haggis Posted May 7, 2018 Report Share Posted May 7, 2018 Hi all, trying to sort a misfire out on my Gt6 mk1. Initially I thought it was the coil, had a good read of the posts on here, and thought I’d covered everything. So open to suggestions really. it happens when hot, on a day like today, car starts to lose power, eventually coughing, spluttering and finally backfiring when under load. Let it cool down all fine again for a bit. I’ve looked at the ballast situation, looked at my wiring and no obvious signs of ballast resistor or wire, straight forward white/red from starter to fuse board, white to coil from ignoition. No pink flecks or white and yellow wires so have assumed not ballast. Changed to a good quality coil of 4.5ohm, same imp as rubbish inter motor one that was on there ( on local tuners advice, it’s the only one he had! ) changed back to points and condenser, to check the module, still got the problem? I’ve assumed it’s not fuel as I’ve had this problem before and you don’t get all the backfiring ‘popping’ stuff with the power drop. The engine has only covered a few thousand miles since rebuild, but the only thing I didn’t touch was the distributor. It does appear to have a slightly wobbly base plate, I was considering replacing with an complete electronic unit from the club shop if the module was found faulty, but I don’t think that’s the problem as the points proved. Was planning to take it to SEM next weekend, but not looking to hopeful at the moment. ☹️ As always any help appreciated. Thanks hag Link to comment Share on other sites More sharing options...
Anglefire Posted May 7, 2018 Report Share Posted May 7, 2018 I would t rule out fuel. Hot day sounds like it might be evaporating? Carbs getting hot? though it could also be ignition. Check the points gap? Link to comment Share on other sites More sharing options...
dave.vitesse Posted May 7, 2018 Report Share Posted May 7, 2018 You should have a Delco dissy on the Mk1 GT6. However, if you have a Lucas dissy then change the roto arm for the red type. This is because the black repro Lucas roto arms are known to arc to ground and cause miss-fire problems. Dave Link to comment Share on other sites More sharing options...
haggis Posted May 7, 2018 Author Report Share Posted May 7, 2018 Hi Dave & anglefire, thanks for the responses , carbs and fuel lines are heat shrouded/protected so don’t think I’m having issues there, carbs are just warm when up to temperature. The heat shield in the pic is really effective. The engine is HC prefix from a later vitesse and came with Lucas dizzy. Red rotor arm, magnetronic ignition, cap and leads all replaced 2 years ago, only done 2k mikes since. I was considering moving the coil away from the engine and mounting somewhere on the bulkhead, as it’s just so hot. Any thoughts? Thanks hag Link to comment Share on other sites More sharing options...
Russell1972 Posted May 7, 2018 Report Share Posted May 7, 2018 If it's any help that last 2 misfire issues I've had, with TR6 and a GT6 have both been down to rotor arm and distributor cap. Both showed the symptoms you describe, fine when cold but splutters and misses when hot. In both cases I spent time suspecting fuel and the coil. Having said that, I have also moved the coil from the engine to the bulkhead on the GT6. Russell. Link to comment Share on other sites More sharing options...
haggis Posted May 7, 2018 Author Report Share Posted May 7, 2018 Hi Russell, thanks for that, I will order a rotor and cap as I don’t have spares anyhow, thinking that moving the coil to the bulkhead is a good idea. Hag Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 8, 2018 Report Share Posted May 8, 2018 You havnt got spark plugs with an R in the suffix ??? I found these cause chaos with out low HT coils And if balasted ignition feed a 1.5 ohm coil Unbalasted a 3 ohm coil Run a 1.5 on 12v andd they fry eggs blow rota's and overload Pete Link to comment Share on other sites More sharing options...
rlubikey Posted May 8, 2018 Report Share Posted May 8, 2018 Is this happening at speed and it clears when you slow down? Only tends to happen on hot, dry days? Check the valve gaps. Maybe one or more are a bit small and are closing up when hot. Been there, got that tee shirt! Cheers, Richard Link to comment Share on other sites More sharing options...
haggis Posted May 8, 2018 Author Report Share Posted May 8, 2018 Hi Pete/Richard, firstly definately no R on the spark plugs 'S' suffix in fact, and yes Ive assumed no ballast, can't find any signs of it can't see anything on the wiring diagram to suggest Mk1's had any. Does it matter if the coil is above 3.0ohms? I have one in the garage that reads 68 ohms?? the one on the car is 4.5ohms, was considering buying the lumenition correct one for the magnetronic module, but not sure if it will make much difference.??? I had considered doing the tappets, a little bit noisy on start up. I'll give it a go see how I get on. Thanks again Hag Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 8, 2018 Report Share Posted May 8, 2018 Syou realy need to check if you have a 12v ign or a ballasted 6v A meter on the coil feed with points open should tell you If you have a 6v supply on a 4.5ohm coil you will have a right weedy spark and not good at 12v either 3 ohms for 12v and 1.5 for 6v heck knows where a 4.5 came from Most electronic units dont like a 6v power supply Needs a 12v feed to the dizzy trigger Pete Link to comment Share on other sites More sharing options...
jamesdennison Posted May 8, 2018 Report Share Posted May 8, 2018 My magnetronic ignition burned out a couple of coils before I bought the recommended magnetronic coil. Can't vouch for whether this will sort your problem, but 15 years later the magnetronic coil is still working, so they are a quality item. Link to comment Share on other sites More sharing options...
