Z320 Posted June 13, 2021 Report Share Posted June 13, 2021 (edited) Hi there, my TR has some "jerking" when driving between low ecceleration and the eccelerator released. My impression is it's getting worse from year to year. Can a poor shimed diff be the issue? I know it has some play. Ciao, Marco Edited October 29, 2023 by Z320 Quote Link to post Share on other sites
Drewmotty Posted June 13, 2021 Report Share Posted June 13, 2021 I’ve had a similar issue on my TR3 for some years and failed to find the culprit. My TR4 doesn’t have the issue even though the diff has far more free play so I don’t the that the diff can be the problem. Quote Link to post Share on other sites
stuart Posted June 13, 2021 Report Share Posted June 13, 2021 Sometimes an over adjusted throttle control can do this, it’s good to have a little free play on the linkage. Stuart Quote Link to post Share on other sites
Z320 Posted June 14, 2021 Author Report Share Posted June 14, 2021 Good morning Stuart, the TR4A linkage is special but installed and adjusted correctly. But indeed it does not give the "forks" of the carbs free (no gap) anymore, I can force it gently and hope WD40 does the job until I'm back from office this evening. I can't believe this is the reason, but if it is I will be very pleased. Thank you, Marco Quote Link to post Share on other sites
Z320 Posted June 14, 2021 Author Report Share Posted June 14, 2021 8 hours ago, Drewmotty said: I’ve had a similar issue on my TR3 for some years and failed to find the culprit. My TR4 doesn’t have the issue even though the diff has far more free play so I don’t the that the diff can be the problem. Hi Drewmotty, thank you at least for that comparison. Ciao, Marco Quote Link to post Share on other sites
BlueTR3A-5EKT Posted June 14, 2021 Report Share Posted June 14, 2021 I get similar 'kangaroo petrol' issues at slow speed in first gear with light throttle pressure. - almost as if I am learning to drive again! My car has cable throttle to the SU carbs so I am not able to do proper comparison to yours with rod linkage. Peter W Quote Link to post Share on other sites
stuart Posted June 14, 2021 Report Share Posted June 14, 2021 Its very obvious when travelling the lane into my workshop as its not very smooth and as the throttle pedal on the TR is a pendulum type your balancing on the heel and pressing with the front part of your foot so its not that easy to be subtle with pressure applied. If theres no free play in your linkage then you will get jerky application. I found it particularly obvious when I first fitted the Dellortos to mine as I had to make up a new mechanism from scratch and rather than going down the cable route I opted for a version of the usual rod links, the first version was far too direct and so I had to add some slack into the system and now its very smooth. HS6 have forked linkages for the self same reason to allow some free play. Stuart. Quote Link to post Share on other sites
ctc77965o Posted June 14, 2021 Report Share Posted June 14, 2021 What's your ignition ? Still using centrifugal advance?? Maybe your weights are sloppy? Quote Link to post Share on other sites
Z320 Posted June 14, 2021 Author Report Share Posted June 14, 2021 Hi Stuart, it seems to be less jerking now - but maybe it is only my wish....? Not only the linkage has s return spring, both forks on the SUs two...and they always worked. Hi Dave, I use an original distributor, last year with points, this year with a Pertronix Ignitor I, this seems to work better - but maybe this is only what I wish...? Damper oil is OK, mixture is rich, spark plugs are lovely "dark".... Quote Link to post Share on other sites
Z320 Posted June 15, 2021 Author Report Share Posted June 15, 2021 Hi, this is my measurement from yesterday evening I can turn the diff flange about 5 mm from stop to stop, this is about 7° play on the 79.50 mm circle. The pinion has 10 tooht x 36°? And I have 7° play? Quote Link to post Share on other sites
Drewmotty Posted June 15, 2021 Report Share Posted June 15, 2021 I’ve finally spent half a day converting my TR3 to a cable throttle and it’s made a huge improvement to the kangarooing on bumpy lanes at low throttle. The car now behaves at least as well as my TR4 which has always been fine with the standard setup. That said I still haven’t been able to identify a root cause to the problem. Quote Link to post Share on other sites
Drewmotty Posted June 15, 2021 Report Share Posted June 15, 2021 7 hours ago, Z320 said: Hi, this is my measurement from yesterday evening I can turn the diff flange about 5 mm from stop to stop, this is about 7° play on the 79.50 mm circle. The pinion has 10 tooht x 36°? And I have 7° play? I’ve got more than that on my TR4 which doesn’t suffer with jerky response. Quote Link to post Share on other sites
Peter Cobbold Posted June 15, 2021 Report Share Posted June 15, 2021 On 6/14/2021 at 8:50 AM, BlueTR3A-5EKT said: I get similar 'kangaroo petrol' issues at slow speed in first gear with light throttle pressure. - almost as if I am learning to drive again! My car has cable throttle to the SU carbs so I am not able to do proper comparison to yours with rod linkage. Peter W Peter, Might be weak mixture. Weak mix burns slow> rpm falls> mixture richens > burns better > rpm rise >mixture weakens................ Test is to try a little choke. Or lower the jets. Tick over mixture is normally very rich but a manifold air leak can weaken it. Peter Quote Link to post Share on other sites
stuart Posted June 15, 2021 Report Share Posted June 15, 2021 43 minutes ago, Drewmotty said: I’ve finally spent half a day converting my TR3 to a cable throttle and it’s made a huge improvement to the kangarooing on bumpy lanes at low throttle. The car now behaves at least as well as my TR4 which has always been fine with the standard setup. That said I still haven’t been able to identify a root cause to the problem. Have you set the clearance on the throttle forks? Stuart. Quote Link to post Share on other sites
