coxy123 Posted June 11, 2023 Report Share Posted June 11, 2023 Triumph spitfire 1500 Hot a bad misfire/stutter at lower speeds/revs. At higher speeds it runs great Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 12, 2023 Report Share Posted June 12, 2023 there can be a wide variety of culprits spark plugs no R suffix and plugs life and soul of the engine many dont last well points check the gap damper oil top it up use engine oil is it over advanced ? tight valve clearances choked air cleaner and a must chech the choke is returning the jet to its adjusting nut give the jet a poke with the finger followed by as a 1500 do you still have waxstats on the jet easy to peen open the case remove the wax capsule, add two 1p peices and the small metal spacer refit the case Pete Link to comment Share on other sites More sharing options...
coxy123 Posted June 12, 2023 Author Report Share Posted June 12, 2023 Hi Pete I've got electronic ignition. The dampers seem low on oil I changed the waxstat for pennies. I haven't checked plugs or air filters Link to comment Share on other sites More sharing options...
coxy123 Posted June 12, 2023 Author Report Share Posted June 12, 2023 It was all a bit hot after coming home from Silverstone Link to comment Share on other sites More sharing options...
chrishawley Posted June 12, 2023 Report Share Posted June 12, 2023 11 hours ago, coxy123 said: Triumph spitfire 1500 Hot a bad misfire/stutter at lower speeds/revs. At higher speeds it runs great Might there be any clues from the history of the problem? Is this a problem which has appeared suddenly, developed over the course of time or been a constant factor following some other event (e.g. engine work, carb rebuild etc)? A per Pete's reply there's certainly a rather long list of potential diagnoses. Most of which are non-serious but can be effortful to track down. But to start somewhere I'd opt for simple inspections and measures first e.g. • Wires to/from coil: check good, not corroded or frail • Distributor: Inspect points (if applicable), rotor arm, distributor cap for defects. Check vacuum advance line is secure at distributor end and carburettor end. • Fuel line from pump to carbs: inspect for weeping or leaks • Carburettors; check dashpots have sufficient oil. Check all linkages, including choke mechanism, all operate and return smoothly. Lubricate in any case. Check heatshield between carbs and inlet manifold is present and intact. Check breather pipes from rocker cover to carbs are secure and free from even the tiniest splits or leaks. • Check fan. With engine OFF (of course!) spin fan with finger. if spins freely, without resistance, the viscous coupling may have failed. • Lastly, remove sparks plugs, check are correct specification for vehicle, observe condition and colour of each, check gap. Siimple inspections might be suggestive of diagnosis, if not then more in-depth measures could be needed. Link to comment Share on other sites More sharing options...
cliff.b Posted June 12, 2023 Report Share Posted June 12, 2023 (edited) Just one more thing, based on my own recent experience, is there any smoke when it is misfiring/stuttering? If so, what colour? I had the same symptoms with white smoke and it was my head gasket blown, cylinder to water gallery. Ran fine at speed but forced coolant into overflow bottle. Edited June 12, 2023 by cliff.b Spelling Link to comment Share on other sites More sharing options...
AlanT Posted June 12, 2023 Report Share Posted June 12, 2023 If it's when hot then I'd wager some form of vapourisation. I had a Spit 1500 (years ago) that every garage failed to spot was missing the heat shield that goes between carbs and manifold. It's vital that this is in good condition or the car won't run right on hot days (like this past weekend). Higher speeds are fine since the air flow is sufficient to cool the carbs. It's at lower speeds that issues arise. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 12, 2023 Report Share Posted June 12, 2023 do check the coil is wired polarity correct many get reversed that can cause grief neg to diizy pos to coil + Pete Link to comment Share on other sites More sharing options...
DerekS Posted June 12, 2023 Report Share Posted June 12, 2023 What air filters are you using, standard with standard airbox, or the K+N types? Derek. Link to comment Share on other sites More sharing options...
coxy123 Posted June 13, 2023 Author Report Share Posted June 13, 2023 Standard air filters. I checked dashpots last night, they had hardly any oil in them. I haven't tested it yet but I'm thinking this is the problem Link to comment Share on other sites More sharing options...
johny Posted June 13, 2023 Report Share Posted June 13, 2023 Hmmm the oil is to enrichen the mixture on acceleration so shouldnt make much difference at steady revs at any speed... Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 13, 2023 Report Share Posted June 13, 2023 but will give you flat spots on any change of throttle empty dashpots is not allowed here you know Ha !! let us know if it solves the problem Pete Link to comment Share on other sites More sharing options...
Chris A Posted June 13, 2023 Report Share Posted June 13, 2023 1 hour ago, Pete Lewis said: empty dashpots is not allowed here you know Ha !! Is this going to lead to the 'what oil' question? 🤔 Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 13, 2023 Report Share Posted June 13, 2023 I really really hope not Ha ! Link to comment Share on other sites More sharing options...
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