coxy123 Posted April 20, 2019 Author Report Share Posted April 20, 2019 3.5 ohms Link to comment Share on other sites More sharing options...
johny Posted April 20, 2019 Report Share Posted April 20, 2019 ha thats a funny reading! Have you tried the test I described to measure the voltage supply to the coil and end any doubts once and for all about whether your system is modified or not? With that coil resistance I would expect a result of around 9v to earth.... Link to comment Share on other sites More sharing options...
coxy123 Posted April 20, 2019 Author Report Share Posted April 20, 2019 appologies. not good with electrics.it was reading 12v Link to comment Share on other sites More sharing options...
johny Posted April 20, 2019 Report Share Posted April 20, 2019 hmmm ok and what volts show on the other terminal of the coil (-ve) to earth - hopefully zero.... Link to comment Share on other sites More sharing options...
coxy123 Posted April 20, 2019 Author Report Share Posted April 20, 2019 3.5 ohms across coil 0v +ve to -ve 12v +ve to earth 0v -ve to earth Ignition circuit exact same as 1977 US in Haynes. So it has a ballasted wire in loom. Everything seems to be pointing at wrong coil. Link to comment Share on other sites More sharing options...
johny Posted April 20, 2019 Report Share Posted April 20, 2019 I take it the 0v + to - was without the ignition on? However the 12v and 0v on the coil terminals indicates that something is wrong as a ballasted system should normally only supply ~6v. The only time a ballasted system will supply 12v to the coil is when the starter motor is turning the engine over. So the possibilities are: coil open-circuit (but its 3.5ohmn resistance says no), ballast resistor has been removed or bypassed, contacts on starter motor are permanently closed even when not starting which effectively bypasses the ballast. The fact that you have found a non ballast system coil installed indicates to me that someone has fiddled with this before either as a bodge or intentionally..... Link to comment Share on other sites More sharing options...
johny Posted April 20, 2019 Report Share Posted April 20, 2019 If you buy a ballast system coil with a resistance of ~1.5 ohms and supply it with 12v continuously it will produce higher sparkplug voltage which will possibly damage high tension components, burn the points excessively and also itself overheat so that I dont think it will run for very long..... Link to comment Share on other sites More sharing options...
coxy123 Posted April 20, 2019 Author Report Share Posted April 20, 2019 Ignition was on. So as my ballast wire seems to not be working/present, 12v ignition coil is the best option? Link to comment Share on other sites More sharing options...
johny Posted April 20, 2019 Report Share Posted April 20, 2019 hang on with the ignition on you had 12v on coil +ve to earth, 0v coil -ve to earth but 0v coil across the two? That doesnt add up as after the first two readings you should then get 12v across the two terminals.... Link to comment Share on other sites More sharing options...
coxy123 Posted April 20, 2019 Author Report Share Posted April 20, 2019 oh yeah sorry my mistake. 12v + to earth, 12v - to earth, 0v across the terminals Link to comment Share on other sites More sharing options...
johny Posted April 20, 2019 Report Share Posted April 20, 2019 oh that changes everything cos it means your points were open (or a break somewhere) and there wasnt a circuit. Ok well to complete the test you can run a piece of wire from the coil -ve (very important its not the +ve side) to earth to simulate the points being closed and then measure the voltage on coil +ve to earth. Hopefully youll now see ~6v..... Link to comment Share on other sites More sharing options...
coxy123 Posted April 20, 2019 Author Report Share Posted April 20, 2019 it seems to be 8 v 1 Link to comment Share on other sites More sharing options...
johny Posted April 20, 2019 Report Share Posted April 20, 2019 Congratulations that would indicate that you do indeed have the wrong coil! When you get the correct 1.5ohm one installed the same test should give you a voltage reading of about half of the battery voltage ie 6v..... Hope youve understood whats going on and learnt a little bit of electrickery. The ballast resistance is 1.5ohms and the correct coil is 1.5ohms then the voltage to earth at the connection between the two will be exactly half of the 12v supply but if the coil is 3ohms = 2 x 1.5ohms then the voltage reading will be 12/3 x 2 = 8v to earth. 2 Link to comment Share on other sites More sharing options...
Anglefire Posted April 20, 2019 Report Share Posted April 20, 2019 And when cranking you should see the full 12v across the coil (well less than 12 because when cranking the voltage will drop a bit due to the load. ) did you say you tried with a direct feed to the coil when starting? Link to comment Share on other sites More sharing options...
johny Posted April 20, 2019 Report Share Posted April 20, 2019 Yes you could try a direct feed to prove it runs but be careful as the only way to stop the engine if it takes off will be to kill the temporary supply..... Link to comment Share on other sites More sharing options...
coxy123 Posted April 20, 2019 Author Report Share Posted April 20, 2019 Thanks you've been a big help. Will get a new coil asap. Tried a direct feed from battery to coil just does the same thing. Link to comment Share on other sites More sharing options...
johny Posted April 20, 2019 Report Share Posted April 20, 2019 Well I dont suppose it'll be as easy as replacing the coil, wheres the fun in that? However at least thatll be one thing to cross off the list and then you can work methodically through the other possibilities. Let us know how you get on..... Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 21, 2019 Report Share Posted April 21, 2019 With a feed to the coil the points just earth the coil So no spark is no feed No earth A continuous earth ie points incorrectly assembled or short in condenser Duff coil Even a 3 ohm coil on ballasted 6v should give albeit a weak spark Pete Link to comment Share on other sites More sharing options...
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