Drewmotty Posted June 15, 2021 Report Share Posted June 15, 2021 They were already set and remain unchanged. Chilliman has come up with an interesting theory: weak return springs. Sounds plausible especially when the mass of the operating rod is considered as it moves directly backward and forwards. I’m not in a position now to double up on springs to test the theory but it wouldn’t take long to test. Maybe give it a try Marco. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted June 15, 2021 Report Share Posted June 15, 2021 (edited) 3 hours ago, Peter Cobbold said: Peter, Might be weak mixture. Weak mix burns slow> rpm falls> mixture richens > burns better > rpm rise >mixture weakens................ Test is to try a little choke. Or lower the jets. Tick over mixture is normally very rich but a manifold air leak can weaken it. Peter Thank you Peter, I will drop the jets a flat each and see if it changes things. I had also wondered about piston flutter with the different piston dampers that are available. I run the AUC 8114 not AUC 8103 type. The 8114 having more clearance for the piston to move before the damper comes into full effect. Perhaps I need to swap the dampers to test….. Cheers Peter W Edited June 15, 2021 by BlueTR3A-5EKT Quote Link to post Share on other sites
Z320 Posted June 15, 2021 Author Report Share Posted June 15, 2021 Sadly the return springs work well, giving the linkage free you can hear a "click" when the U-forks are touching the adjusting screw Quote Link to post Share on other sites
BlueTR3A-5EKT Posted June 15, 2021 Report Share Posted June 15, 2021 (edited) 4 hours ago, Drewmotty said: I’ve finally spent half a day converting my TR3 to a cable throttle and it’s made a huge improvement to the kangarooing on bumpy lanes at low throttle. The car now behaves at least as well as my TR4 which has always been fine with the standard setup. That said I still haven’t been able to identify a root cause to the problem. Might I suggest you add a couple of cable terminal covers to your battery to solenoid cables. That choke cable would make a lovely conductor to earth if it touched the solenoid cables. Peter W https://www.autoelectricsupplies.co.uk/product/159/category/32 PS Be sure to carry a spare throttle cable and method of fitting. I tuck my spare behind the accelerator cable bracket. Edited June 15, 2021 by BlueTR3A-5EKT Quote Link to post Share on other sites
Drewmotty Posted June 15, 2021 Report Share Posted June 15, 2021 I’d press the “Like” button Peter but we’ve lost it. :-) Quote Link to post Share on other sites
Peter Cobbold Posted June 16, 2021 Report Share Posted June 16, 2021 9 hours ago, BlueTR3A-5EKT said: Thank you Peter, I will drop the jets a flat each and see if it changes things. I had also wondered about piston flutter with the different piston dampers that are available. I run the AUC 8114 not AUC 8103 type. The 8114 having more clearance for the piston to move before the damper comes into full effect. Perhaps I need to swap the dampers to test….. Cheers Peter W Peter, Peter, Could it be a leaking over-run valve in one of the butterflies ? - though these were later fitments I think, not used on TRs until the 7. Peter Quote Link to post Share on other sites
Peter Cobbold Posted June 16, 2021 Report Share Posted June 16, 2021 9 hours ago, BlueTR3A-5EKT said: Thank you Peter, I will drop the jets a flat each and see if it changes things. I had also wondered about piston flutter with the different piston dampers that are available. I run the AUC 8114 not AUC 8103 type. The 8114 having more clearance for the piston to move before the damper comes into full effect. Perhaps I need to swap the dampers to test….. Cheers Peter W Peter, In first gear crawl there should not be any pulsing of air pressure at the piston or jet as the butterflies are barely cracked open. At less than 30deg opening the flow past the butterfly is sonic and iv pressure pulses cannot pass. So I would not suspect dampers to be operating. Peter Quote Link to post Share on other sites
BlueTR3A-5EKT Posted June 16, 2021 Report Share Posted June 16, 2021 2 hours ago, Peter Cobbold said: Peter, Peter, Could it be a leaking over-run valve in one of the butterflies ? - though these were later fitments I think, not used on TRs until the 7. Peter Overrun valves were fitted to the carbs that are on my car. I snipped them out and filled the holes in the butterflies with solder many years ago so that is one item off the list. The possibility of an air leak could be worn spindles. The carbs were new in 1975. Will do a spray test with the engine running. Thanks. Peter W Quote Link to post Share on other sites
ctc77965o Posted June 16, 2021 Report Share Posted June 16, 2021 As the Americans say: "carburetor is a French word meaning DO NOT TOUCH" : look at the ignition first... Quote Link to post Share on other sites
Z320 Posted June 16, 2021 Author Report Share Posted June 16, 2021 Today I put the air filters off, the dampers do not work on the first 3-4 mm (I guess, not measured), I realize this is "the empty way" of the damper and it is out of function while idling. Is this correct? I can lift the pistion without much force only against their weight and the spring inside. Should I use other springs? Also I pressed the pin up to lift the pistons while ideling: revs increase, than fall lower than before. Means: the mixture is too week? But the spark plugs are black. I should try hoter ones? Quote Link to post Share on other sites
Hamish Posted June 17, 2021 Report Share Posted June 17, 2021 10 hours ago, Z320 said: Today I put the air filters off, the dampers do not work on the first 3-4 mm (I guess, not measured), I realize this is "the empty way" of the damper and it is out of function while idling. Is this correct? I can lift the pistion without much force only against their weight and the spring inside. Should I use other springs? Also I pressed the pin up to lift the pistons while ideling: revs increase, than fall lower than before. Means: the mixture is too week? But the spark plugs are black. I should try hoter ones? I know this says mg but they are SU carbs and this guy knows his classics and shares his knowledge Quote Link to post Share on other sites
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