1969Mk3Spitfire Posted June 14, 2021 Report Share Posted June 14, 2021 Occasionally, not always, my engine will run-on (for only 1 rev) after ignition is turned off. The engine is not above normal hot when it does this. There isn’t (shouldn’t be) any carbon build up in carbs nor combustion chamber. I use normal unleaded with additive. Idle is just under 1000 rpm, smooth running. Acceleration and running is normal. I don’t drive it hard. I’ve not yet checked ignition timing. Likely culprit? Link to comment Share on other sites More sharing options...
Steve P Posted June 14, 2021 Report Share Posted June 14, 2021 My 2.5 Vitesse only ever runs on if i have to put lower than Shell V Power 99 octane fuel in,it hates 95 or 97.Even with additive. Steve 1 Link to comment Share on other sites More sharing options...
johny Posted June 14, 2021 Report Share Posted June 14, 2021 Couple of things, the octane could be the problem and a lead substitute wont help that so either a higher octane fuel is needed or an octane booster. I use Millers VSPe with regular fuel and its very good at preventing any run on. The other thing is the spark plugs your using. What colour are the electrodes as if very white you could consider using cooler running ones so that they are less likely to cause ignition without a spark... Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 14, 2021 Report Share Posted June 14, 2021 running on often due to low grade fuel idle too fast wrong grade plugs retarded timing air leaks addatives breather problems heater fan motors left on . pete Link to comment Share on other sites More sharing options...
poppyman Posted June 14, 2021 Report Share Posted June 14, 2021 It can also be caused by turning the engine off to quick when you come to a stop, the rev's wont have died down and gives it the fast tickover problem as Pete mentions. Tony. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 14, 2021 Report Share Posted June 14, 2021 some permanent magnet blower motors act as a generator when you swich off so the engine gets some back feed power till the blower free wheels to a stop when forst introduced we had to ad a diode to kill the generation , on some trucks the ram effect would power the petrol engines with the ignition off. that was a fair while ago Pete Link to comment Share on other sites More sharing options...
johny Posted June 14, 2021 Report Share Posted June 14, 2021 yes I see modern cars have diodes for the electric radiator fans and AC compressors although I imagine today its to protect the electronics rather than prevent engine run on... Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 15, 2021 Author Report Share Posted June 15, 2021 Many thanks to you all, much appreciated. I'll certainly look at Millers VSPe additive. The plugs are NGK BP6ES and No 1 and No 4 probably look a tad lean. Picture attached. I've not checked the timing and I'd appreciate any tips. Check static or dynamic? It doesn't look easy (or safe) to get a strobe close-in. Haynes says 6 deg BTDC, static. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 15, 2021 Report Share Posted June 15, 2021 just use ears , with it idllng slacken dizzy clamp and turn the dizzy a small amount advance will speed up retarding will reduce idle so advance a little and test run it is not pinking under load , what fuel do you use it really needs 97+ or better and advance to give fastest idle but back it off form best as that will be too much advance lean and retarded gives very hot plugs and bits of carbon deposits that become a glow plug Pete Link to comment Share on other sites More sharing options...
poppyman Posted June 15, 2021 Report Share Posted June 15, 2021 Would advancing not cause more pinking Pete? Tony. Link to comment Share on other sites More sharing options...
Peaks Posted June 15, 2021 Report Share Posted June 15, 2021 I agree with the comments above; with my Vitesse running on occurs either because the timing is too advanced or the mixture is too lean. With a compression ratio of 9.75:1 (very slightly higher than standard) I've never found the need to run on super unleaded nor to use any additives. I'd start with checking for air leaks on he inlet side (wear in throttle spindles and emission valve are prime suspects), get your mixture right, then experiment with different timing settings on the road. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 15, 2021 Report Share Posted June 15, 2021 as these cars were made for running on 100+ ron 5* fuel thats surprising when the cars were designed 95ron 2* fuel was for side valves and motor mowers with a high CR you cant be getting the best from the engine i dont see the point of increasing th CR then running on low grade fuel surely all a bit counter productive ??? Pete Link to comment Share on other sites More sharing options...
johny Posted June 15, 2021 Report Share Posted June 15, 2021 4 hours ago, 1969Mk3Spitfire said: Certainly not running cold and if it was a BP5ES I would recommend a 6 however as it is think its better to try the other suggestions before considering a 7. The cooler you can get your engine to run also reduces the chances of run on and this of course is a combination of the engine conditions mentioned plus the efficiency of the cooling system.... If you let your engine tick over a while before turning off does that help? Link to comment Share on other sites More sharing options...
