JamesHigdon Posted November 22, 2011 Report Share Posted November 22, 2011 At 26 years old I was ten years from being born when the last mass market car with points rolled out of the show room…yet they still haunt me. I have a ’68 Chevy with them that gave me fits, an old moped with them that I had to make from lawn mower parts and now a ’71 MGB that makes my head hurt. The car is a trade in I adopted, it was running but ROUGH. I cleaned the carbs and got it running then put about 20 miles on it before it just sputtered and died. I towed it home and a few days later changed the condenser, it was flooded but fired right off after it cleared out then ran rough. I fully rebuilt the twin SU carbs and it fired and ran rough again at which point I went to go check the cap and rotor. The car had off-brand points in it and the post (where the negative wire off the coil and the condenser wire attach) had broken off the base. Here’s where I’m confused…I’m going to break it down. I am getting no spark at the coil or the contacts. I have 12V into the + side of the coil and a wire directly from the – side to the post on the points base stud. The strap from the outboard point contact attached to a part of the stud that has a plastic collar on it to isolate it from the base, then the wire from the condenser and – side of the coil go on the stud. When I tighten down the –coil wire and the condenser wire the nut coming down on the stud grounds the condenser wire, the – side of the coil and the strap from the point contact to the grounded distributor base which doesn’t seem right? What am I missing? It would seem to me the condenser wire, the – coil wire and the contact point strap should be isolated from ground? If I run a jumper from the - side of the coil to the condenser wire and then jumper that to the contact strap then use a screw driver to open the contacts I get a solid blue spark from the coil lead and a solid spark at the contacts. I have tested the condenser by putting a quick 12 volts into it and watching it discharge after so it appears ok, the points are brand new Lucas sport points that came with the car in a box. Right now my best guess is the points are for a positive ground car hence the henky problem? Am I headed in the right direction or doomed? Help Link to comment Share on other sites More sharing options...
4cylfordz Posted November 22, 2011 Report Share Posted November 22, 2011 in points think of it as a series. 12v+ to (+ coil) then (-coil) to points set (tach optional) then point set (the isolated stud) to condenser positive wire then it finally ends at the condenser ground (the case) where you bolt it to the dist base. THERE SHOULD BE NO GROUND ANYWHERE IN BETWEEN THE COIL + AND THE CONDENSER - or it wont ever work. easyiest way to think of it is dont call the - side of the coil negative as it is actually supplying voltage to the points or any other ignition stystem. Link to comment Share on other sites More sharing options...
JamesHigdon Posted November 22, 2011 Author Report Share Posted November 22, 2011 By that idea mines goes coil +, coil -, then gangs power to the points and the condenser off the stud which is grounded to the based plate but has a plastic isolator...I'm beginning to think I have either a bad set of points or points for a 12v + ground system. Link to comment Share on other sites More sharing options...
jwmbishop Posted November 22, 2011 Report Share Posted November 22, 2011 Points are points - regardless of battery ground. They simply break the primary ign circuit to cause the secondary to fire due to the collapse of the magnetic field created when the primary side is closed. That said mgb's (any lucas type including Jags) are finicky as the point set is a bunch of pieces as opposed to the chevy's "cased" set. I fought one for a while and could not remember WHAT I found - but I found this for you - Link. Sounds like you are missing the top insolator? That page is indexed from here with a complete run down of the mgb ign system. Man you think the old stuff hurts YOUR head - you should have tried it without instant support such as the net provides! Link to comment Share on other sites More sharing options...
JamesHigdon Posted November 22, 2011 Author Report Share Posted November 22, 2011 Points are points - regardless of battery ground. They simply break the primary ign circuit to cause the secondary to fire due to the collapse of the magnetic field created when the primary side is closed. That said mgb's (any lucas type including Jags) are finicky as the point set is a bunch of pieces as opposed to the chevy's "cased" set. I fought one for a while and could not remember WHAT I found - but I found this for you - Link. Sounds like you are missing the top insolator? That page is indexed from here with a complete run down of the mgb ign system. Man you think the old stuff hurts YOUR head - you should have tried it without instant support such as the net provides! Ok, I'm impressed; how did you find that website as I've been looking for a good picture of Lucas points online for a few days now. A few of those pictures show exactly what the problem is, my new set of points was missing the top insulator, nut and washer right out of the box. I installed the points and found another nut but didn't know i was even missing a part until now. The good news (or bad maybe) is that I have now been forced to learn more about points then anyone me age should know...12 v + into the coil, an oscillating 12 v + out of the negative post into the stud on the base plate which is ground isolated, branches from the stud to the strip leading to the contacts and the condenser. The condenser absorbs some of the charging from the coil and discharges as the points open causing the coil to spark. Link to comment Share on other sites More sharing options...
jwmbishop Posted November 22, 2011 Report Share Posted November 22, 2011 I googled "71 mgb ignition diagram" - it was the third hit. Link to comment Share on other sites More sharing options...
JamesHigdon Posted November 22, 2011 Author Report Share Posted November 22, 2011 I googled "71 mgb ignition diagram" - it was the third hit. I was more along the lines of "Lucas Points" and the like; either way thanks. I happen to think the older stuff would have been easier when you could walk over to another car nearby and see what the point setup was supposed to look like. I can't even walk into a parts store and buy points anymore much less call or talk to someone that knows what the are supposed to look like. I can run oscilloscope tests on HEI's to find magnetic pickup issues all day long but points...forget about it. Link to comment Share on other sites More sharing options...
jwmbishop Posted November 22, 2011 Report Share Posted November 22, 2011 with good contacts and properly dwelled points run pretty good. My fav setup on my old camaro was a mallory dual point marine - had 4 bumps rather than 8 - instead of both points breaking just about simultaneously - each set ran half the engine. pain to dwell in but when dialed in it was really crisp. But I do like electronic a ton more. just always keep in mind - the juice goes from battery to ign switch to ballast and through the coil and the points are a grounding switch. always make sure they are not grounded when opened - even on lawn mowers and magnetoed motorcycles - they work the same way... a quick way to test is using a light bulb in series at the positive wire to the coil (between wire and lug) points close = light on, points open = light off, in your case this test would have shown the coil negative to be constantly grounded - missing insulator on the points travel arm. I have improvised many times with lawn mowers and Tecumseh industrials! A conversion from hot-spark is available for that old lucas (same distributor in the EU Ford Cortina - so there are many sources)! just about 60.00 bucks - i built a Jag once that simply came unglued with the extra ooomph the tighter timing control of electronics gave - well that and setting up the advance curve. point float can really rob the 4k rpm and up power, spring em to avoid float and the rubbing block gets eaten away... Link to comment Share on other sites More sharing options...
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