sandandlime Posted June 23, 2012 Report Share Posted June 23, 2012 Hi all, Since replacing the engine and gearbox mountings (very quickly followed by fuel pump failure) I have not been able to get Ludo running well. We have been backwards and forwards on all sorts of things without success and then, eventually, back to square one. By back to square one I mean: accurately determine tdc (using a soapy bubble) so that we know exactly where we are and set both carb jets to 38 thou down. Using a strobe we set the timing to 9° btdc at around 850 rpm only to find that performance was lacklustre and fuel consumption high. We then tried Andy's (67_gt6) 'dizzy' method (http://www.tr-register.co.uk/forums/index.php?showtopic=28937). That lead us to 13° btdc, better performance but with pinking and still having high fuel consumption. Today, we backed her off to 10° btdc at 1000 rpm and, after a 35 mile run, performance/economy seems much improved. We still, however, have issues which we have been chasing around for quite a while. What we are finding is that we set the tickover at 850 rpm reasonably well, albeit with some cycling of around +/- 100 rpm. After a short while into our test drive the tickover steadily begins to climb, up to about 1400 rpm. We stop at the side of the road, adjust back down and she's not too bad thereafter. When re-started again and whilst still warm she then refuses to tickover so we have to increase it again back to where we were. Another symptom that we find is that when taking your foot off to change gear, the revs 'hang', say 2500 rpm, before slowly dropping back. Driving wise, there are no signs of being lean and she pulls pretty well from 1800 rpm uphill without pinking. However, the plugs tell a different story. The photos are opposite sides of the same plug. One side looks fine the other way too lean; something is definitely not working as it should! Now, I'm well and truly stumped so if any wise person could suggest what to look at I'd be very appreciative. Tony Quote Link to post Share on other sites
Guest Mick RichardsChange... Posted June 23, 2012 Report Share Posted June 23, 2012 Check for inlet manifold air leaks, (spray brake cleaner through a narrow pipe around the carb insulation blocks and other joining areas) if the revs of the engine lift sharply thats where it's sucking air in. If not onto fix number 2. Mick Richards Quote Link to post Share on other sites
sandandlime Posted June 23, 2012 Author Report Share Posted June 23, 2012 Check for inlet manifold air leaks, (spray brake cleaner through a narrow pipe around the carb insulation blocks and other joining areas) if the revs of the engine lift sharply thats where it's sucking air in. If not onto fix number 2. Mick Richards Mick, I'll give it a go tomorrow and see what happens (I've got to do the grass today - or get a goat). Thanks for the tip. Tony Quote Link to post Share on other sites
Fireman049 Posted June 23, 2012 Report Share Posted June 23, 2012 Hi Tony ~ I'm really puzzled by the jets being set to .038" ~ I've tried this on my 2.2L TR3A and she refuses to idle at all. I have to unscrew the jets to about .056" (seven 'flats' down) before she'll idle properly. The ignition timing is 15 degrees BTDC. At these settings the engine will happily idle at about 350 ~ 400 rpm. Anyone else running their carbs. set to .038"? Tom. Quote Link to post Share on other sites
Icarus60 Posted June 23, 2012 Report Share Posted June 23, 2012 Hi Tony Couple of thoughts Are the needles centralised OK and does the piston drop with a positive click when it hits the bridge? I assume that the throttle shaft is repeatedly closing onto the stop and not sticking and the distributor is in good condition and A/R is working freely. Like Tom I have set the jets well below the 0.038 to get decent idle and performance. Mine are close to 0.055 ( I am well aware some people consider this to be too much). My H6s are in good rebuilt condition as is the engine. It wasn't until I richened to this figure that it started to perform satisfactorily. (The float levels are set as per the book) Best of Luck Rog Quote Link to post Share on other sites
Fireman049 Posted June 23, 2012 Report Share Posted June 23, 2012 Hi Rog ~ I've just come in from the garage. I reset the carbs. to .038" and she would have nothing to do with it ~ erratic running and a 'spitting' exhaust note and one hell of a backfire through the carbs. when I depress the accellerator! I screwed up the jets level with the 'bridge' and then unscrewed them seven 'flats' down ~ now she runs beautifully ~ it'll do nicely for me, thank you. The plugs are not 'sooted' up either. Tom. Quote Link to post Share on other sites
BrianC Posted June 23, 2012 Report Share Posted June 23, 2012 I'm afraid I can't help with solving the problem, but I would like to know how to measure the magic .038". i.e. Does one need a digital depth gauge or is it simply a question of counting the number of flats the jet nut is turned down from the bridge position and multiplying by the thread pitch? Secondly, is the magic number dependent on the exact carb and float type fitted and whether the float is set exactly as per the book. i.e. If the float is set higher or lower than recommended, does the magic number change accordingly? Finally (you'll be relieved to hear), does the magic number change if non-standard needles are fitted? [Apologies for the idiot questions, but in my youth I used to play about tuning carbs on my cars and never came across the scientific stuff - maybe that's why I spent so much time tweaking, but at least it kept me off the streets ] Quote Link to post Share on other sites
