salec Posted November 23, 2020 Report Share Posted November 23, 2020 Morning Chaps My TR4A's engine runs on after the ignition is switched off -- The carbs were completely refurbished 3000 Miles ago. It has Lumitron electronic ignition, new plugs, pretty much tried everything bar removing the head and de-coking. My classic car specialist (complete faith in his ability) has suggested a valve between the head and the carbs to flood the head with air on switch off as a fix ... I'm inclined to agree with him as having just spent a great deal on the clutch and gearbox I'm pretty much tapped out and don't want the expense of taking off the head etc. Anybody done anything similar? Any other suggestions as to what could be the problem. To my mind it has to be either fuel or ignition ... Open to anything. Steve Quote Link to post Share on other sites
rcreweread Posted November 23, 2020 Report Share Posted November 23, 2020 Steve - what fuel are you using - if not a premium fuel like Shell Optimax, BP Ultimate, Esso Premium or Tesco Momentum, try it and see if it makes a difference Cheers Rich Quote Link to post Share on other sites
peejay4A Posted November 23, 2020 Report Share Posted November 23, 2020 (edited) Tried the air valve trick, and about every other one. No joy. Probably due to my Burgess head mods. I now use IanC’s suggested solution. Foot brake hard down, 3rd gear, drag the clutch ever so slightly and switch off. Edited November 23, 2020 by peejay4A Quote Link to post Share on other sites
Geko Posted November 23, 2020 Report Share Posted November 23, 2020 I always suggest de-coking first, the water glass trick takes 10 min and lots of smoke Quote Link to post Share on other sites
stuart Posted November 23, 2020 Report Share Posted November 23, 2020 Recheck your ignition timing properly and float levels and then give it an Italian service. Stuart. Quote Link to post Share on other sites
stillp Posted November 23, 2020 Report Share Posted November 23, 2020 21 minutes ago, stuart said: Recheck your ignition timing properly and float levels and then give it an Italian service. Stuart. +1. I'd add check your valve clearances in case a hot exhaust valve isn't closing properly. What plugs are you using? Pete Quote Link to post Share on other sites
salec Posted November 23, 2020 Author Report Share Posted November 23, 2020 41 minutes ago, Geko said: I always suggest de-coking first, the water glass trick takes 10 min and lots of smoke Water glass trick ? ? ? What's that .... or am I being stupid? Quote Link to post Share on other sites
Quicksilver Posted November 23, 2020 Report Share Posted November 23, 2020 (edited) + 1 for fuel qualities and timing setup, (and it can also be a electric issue, is your ignition switch assembly in good order? this was the case by a friends MG A running on) Marcel Edited November 23, 2020 by Quicksilver Quote Link to post Share on other sites
iain Posted November 23, 2020 Report Share Posted November 23, 2020 ? Hot spot Iain Quote Link to post Share on other sites
Z320 Posted November 23, 2020 Report Share Posted November 23, 2020 please see this post On my experience - if you switch off the ignition - and the engine is running on, it doesn't matter how you adjust the ignition (which you switched of). Quote Link to post Share on other sites
Hamish Posted November 23, 2020 Report Share Posted November 23, 2020 Fuel quality. Quote Link to post Share on other sites
ianc Posted November 23, 2020 Report Share Posted November 23, 2020 I fitted an anti-run-on valve many years ago and I use top notch fuel, but I still get run-on and have done for years. The valve sits above and feeds straight into the inlet manifold's balance pipe. I pull the handbrake on hard (or press hard on the footbrake), select first gear then gently lift my left foot to slow the engine slightly as I turn the ignition OFF. Engine still wants to run on, but this regime quells it very rapidly. As the car runs very well, I cannot be bothered to investigate further - and I certainly would NOT remove the cylinder head! There are some things one just has to live with! Ian Cornish Quote Link to post Share on other sites
