Davewillb Posted March 12, 2011 Share Posted March 12, 2011 Hi, I've been struggling to get my 2.25 petrol to run without backfiring, spitting back through the carb etc. I've swapped the carb for a good spare, set the timing, replaced the condenser, HT leads and points and that's helped a bit but its not drivable still and wants the choke pulled out to run. Today I was pulling the spark plug leads one at a time with the engine running and realised that three of the four cylinders actually run better with the HT lead pulled slightly off the plug so that it arcs to the plug top cap - is this plug problems or the coil possibly? Dave Quote Link to comment Share on other sites More sharing options...
rtbarton Posted March 12, 2011 Share Posted March 12, 2011 Have you set the plug gaps? Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted March 12, 2011 Share Posted March 12, 2011 The only thing that occurs to me is that you are making the system reach a higher voltage before the arc commences, and I don't know why but I wonder if a snappier spark is helping - perhaps there is something that is leaking the charge away with the caps in place that doesn't get a chance when the cap is a little displaced? I will watch this thread with interest since I would love to know the definitive answer Quote Link to comment Share on other sites More sharing options...
Davewillb Posted March 12, 2011 Author Share Posted March 12, 2011 Have you set the plug gaps? Yep they are spot on - I'm going to try swapping the 'good' plug to another cylinder this afternoon, that will be interesting. Dave Quote Link to comment Share on other sites More sharing options...
Davewillb Posted March 12, 2011 Author Share Posted March 12, 2011 Sweapping the plug swapped the problem - looks like I have three duff plugs, I'll believe it though after I've replaced them and the problem is definately gone! Dave Quote Link to comment Share on other sites More sharing options...
Briarston Posted March 12, 2011 Share Posted March 12, 2011 The only thing that occurs to me is that you are making the system reach a higher voltage before the arc commences, and I don't know why but I wonder if a snappier spark is helping - perhaps there is something that is leaking the charge away with the caps in place that doesn't get a chance when the cap is a little displaced? I will watch this thread with interest since I would love to know the definitive answer You are right in what you say. Back in the "old days" a device called a spark intensifier was regularly advertised in various motoring mags. A small tube resembling an in line radio suppressor (when plug leads had real wire in them) was let into the HT. lead. This miracle device contained only a spark gap. Similar results could be obtained by cutting an HT lead and re-connecting via the opposite holes of a button. These tricks were usually done to clear persistantly oily plugs (cheaper than an engine re-build!) A little useless info for you! Quote Link to comment Share on other sites More sharing options...
Diff Posted March 12, 2011 Share Posted March 12, 2011 Check that you have the leads in the right firing order: 1,3,4,2. Regards, Diff. Quote Link to comment Share on other sites More sharing options...
missingsid Posted March 12, 2011 Share Posted March 12, 2011 You are right in what you say. Back in the "old days" a device called a spark intensifier was regularly advertised in various motoring mags. A small tube resembling an in line radio suppressor (when plug leads had real wire in them) was let into the HT. lead. This miracle device contained only a spark gap. Similar results could be obtained by cutting an HT lead and re-connecting via the opposite holes of a button. These tricks were usually done to clear persistantly oily plugs (cheaper than an engine re-build!) A little useless info for you! An old LR Series 1 engine I had, had them built into the plug caps that were fitted but I don't know if it was standard. Marc. Quote Link to comment Share on other sites More sharing options...
simonr Posted March 13, 2011 Share Posted March 13, 2011 My guess would be that the insulation inside the plugs has started to break down. Some of the current that should be in the spark is being lost inside the plug body. By pulling the leads off and introducing an external spark gap, you are reducing the voltage seen by the spark plug - by enough to reduce the internal arcing / loss. Replace the plugs and it will go away! Si Quote Link to comment Share on other sites More sharing options...
cackshifter Posted March 13, 2011 Share Posted March 13, 2011 You are right in what you say. Back in the "old days" a device called a spark intensifier was regularly advertised in various motoring mags. A small tube resembling an in line radio suppressor (when plug leads had real wire in them) was let into the HT. lead. This miracle device contained only a spark gap. Similar results could be obtained by cutting an HT lead and re-connecting via the opposite holes of a button. These tricks were usually done to clear persistantly oily plugs (cheaper than an engine re-build!) A little useless info for you! In the olden days , ie 1970s, you used to able to buy plugs with the gap built in even. Quote Link to comment Share on other sites More sharing options...
Pwyll Posted March 14, 2011 Share Posted March 14, 2011 All this talk about spark intensifiers has got me thinking. My 3.9 has an amplifier module strapped to the side of the distributor. Have I just paid LR £116 for what is effectively fresh air in a little black case? Quote Link to comment Share on other sites More sharing options...
rtbarton Posted March 14, 2011 Share Posted March 14, 2011 All this talk about spark intensifiers has got me thinking. My 3.9 has an amplifier module strapped to the side of the distributor. Have I just paid LR £116 for what is effectively fresh air in a little black case? No - different kettle of fish. You've probably paid LR £116 for something you could have got from Maplin for £11, plus a box. My link Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted March 16, 2011 Share Posted March 16, 2011 No - different kettle of fish. You've probably paid LR £116 for something you could have got from Maplin for £11, plus a box. My link Not the same thing - the Maplin one is intended for points distributors.. Quote Link to comment Share on other sites More sharing options...
rtbarton Posted March 16, 2011 Share Posted March 16, 2011 Not the same thing - the Maplin one is intended for points distributors.. True, wasn't sure whether the V8 one was points or not. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted March 16, 2011 Share Posted March 16, 2011 Or you paid £116 for a ~£30 item readily available from the motor factors: http://www.v8forum.co.uk/forum/viewtopic.php?t=78 Quote Link to comment Share on other sites More sharing options...
need4speed Posted March 16, 2011 Share Posted March 16, 2011 My guess would be that the insulation inside the plugs has started to break down. Some of the current that should be in the spark is being lost inside the plug body. By pulling the leads off and introducing an external spark gap, you are reducing the voltage seen by the spark plug - by enough to reduce the internal arcing / loss. Replace the plugs and it will go away! Si The correct answer to the original post - and it wasnt even recognised.... Quote Link to comment Share on other sites More sharing options...
Pwyll Posted March 17, 2011 Share Posted March 17, 2011 Or you paid £116 for a ~£30 item readily available from the motor factors: http://www.v8forum.c...wtopic.php?t=78 Unfortunately, the quality of factored electronic parts is very patchy. The last amp I bought from a factors lasted ten minutes. As they come with that "open it and we won't take it back" disclaimer coupled with the fact that I was hacked off with the Disco riding around on recovery trucks, I decided to go straight to LR. At least if this one fails within a year I can take it back and they will replace it. Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted March 17, 2011 Share Posted March 17, 2011 Open it and we don't take it back does NOT affect your statutory rights, the product has to be of merchantable quality and last a reasonable period of time. If it is not fit for purpose you are entitled to a replacement. Quote Link to comment Share on other sites More sharing options...
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