Fireman049 Posted June 23, 2012 Report Share Posted June 23, 2012 Brian ~ I used a digital vernier gauge which is 100% accurate. I would think that it would be impossible to guess the measurement. Tom. Quote Link to post Share on other sites
derekh Posted June 23, 2012 Report Share Posted June 23, 2012 I find that 38 thou down is about right with SM needles. Are you sure that the needles are correctly located in the pistons? Regards, Derek. Quote Link to post Share on other sites
Fireman049 Posted June 23, 2012 Report Share Posted June 23, 2012 Hi Derek ~ Yes, the needles are perfectly located in the pistons. Tom. Quote Link to post Share on other sites
Peter Cobbold Posted June 23, 2012 Report Share Posted June 23, 2012 (edited) I'm afraid I can't help with solving the problem, but I would like to know how to measure the magic .038". i.e. Does one need a digital depth gauge or is it simply a question of counting the number of flats the jet nut is turned down from the bridge position and multiplying by the thread pitch? Secondly, is the magic number dependent on the exact carb and float type fitted and whether the float is set exactly as per the book. i.e. If the float is set higher or lower than recommended, does the magic number change accordingly? Finally (you'll be relieved to hear), does the magic number change if non-standard needles are fitted? [Apologies for the idiot questions, but in my youth I used to play about tuning carbs on my cars and never came across the scientific stuff - maybe that's why I spent so much time tweaking, but at least it kept me off the streets ] Brian The minimum height of the top of the jet depends upon the diameter of the needle at that height when piston is fully down. The fuel flow at tick over is tiny so the annulus of fuel ( the area between the needle od and the jet bore) is equally tiny. But if the od and bore are the same no fuel can pass. When Tom adjusts his down until it runs right, he's done it right for the needle he uses. So there's no set point - do it by ear. ( the piston lifter pin is useful) The fuel level should be a few mm down from the bridge surface. Its not critical, but must not overflow. When air is passing through the carb the venturi suction is a fraction of 1psi ( 1psi is enough to lift 27 inches of water or more than 30" of petrol). So differences in fuel height of a few mm are neither here nor there, the venturi suction will easily pull the fuel up. Its that annulus that does the metering, and that depends upon the piston spring 'metering' the air flow and the needle/jet annulus the fuel. Peter Edited June 23, 2012 by Peter Cobbold Quote Link to post Share on other sites
sandandlime Posted June 23, 2012 Author Report Share Posted June 23, 2012 I find that 38 thou down is about right with SM needles. Are you sure that the needles are correctly located in the pistons? Regards, Derek. Hi Derek, I have wondered that but prefer to avoid taking everything apart just to put it back together again! As far as I can tell, the needles are in the right place and the pistons both fall with a satisfying clunk. As to what needles/jets they are - well, I'm not sure (I haven't taken the whole carb apart but feel that I may be coming to that stage). Peter mentioned float heights. Having checked the float bowls for crud etc I was surprised to note that he float heights are not adjustable. It seems that the plastic cones are designed to be no maintenance. Neither seem to have any leaks as far as I can tell. Being 'mildly modified' it may be that I am setting her too lean. However, she was set to 37 thou just before I started to change the engine mounts and running very well. The plugs may have suggested that she was a whisker on the lean side but it was so close it didn't deserve messing with. I did set them to 38 thou this time though just for the sake of it. As Tom said I also use a digital vernier to set the heights (I've tried counting flats but always seem to lose track or run out of fingers!) The only thing that's have wondered is could the behaviour that I'm seeing be due to an air lock in the cylinder head? having drained the block to allow me to change the mountings I've tried hard to get all of the air out of he system and topped it up twice. But old I have a pocket there thats causing one side of he block to be hotter than the other. I am mystified by the plugs being lean on one face and fine on the other - and they're all the same. I should be able to continue the investigation tomorrow. Thanks for your suggestions chaps, Tony Quote Link to post Share on other sites
BrianC Posted June 23, 2012 Report Share Posted June 23, 2012 When Tom adjusts his down until it runs right, he's done it right for the needle he uses. So there's no set point - do it by ear. ( the piston lifter pin is useful) Thanks Peter - seems I wasn't such a silly boy after all! It also confirms what the rolling road guy told me, that he doesn't waste time with factory settings but does it by ear with the aid of his tuning equipment analysers and probably getting on for half a century of tuning experience (much of it in racing/rallying). However, for us mortals, I guess the factory settings are a good starting point for small, incremental changes. Quote Link to post Share on other sites