ntc Posted November 23, 2020 Report Share Posted November 23, 2020 22 minutes ago, Hamish said: Fuel quality. Spot on, I owned a 3000 miles from new 4 pot and it ran on, the fuel used today is far from what they was designed to use. Quote Link to post Share on other sites
john.r.davies Posted November 23, 2020 Report Share Posted November 23, 2020 This has been discussed before! Search here for "running on". 643 PAGES of discussion! Quote Link to post Share on other sites
Peter Cobbold Posted November 23, 2020 Report Share Posted November 23, 2020 Try a grade or two cooler plugs. Low octane of stale fuel can contribute. Taken from my IWE 2016 Tech Seminar: Quote Link to post Share on other sites
dingle Posted November 23, 2020 Report Share Posted November 23, 2020 Many years ago, I had the same problem with a TR4A. The pcv valve seemed to be the culprit. I remove it and reverted to the road draft tube of the earlier TRs. This, along with keeping the idle speed low, solved the issue. You might try temporarily plugging the pcv plumbing to see if this is the cause of your problem. Berry Quote Link to post Share on other sites
keith1948 Posted November 23, 2020 Report Share Posted November 23, 2020 Hello Steve I had this problem with my 4A for a while. Tried everything you have. Solution was to fit NGK BP7HS fast road plugs that run cooler than the standard BP6HS. Plug gap is 0.025inch. A cooler plug is less likely to cause run on after switching off the engine. Keith Quote Link to post Share on other sites
Z320 Posted November 24, 2020 Report Share Posted November 24, 2020 (edited) The TR makers missed (another time) the point when they had to change to a modern construction like other producers did: have a idle jet in the carbs and switch off the flow of air or the flow of petrol to the idle jet when switching off the ignition. That's all... Edited November 24, 2020 by Z320 my bad english writing + photo added Quote Link to post Share on other sites
ianc Posted November 24, 2020 Report Share Posted November 24, 2020 Keith - I've been running BP7HS, gapped 32 thou, since 1993. However, with a modified engine, I accept that "there are some things one just has to live with" (as I said before). It's difficult to set the tick-over much lower than 750-800 because the engine will tend to stall when the electric fan kicks in or if the alternator is having to power more than just the ignition. Ian Cornish Quote Link to post Share on other sites
john.r.davies Posted November 24, 2020 Report Share Posted November 24, 2020 Z320, Fantastic! That should make it go! Quote Link to post Share on other sites
Z320 Posted November 24, 2020 Report Share Posted November 24, 2020 Sorry, no, this makes it stop running immediately Quote Link to post Share on other sites
john.r.davies Posted November 24, 2020 Report Share Posted November 24, 2020 Then if they are not warp-factor electrodes, Z320, what are they?! Quote Link to post Share on other sites
Z320 Posted November 24, 2020 Report Share Posted November 24, 2020 (edited) Pierburg "idle switch off valve", they close when I switch 12 Volts on them by a push botton under the dash board. Mercedes Benz used them with Strombergs 175 CDT carbs on their M102 engine. I slightly modified them with DIY valve housings. That works lovely since 4 or 5 years. Edited November 24, 2020 by Z320 Quote Link to post Share on other sites
JeffR Posted November 27, 2020 Report Share Posted November 27, 2020 My TR4 started running on afew years ago. After trying all the usual things - timing, plugs etc I changed to using higher octane fuel such as BP Super or the Shell equivalent or Tesco Momentum. Since then ( several years ago) it's never run on - not even once! Cheers, JeffR Quote Link to post Share on other sites
salec Posted December 14, 2020 Author Report Share Posted December 14, 2020 Thanks to all of you .... I've just got the car back after a refurbed clutch, renewed gearbox and a valve to control the air flow when the engine is switched off, if I let the car idle for 30 seconds after a hot tub this seems to have done the trick, however I used higher octane fuel which seems to have helped. Thanks for all your comments, I will report back when I've done a few more miles. Steve Young PS pic is driving around the M25 last year. Quote Link to post Share on other sites
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