NonMember Posted May 8, 2018 Report Share Posted May 8, 2018 42 minutes ago, Pete Lewis said: Syou realy need to check if you have a 12v ign or a ballasted 6v A meter on the coil feed with points open should tell you I think you mean "with points closed". The ballast is just a resistor; if the points are open there is no load and the coil feed will show 12V regardless. Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 9, 2018 Report Share Posted May 9, 2018 Thats correct,, senior typo Needs the load , not freshnair Pete Link to comment Share on other sites More sharing options...
haggis Posted May 9, 2018 Author Report Share Posted May 9, 2018 Hi all, ok, so how do you measure voltage when you have a magnetronic module fitted ? I rang the club shop today about the lumenition MS3 coil and they said it was 1.5ohm, assuming I have no ballast then this must be wrong. I’m confused now! Hag Link to comment Share on other sites More sharing options...
haggis Posted May 9, 2018 Author Report Share Posted May 9, 2018 On another point anyone got experience of the new distributors from the club shop? I’m tempted buy the pre installed electric ones but wanted to stick to lumenition apparently the manufacturer use their own version. Thanks again hag Link to comment Share on other sites More sharing options...
Cookie Posted May 9, 2018 Report Share Posted May 9, 2018 It could be fuel vaporisation particularly if you have an electric fan fitted. If you do have an electric fan then throw it away and fit the standard mechanical fan, that cured a lot of overheating, pinking and misfiring issues on my GT6 in hot weather, particularly in slow traffic or after a traffic jam. The issue is that an electric fan blocks off a large area of the radiator due to the motor in the centre, GT6 radiators are small enough without making it worse! Link to comment Share on other sites More sharing options...
haggis Posted May 10, 2018 Author Report Share Posted May 10, 2018 Hi cookie, I think I’ve reduced the chances of fuel evaporation with the heat shielding of carbs and fuel line around the engine. It has a Vw golf rad and revotec fan and temperature seems to hold well in all conditions. The plan is to put an aluminium one on in the future and then hopefully put an original fan back on, but for now it seems to be ok with this set up and it means I can keep on driving it. Thanks hag Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 10, 2018 Report Share Posted May 10, 2018 The coil feed is built in the harness if ballasted will be a dull white wirenwith a dul pink trace If its got an external ceramic resistor its on the baulkhead near the coil If its a full 12v feed then its just a white wire If its ballast has been bypassed it could be anything With electronic I would check the voltage in the dizzy line with the engine being turned you should see the meter change as the unit triggers The are only electric switches to replace the mechanical ones , no fancy stuff inside Pete Link to comment Share on other sites More sharing options...
dougbgt6 Posted May 10, 2018 Report Share Posted May 10, 2018 Also if it's got a ballast wire, one end is on the ignition but the other may run to the starter solenoid rather than the coil. It does on mine. Doug Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 10, 2018 Report Share Posted May 10, 2018 yes Doug good call , thats a white and yellow bridges the resistive when cranking to boost the 6v coil with 12v so dont test the coil feed when cranking it will show as 12v. if its got one of these Pete Link to comment Share on other sites More sharing options...
Meeze Posted May 23, 2018 Report Share Posted May 23, 2018 Hi All My GT6 MKII with a MKIII engine misfired on the motorway last week, hot day and had to be towed off. At the same time, I noticed that my radiator had sprung a leak at the header tank. I have bought a new coil, plugs, cap, rotor arm & leads and already fitted a new radiator. I am due to fit the ignition stuff this weekend. In addition, my car has electronic ignition However, I have just read 'Cookies' comments about electric fans and mine has a revotec. I had this fitted as the temperature was getting too close for comfort a while ago on a hot journey. Cookie - are you against all electric fans? Any ideas would be great as I'm due to travel down to Lemans in July and this would be a holiday of a lifetime for me in EBY 876J Many thanks Maria Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 23, 2018 Report Share Posted May 23, 2018 Do you know the sorce of the initial missfire ? If youmstill have a ballasted coil feed is the electronic unit been set up witha bypassed 12v supply ?? If you have access to a meter can you check the coil feed voltage? You can check the feed voltage to the coil pos+ but may need to turn the engine as the unit has to be triggered or you will get a 12v reading , when on ballast its around 6-8volts An engine driven fan keeps a good air circulation under the bonnet all the time the engine is running, an electric comes on when the thermostat calls for operation, by then the under bonnet temp is already too high. Electric fans ,They are a love them hate them bit of kit, But cool air under the bonnet and a cold air supply to the carbs is essential, how thats achieved is do what triumph designed And tested comes to mind Pancake filters and stop start electric fans can often be a route to recovery required Pete Link to comment Share on other sites More sharing options...
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