Tr4Tony Posted June 23, 2012 Report Share Posted June 23, 2012 Tony When I built the car it was done so to run smoothly from 2500 rpm up to 6000, all power flat by 5200 rpm, so I really had no regard for slow running. Hence you will find the exhaust and carb needles etc set to run rich at tickover. If you want the car to run well at slow speed you will need to change the carb needles and the dizzy advance curve etc etc etc and a,so bear in mind that the carbs were last rebuilt in 1996 (properly by southern carbs in wimbledon) so may well be leaky as a post above. SU's do this, particularly if the engine is getting hot. Lastly, you may want to think about the cam that's in it. It's not too wild but again the slow speed running was not a feature. Similarly if the car isn't cooling properly anymore then no amount of tuning will be correct. You need to get the temperature steady at 3000 rpm and above to successfully get it sorted. Regards Tony Quote Link to post Share on other sites
Ashley James Posted June 23, 2012 Report Share Posted June 23, 2012 The plastic floats should be set so that 1/8th or 3mm drill fits between the lever on the float and face of the lid with it upturned. I've been using a vernier depth gauge to set the main jets down between 35-38 thou for forty odd years now and on every make of car with SUs and it works perfectly if everything else is set correctly as well. It's how all SUs were set in the factory and more accurate than by ear. My timing is set statically at 7 degrees, or by the timing marks on the fanbelt pulley. I'll be at Malvern and anyone can hear the tickover and pick up who's interested. Young Pete Cox tried it this week and was very complimentary indeed. Ash Quote Link to post Share on other sites
Icarus60 Posted June 23, 2012 Report Share Posted June 23, 2012 Brian If you haven't a digital caliper you might find that you can set the jet flush using the end of a six inch ruler and then wind the jet nut down and you should get 7 thou jet drop for each flat you adjust (or 0.042 per turn). So in Toms case above, his jets should be 0.049 down.when he turned the nut down by 7 flats. Mark the datum position on both nuts and ensure that they are both turned the same amount in any subsequent adjustments. With regard to your final question regarding changing needles the effect is basically nil at idle as most needles are the same diameter at the normal idle position ie right up next to the shoulder. If you go and buy that digital vernier you could check that this is true! Go on spoil your self they cost about two gallons of petrol now. Best Regards Rog Quote Link to post Share on other sites
Icarus60 Posted June 23, 2012 Report Share Posted June 23, 2012 Ash I knew this subject would get you attention. I do not share your experience on this issue. Many owners find that this magic number does not provide a magic solution and at least two have them have contibuted to this post. As a starting datum it is fine but nothing more than that IMHO. Regards Rog Quote Link to post Share on other sites
Ashley James Posted June 23, 2012 Report Share Posted June 23, 2012 I wish I had one of these cars to set up for the owner Quote Link to post Share on other sites
sandandlime Posted June 23, 2012 Author Report Share Posted June 23, 2012 Tony When I built the car it was done so to run smoothly from 2500 rpm up to 6000, all power flat by 5200 rpm, so I really had no regard for slow running. Hence you will find the exhaust and carb needles etc set to run rich at tickover. If you want the car to run well at slow speed you will need to change the carb needles and the dizzy advance curve etc etc etc and a,so bear in mind that the carbs were last rebuilt in 1996 (properly by southern carbs in wimbledon) so may well be leaky as a post above. SU's do this, particularly if the engine is getting hot. Lastly, you may want to think about the cam that's in it. It's not too wild but again the slow speed running was not a feature. Similarly if the car isn't cooling properly anymore then no amount of tuning will be correct. You need to get the temperature steady at 3000 rpm and above to successfully get it sorted. Regards Tony Hi Tony, Thanks for your input. I am in no doubt that my driving style is somewhat more tame than you envisaged when you rebuilt Ludo. However, its not always as 'domesticated' as it should be and since changing the mountings I no longer feel the need to 'drive like a girl,' as my son so succinctly puts it. One issue I do have though is that it's sometimes very hard driving through towns as, once hot, the tickover has increased and I find myself travelliing at 30 mph with my foot off the throttle and with accordngly lengthened stopping distances Whilst '96 is a way back now, the carbs still seem to be in good condition, although in need of a service due to the jets sticking occasionally when the choke is operated. I think that I'll drop the jets 10 thou, see if I can get a satisfactory tickover first of all. At the same time, I'll have another look at float heights as Ash suggests before giving her a blast and seeing what else happens. Thanks for your help again and best regards, Tony Quote Link to post Share on other sites