JohnD Posted June 15, 2021 Report Share Posted June 15, 2021 This such a common complaint, I wonder if there should be a fixed thread, or list of causes/solutions in this forum? To be updated with proven actions by some official keeper? Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 15, 2021 Author Report Share Posted June 15, 2021 @johny - interesting thought to let it idle a while before turning off. Not tried it but will. Thanks also for commenting upon the state of the plug. To be honest, I’m delighted that Nos 1 and 4 looked so similar. In 1976, when I last has a Spitfire, tinkering with the carbs was a weekly event. My current car seems more stable. Over run is not really a big issue and it only does it intermittently. I suspect low grade fuel is the biggest culprit. Read the comments re timing with interest. I don’t think I’ll touch it as it runs fairly well. It sounds like getting the timing right is as much an art as a science so I’ll leave well alone. @johnD - it is, if course, we’ll trodden territory and before posting I tried to use the search function but to no avail. It’s always good to hear anecdotes from those with lots of experience and a will to share. Link to comment Share on other sites More sharing options...
daverclasper Posted June 15, 2021 Report Share Posted June 15, 2021 Are those plug colours suggesting too weak?. After a cruise at around 3000 rpm for a good few miles (doesn't feel like it's running weak) and a plug chop, mine are a pale grey. I have heard that modern fuels give the grey colour, rather than brown?, though my plugs do give a darker/browner colour when at lower revs and also more stop and starts. Dave Link to comment Share on other sites More sharing options...
SpitFire6 Posted June 15, 2021 Report Share Posted June 15, 2021 Is it sparking on run on or is it electrics dead run on? Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 15, 2021 Report Share Posted June 15, 2021 well black is rich white is lean any colour in between providing the insulator is clean dosnt mean much other than its about right Pete 1 Link to comment Share on other sites More sharing options...
Peter Truman Posted June 15, 2021 Report Share Posted June 15, 2021 I know were talking sparkplugs, mixture & run on, my 68 Vitesse Mk2 has run on for the 51 years I've owned it & how many miles I've driven to check the plug colour I'd hate to think. I used to stop the run on by stalling the engine in gear using the clutch! around 5 years ago I gave up and fitted a solenoid to de-pressure the inlet manifold etal later emission reduction practice, ie solenoid shuts when ignition switched on and vents to atmosphere when ignition is switched off, there's a small filter on the solenoid vent. I use the Lucas solenoid but would prefer the all metal Ford type, I'll eventually find one. The downside it's another thing to check when the engine won't start ie has the solenoid shut! Link to comment Share on other sites More sharing options...
Clive Posted June 16, 2021 Report Share Posted June 16, 2021 On 14/06/2021 at 17:20, Pete Lewis said: some permanent magnet blower motors act as a generator when you swich off so the engine gets some back feed power till the blower free wheels to a stop when forst introduced we had to ad a diode to kill the generation , on some trucks the ram effect would power the petrol engines with the ignition off. that was a fair while ago Pete On 14/06/2021 at 18:20, johny said: yes I see modern cars have diodes for the electric radiator fans and AC compressors although I imagine today its to protect the electronics rather than prevent engine run on... I had that on both spitfires that have used modern ECUs to run. The backfeed from the alternator has to have a diode fitted, as there is just enough voltage to run the ecu. When I first fitted it, the solution was to press the brake pedal, the lights were enough to kill the voltage. I imagine any fan could do the same. But with the alternator issue the car will just run until the fuel is all gone. Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 16, 2021 Author Report Share Posted June 16, 2021 23 hours ago, Pete Lewis said: well black is rich white is lean any colour in between providing the insulator is clean dosnt mean much other than its about right Pete Seems like sage advice related to 50+ year old automotive engineering technology, thanks. Took the car out for a drive earlier today. Almost identical route and conditions to Monday. No over run when I turned-off the key. Is day-to-day variation one of the appeals of the marque 😃 Link to comment Share on other sites More sharing options...
johny Posted June 16, 2021 Report Share Posted June 16, 2021 No, I think you can get it so it never runs on but it may take a bit of perseverance doing one thing at a time until its solved 100%... Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 16, 2021 Report Share Posted June 16, 2021 if youre talking about the car ...dont let it listen they are crafty Pete Link to comment Share on other sites More sharing options...
daverclasper Posted June 17, 2021 Report Share Posted June 17, 2021 On 16/06/2021 at 17:49, 1969Mk3Spitfire said: Is day-to-day variation one of the appeals of the marque 😃 I have found that, and don't know why?. Link to comment Share on other sites More sharing options...
NonMember Posted June 17, 2021 Report Share Posted June 17, 2021 My Spitfire ran on (quite badly) the last time I drove it, which is unusual. However, it has a slow coolant leak and the level had got low, so the engine was unusually hot, which is a common trigger for running on. Link to comment Share on other sites More sharing options...
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