low revs now gone and after a run and a final tune of the carb to the new dissy resulting in a perfectly running smooth engine So it seems what I thought was a carb tune-up problem was in fact my (svda bosch 205s) dissy playing up, even though there was no play in the shaft and there was decent movement of the vacuum advance under suction. I am keen to refit this bosch unit in due course, and keep the new one as a spare, so does anyone recommend someone who could refurb my original bosch unit (and how much?) or is it easy to do myself (are kits available)? Thanks
I've not personally used them, but I've heard good things about http://www.h-h-ignitionsolutions.co.uk
There's nothing really to change, assuming there's little play in the bushes for the dissy shaft. Just take it to pieces and clean forty years of muck out of it. Will be much better than aftermarket junk.
The main gunge places are the spinning weights under the contact breaker support pkates, the concentric shaft ( to get at the weights pop tiny circlip off under foam pad under rotor arm, carefully pop springs off rotor assembly and lift outer part of rotor shaft) The sliding advance plate has three microscopic bearing pads that drop out under it or it rests on a metal to metal gunged bearing plate. Its all removable amd cleanable. Check the drive dog on the bottom is not too worn. Nothing too difficult with assorted small screwdrivers and a pair of fine needle nosed pliers. Just make sure you keep all the little bits well corralled and take pictures to help put it back. Or you will be elbowing me away from the £10 siezed up distributor at the next swapmeet as a source of parts. Failing taking it apart wash it out with WD-40 and then lubricate the felt pad with 3in1 or similar.
Thanks for that Mike, very helpful. I will make this a project. I am for a while now going to stop tinkering and enjoy the ride for a while
