ron88 Posted August 30, 2014 Report Share Posted August 30, 2014 Hello everyone - I just got my 4A back from a full service and a day later - on starting - it ran very rough, backfiring frequently. I have an electronic dist and all the plugs are tight and unbroken. However, I tried it again today with the same problem - running rough and backfiring - but now with a small petrol leak at the union of the first float and the petrol pipe in from the pump. It's the only pipe are with a crimp clamp vs a screw one. So a steady slow leak. Could this be caused by a broken - or jammed - float in the first carb? (forcing some petrol backout through an ill fitting clamp??). Somehow there is improper flow to both or one carb = rough running. Don't know about the backfires, though. It runs so rough this is clearly now a self-repair first to get it back to the service shop in Acton. HS6 SU carbs on the car - rebuilt about two years ago. Thoughts welcome! Quote Link to post Share on other sites
Geko Posted August 30, 2014 Report Share Posted August 30, 2014 (edited) Firing order (1,3,4,2), broken dizzy cap, vacuum advance or float/needle jammed on one carb with fuel flooding the cylinders. Check those first but my guess is the last one. Black smoke ? Edited August 30, 2014 by Geko Quote Link to post Share on other sites
Revolution Posted August 31, 2014 Report Share Posted August 31, 2014 Yes, I'd check the carbs first especially if the garage cleaned out the petrol pump filter as part of the service......only takes a minute bit of sediment to work its way up the fuel pipe and jam the float needle Also, ask the garage if they tinkered with the carbs....balance/mixture adjustment.....could be running too lean if she backfires Don't forget the condensor, they can just pack up.....even a new one if the garage fitted a replacement as part of the service Cheers, Nick Quote Link to post Share on other sites
ron88 Posted August 31, 2014 Author Report Share Posted August 31, 2014 I've got an electronic distributor so no condensor and I was told timing as spot on. However the fuel filter (inline) was replaced. I know the air filters for the carbs were cleaned and re-oiled. I pulled the last plug (brand new) and it was black and slightly wet. That said no real black smoke. Have not taken the float apart for the chamber/float needle etc. I imagine that is my next stop when I have some time to play with it. Quote Link to post Share on other sites
Ashley James Posted August 31, 2014 Report Share Posted August 31, 2014 Is it spitting through the carburettors, which means running very weak or is it backfiring which will be an ignition issue. Possibly an electronic fault in the distributor. It'd be a condenser in a normal distributor. Quote Link to post Share on other sites
ron88 Posted August 31, 2014 Author Report Share Posted August 31, 2014 It is running rough. It maintains idle but roughly; any acceleration causes a backfire and it does not run any smoother. The distributor is an electronic 1-2-3 which has never given me a problem. Quote Link to post Share on other sites
ron88 Posted September 2, 2014 Author Report Share Posted September 2, 2014 Ok - getting a new pipe and clamp (to rule out any issues there) and will pop open the float chamber to see if the float and needle are clear. More details soon! Quote Link to post Share on other sites
RogerH Posted September 2, 2014 Report Share Posted September 2, 2014 Hi Ron, what did the garage do during the service. Did they attack the tappets at all - check these (backfiring!!) Have you checked the timing (back firing!!) Inlet manifold not tight Roger Quote Link to post Share on other sites
johnny250 Posted September 2, 2014 Report Share Posted September 2, 2014 Check that the jets are returning from the enrichment position, i.e. fully pushed up underneath both carbs, they get lowered when using the 'choke' and can stick in the down position. Quote Link to post Share on other sites
RogerH Posted September 2, 2014 Report Share Posted September 2, 2014 Hi Ron, have you checked for oil in the carb dash pots? Roger Quote Link to post Share on other sites
ron88 Posted September 3, 2014 Author Report Share Posted September 3, 2014 Thanks - a good "to do" list when I get to the car this weekend. I'm pretty sure the tappets were adjusted; timing was "spot on" I have been told. I have also been told the petrol leak is the "overflow" from the jammed float. (I will check as well). Report soon - and yes I do need to check for the oil. Lastly, both carbs seem ok in that the choke works as promised..... Quote Link to post Share on other sites
