pinky Posted May 18, 2019 Share Posted May 18, 2019 Hi, I am having a problem on start up, the engine starts, but bangs cracks pops in the exaust pipe, When the engine warms this stops, I recon on to much air getting in some were, then when warm expands and stops Or could it be blocked jefs in the carb Running on webber's, and 123 unit What do you think Thanks pink Link to comment Share on other sites More sharing options...
JohnD Posted May 18, 2019 Share Posted May 18, 2019 pinky, Fuel burning in the exhaust pipe casing such effects cannot have fully burnt in the chamber. So insufficient fuel due to blocked jets seems unlikely. A very weak mixture might burn so slowly to cause that, but more likely IMHO is a missfire. John Link to comment Share on other sites More sharing options...
pinky Posted May 18, 2019 Author Share Posted May 18, 2019 Thanks John, listening to the engine it appears to be running ok, the banging is exstremly load until it warms up, Could it be air getting in Cheers pink Link to comment Share on other sites More sharing options...
richy_rich Posted May 19, 2019 Share Posted May 19, 2019 Does it misfire at higher revs, or just at cold idle? As it's Weber carbs I assume you're not using any choke? As John says banging in the exhaust is usually unburned fuel, with Webers I'd guess that your idle settings are too rich. Link to comment Share on other sites More sharing options...
Nick Jones Posted May 19, 2019 Share Posted May 19, 2019 Has it always done this or is it a new thing? Definitely banging in the exhaust or spitting back through the carb throats? As it happens cold but not warm as Weber’s rarely have their chokes connected l’m thinking either spitting back or lean misfire in one or two cylinders with the unburned mix being lit in the exhaust by the firing cylinders. TR or DeTomasso? Link to comment Share on other sites More sharing options...
Neil T Posted May 19, 2019 Share Posted May 19, 2019 For it to come on just like that take your pick, Misab plates/washer shot or not set correct Rotor arm tracking 123 common problem Coil Leads Link to comment Share on other sites More sharing options...
PeterC Posted May 19, 2019 Share Posted May 19, 2019 Tracking in disy cap allowing a plug to fire when a valve is open ? Link to comment Share on other sites More sharing options...
pinky Posted May 19, 2019 Author Share Posted May 19, 2019 Thank you gentlemen I will put to practice what you have suggested to tomorow, No choke used When warm it stops This has just started, definatly in the exaust pipe and spitting back through the carbs Been to bulie today, so havnt had a chance to have look Thank you for your advise Pink Link to comment Share on other sites More sharing options...
RedRooster Posted May 19, 2019 Share Posted May 19, 2019 My bet is rotor arm, is it a proper one or Chinese? RR Link to comment Share on other sites More sharing options...
Nick Jones Posted May 19, 2019 Share Posted May 19, 2019 1 hour ago, RedRooster said: My bet is rotor arm, is it a proper one or Chinese? RR Only happening cold....? These are usually worse when hot. Most ignition issues seem to be worse when hot. I think the Misab plates / O-rings is a very good call. Small air leak making it very lean when cold and a bit less lean when warm...... Link to comment Share on other sites More sharing options...
pinky Posted May 20, 2019 Author Share Posted May 20, 2019 Thank you for all your replays, Cleaned all the jets, Checked ht leads all ok Replaced the distributor cap, thing improved had 2 more bangs then ok, the cap is a buro Now maybe by this time it had wamed up, so I will try again tomorow, The first carburetor spits back, so maybe I need to replace the thackeray washers to Cheers Pink Link to comment Share on other sites More sharing options...
pinky Posted May 21, 2019 Author Share Posted May 21, 2019 My apologies, not the distributor cap I replaced the rotor arm, it's a buro Link to comment Share on other sites More sharing options...
pinky Posted May 21, 2019 Author Share Posted May 21, 2019 Well thank you for all your help , Did all the things you suggested, nothing, so sat back and thought about it a few years ago I changed the plugs on a motorbike , Run for a while then stopped went over every thing, changed the plugs, bingo, sorted So I did this on the 6 changed all the plugs bingo running a treat now, so what happens to the plug when it goes tits up and is there any way of finding g wich plug it was Cheers pink, thanks for your help Link to comment Share on other sites More sharing options...
JohnD Posted May 21, 2019 Share Posted May 21, 2019 Which confirms several opinins above - misfire! Unburnt fuel burning in the exhaust. Ignited by hot exhaust, + glowing carbon from previous late burns. John Link to comment Share on other sites More sharing options...
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