Peter Cobbold Posted June 23, 2012 Report Share Posted June 23, 2012 Thanks Peter - seems I wasn't such a silly boy after all! It also confirms what the rolling road guy told me, that he doesn't waste time with factory settings but does it by ear with the aid of his tuning equipment analysers and probably getting on for half a century of tuning experience (much of it in racing/rallying). However, for us mortals, I guess the factory settings are a good starting point for small, incremental changes. Brian With a £150 wideband AFR sensor in the exhaust and a means to measure piston lift its now possible, unlike the old days, to set up the carbs as good as a rr with specialist equipment can give. The classic measure of piston lift was to fit a dowel - but that cant be seen with bonnet shut. So a fibreoptic camera looking at the piston from the filter side should do the job. One day I'll get round to it......factory settings don't exist for my setup. Peter Quote Link to post Share on other sites
sandandlime Posted June 24, 2012 Author Report Share Posted June 24, 2012 Thank you to all for your input and tips. I've had the chance to carry on probing the issue today and started by checking for vacuum leaks and dropping the jets 10 thou to 48 thou. Timing set to 11° and tickover around 850 rpm, certainly less cycling and idling reasonably steady. Also took the opportunity to check the needles as clearly, with the jets sticking when the choke is pulled, it is a good idea to service the carbs sooner rather than later. Both needles, marked SM, look okay although there is some minor scratching on the front one. When I order the service kit I'll also get a couple of new needles - but which ones are advised for touring rather than a performance emphasis, SM or TW? After a long and careful examination, the only thing that I could see that didn't look right was that the bridge on the font carb was wet whilst the rear was dry. So check the floats. The plastic floats should be set so that 1/8th or 3mm drill fits between the lever on the float and face of the lid with it upturned. As I mentioned earlier, as far as I can see there is not scope for float adjustment on these carbs. Just a plastic moulding sitting directly on the needle and hinged at the rear. I've also got an Alvis TA14 with a single Type H SU and this has an adjustable metal yoke to enable float height to be set but nothing similar here. Also, Burlens' replacement floats seem to be of the same fixed height design - only the 'stay up' alternatives have adjustment, even if by rather delicate looking metal arms. Have I missed something here? Having got everything back together again I then took her out for a spin of around ten miles of mixed driving, up to 80 mph for a while and then as Mr Sensible. She drove well but the idle revs still picked-up, although only to around 1200 rpm. Might this be due to setting the idle without air filters and then enriching the fuel/air ratio by refitting them before going out? Once I got back the first thing that I did was to check the plugs - they all look pretty much the same and definitely too white. So I'm back to wondering about air being trapped in the cylinder head. To investigate this I've lifted the front onto axle stands and intend to run her without the radiator cap once she's cooled down enough for me to remove the cap without being sprayed. Any other suggestions very gratefully received. TIA, Tony Quote Link to post Share on other sites
Guest Mick RichardsChange... Posted June 25, 2012 Report Share Posted June 25, 2012 Tony, How did the air leak test progress ? Mick Richards Quote Link to post Share on other sites
Ashley James Posted June 25, 2012 Report Share Posted June 25, 2012 As someone has already suggested, it's worth making sure the jets are centred correctly and the the pistons drop right down with a clunk and also, using a feeler gauge under the throttle butterflies, make sure they open at exactly the same time. Nothing will work correctly if fuel is trickling through because the needles in the float chambers are leaking. The floats in the HS6s in my Healey have bendable metal straps riveted to the top and the manual gives the 3mm clearance. I assumed the TR was the same. Sorry. However, if you remove the dashpots you'll see if fuel is spilling over the bridge and if not, if the fuel level is just below the top of the jet. Ash Quote Link to post Share on other sites
Guest ntc Posted June 25, 2012 Report Share Posted June 25, 2012 Can any of you Guys remember the simple bridging plate with cut out that they used to use? easy to make Quote Link to post Share on other sites
Icarus60 Posted June 25, 2012 Report Share Posted June 25, 2012 Tony As you have experienced an improvement by richening by 1 1/2 flats why not try some more. Why not drop them to 0.060 and approach further adjustment from the rich side and see how it goes. Do you have HS6 on your TR and H6 on your Alvis. I think you can shim the brass needle housing threaded portion on the HS6 but Ive never done this - mine are H6 with the fuel feed cast as part of the float bowl rather than a flexible pipe. As a priority I would sort out any sticking jets first though. All the best Rog Quote Link to post Share on other sites
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