Ashley James Posted September 3, 2014 Report Share Posted September 3, 2014 It is running rough. It maintains idle but roughly; any acceleration causes a backfire and it does not run any smoother. The distributor is an electronic 1-2-3 which has never given me a problem. It might be timing but I suspect this is ignition and not carbs unless they're spitting back, rather than exhaust bangs. Quote Link to post Share on other sites
graeme Posted September 3, 2014 Report Share Posted September 3, 2014 Ron, I would have a very close look at the distributor cap, looking for a crack on the internal surfaces. You could also have a look at the running engine in the dark to see if there are any sparks where they shoudn't be. Cheers Graeme Quote Link to post Share on other sites
Tom Boyd Posted September 3, 2014 Report Share Posted September 3, 2014 Ron, I would call said garage that completed the work and tell them of your problems. Any garage worth there salt will send someone out to investigate. They may not if you have been tinkering yourself though Tom Quote Link to post Share on other sites
ron88 Posted September 4, 2014 Author Report Share Posted September 4, 2014 Thanks for that - I've spoken to them (garage) over the phone and they have suggested I look at the float myself. I'm ok to do that, as they will send out a length of pipe and a new clamp as a backup. If I have no success I'll look at other options. Re the distributor - it's a pretty new 123 electronic one. I haven't noticed any problem with cap or rotor, but will re-examine everything once I check on the float. I also need to see if there are clouds of blue smoke when started, which I haven't noticed before but will check for again. Quote Link to post Share on other sites
ron88 Posted September 10, 2014 Author Report Share Posted September 10, 2014 Ok, pulled the floats apart and the lines - blew through them and still had a rough runner with petrol leaking out or the first float. The garage guy came out on his bike and we tried again - this time no leak! We found one really fouled plug, cleaned it and ran it up slowly - less backfires. Next step is to take it out on the road...! **** - err....dirt in the first needle jet is the thought right now....It will get a good run Saturday. Quote Link to post Share on other sites
Revolution Posted September 10, 2014 Report Share Posted September 10, 2014 Ron Have you replaced any of the fuel pipe which leads from the fuel pump to the carbs? I did this and when I pushed home the pipe into the first float chamber inlet, really tiny fragments of rubber pipe kept finding themselves into the float chamber, blocking the jet causing flooding The car runs well at the moment but I keep expecting the same problem to reoccur Any fragments of crud coming from the fuel tank? I also put a fresh set of plugs in and it made a big difference to the starting and running Hope this helps, I'm sure it will be something simple! Nick Quote Link to post Share on other sites
ron88 Posted September 11, 2014 Author Report Share Posted September 11, 2014 Thanks Nick - the fuel lines are pretty new and the inline fuel filter brand new - the old one was pretty clear, too. The plugs were brand new a month ago but fouled at the moment. I'm going to clean them then run the car for a while. Seems to be solved but only a good run will tell that! Quote Link to post Share on other sites
Ashley James Posted September 12, 2014 Report Share Posted September 12, 2014 Backfires are nearly always condensers or electronic ignition, unless it's Lumenition. They have a build that blows and you stop. Quote Link to post Share on other sites
ron88 Posted September 13, 2014 Author Report Share Posted September 13, 2014 Ok, I nearly stalled on the flyover out of London today, lugging and backfiring. I gave it half choke and made it to the garage. Here we: 1) replaced the rotor on the 1-2-3 which was missing the interior metal clip, causing more play on the spindle; 2) replaced the jet in the front float as a precaution, and 3) replaced all plugs (2-3-4 very fouled). It runs OK now and I made it back over the "flyover". So, no real solution but clearly one of the above was the issue. I honestly think dirt in one of the jets followed fouled plugs. But, I'm getting an extra rotor in case! Quote Link to post Share on other sites
graeme Posted September 13, 2014 Report Share Posted September 13, 2014 If the car was backfiring then fuel was getting into the cyl but the firing was incorrect. No fuel = no back fire. I would guess that the rotor was at fault. Cheers Graeme Quote Link to post Share on other sites
marko Posted September 13, 2014 Report Share Posted September 13, 2014 Never use anything other than a Distributor Doctor "Red" rotor arm and NGK Plugs. Quote Link to post Share on other sites
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