JohnTB Posted June 7, 2011 Report Share Posted June 7, 2011 Can anyone please tell just what 'Butterfly Fluter' is. How does it manifest itself ? This is the context of an original Lucas injection system on a CP TR6. Quote Link to post Share on other sites
Peter Cobbold Posted June 7, 2011 Report Share Posted June 7, 2011 Never heard it mentioned before. But it could be the result of the air flow in each manifold naturally pulsing as the inlet valve opens and closes. If the small springs that fit over the ends of the butterfly spindles are missing or perhaps weak then the butterflies might flutter.... but I have my doubts. Who told you about it? Quote Link to post Share on other sites
JohnTB Posted June 7, 2011 Author Report Share Posted June 7, 2011 Never heard it mentioned before. But it could be the result of the air flow in each manifold naturally pulsing as the inlet valve opens and closes. If the small springs that fit over the ends of the butterfly spindles are missing or perhaps weak then the butterflies might flutter.... but I have my doubts. Who told you about it? "" Seen it quoted with respect to Revington overhead throttle linkage as "...... eliminates Butterfly flutter...." I currently get what can only be described as a "roughness" on deceleration (when all the butterfly's will be fully closed). If a give a very slight pressure on the accelerator (not enough to affect the deceleration) thus slightly opening the butterflys, this "roughness" stops. The car is pretty well set up, gives around 30mpg and is reasonably sprightly. Tickover 'enjoys' the usual Lucas lumpiness. Quote Link to post Share on other sites
Steves_TR6 Posted June 7, 2011 Report Share Posted June 7, 2011 The car is pretty well set up, gives around 30mpg and is reasonably sprightly. Blimey, 30 mpg. Those butterflies fluttering must be a good thing ! Quote Link to post Share on other sites
JohnTB Posted June 7, 2011 Author Report Share Posted June 7, 2011 Blimey, 30 mpg. Those butterflies fluttering must be a good thing ! The 30mpg was the round trip (700 miles) to Laon Historic last weekend. Guess a little less on more local journeys, but still pretty good. Any advice on the 'fluttering" much appreciated. Quote Link to post Share on other sites
Peter Cobbold Posted June 8, 2011 Report Share Posted June 8, 2011 "" Seen it quoted with respect to Revington overhead throttle linkage as "...... eliminates Butterfly flutter...." I currently get what can only be described as a "roughness" on deceleration (when all the butterfly's will be fully closed). If a give a very slight pressure on the accelerator (not enough to affect the deceleration) thus slightly opening the butterflys, this "roughness" stops. The car is pretty well set up, gives around 30mpg and is reasonably sprightly. Tickover 'enjoys' the usual Lucas lumpiness. John On the overrun - ie deceleration with throttles closed - the petrol flow will do whatever the fuel cam was set up to provide by the supplier - without an exhaust probe for AFR we can only guess. But I reckon your engine is running rich when there is very low pressure in the manifold. This is NOT an MU fault ( that 30mpg is good). But the closed butterflies could be so well fitting as to close off virtually all air flow. This means that on some cycles the plug fails to ignite the flame and unburned mixture gets into the exhaust, where it is ignited by residual flame from another cylinder firing. On original TR6 PIs those popping backfires in the exhaust was a very distinctive sound! The tick-over may also be a little air-deficient, and again cycle-by-cycle variations in combustion cause the uneveness. If you can't live with the classic TR6PI sound answer I think is to allow a tad more air past the butterflies when they are shut. On the CR manifold that was done with the air valve. On CP you'll need to adjust the closed setting to open the butterflies very slightly. Peter Quote Link to post Share on other sites
JohnTB Posted June 8, 2011 Author Report Share Posted June 8, 2011 Thank you Peter, This makes sense. I will be fitting the Revington overhead throttle control in the morning and in view of what you say, I will set up so that the butterfly's are slightly open at tickover and then close off the air bleed valve. I do know that the air valve being at the front can lead to air starvation at the rear two cylinders and there is in fact a remedy described on the TR Register technics CD. So it does make sense to ensure that each of the throttles have their own air supply when "closed" Quote Link to post Share on other sites
smizgals Posted June 9, 2011 Report Share Posted June 9, 2011 (edited) John On the overrun - ie deceleration with throttles closed - the petrol flow will do whatever the fuel cam was set up to provide by the supplier - without an exhaust probe for AFR we can only guess. But I reckon your engine is running rich when there is very low pressure in the manifold. This is NOT an MU fault ( that 30mpg is good). But the closed butterflies could be so well fitting as to close off virtually all air flow. This means that on some cycles the plug fails to ignite the flame and unburned mixture gets into the exhaust, where it is ignited by residual flame from another cylinder firing. On original TR6 PIs those popping backfires in the exhaust was a very distinctive sound! The tick-over may also be a little air-deficient, and again cycle-by-cycle variations in combustion cause the uneveness. If you can't live with the classic TR6PI sound answer I think is to allow a tad more air past the butterflies when they are shut. On the CR manifold that was done with the air valve. On CP you'll need to adjust the closed setting to open the butterflies very slightly. Peter Quote from post http://www.tr-register.co.uk/forums/index.php?showtopic=24875&st=0&p=178305&hl=backfire&fromsearch=1entry178305 last year: 'I have just spoken to Malcolm, Prestige, who re-calibrated the MU, and he has asked me to increase the minimum fuel supply with the adjuster under the cap on the MU. The reason, in my words, is that my Phoenix extractor manifold is running hotter than the standard one and some of the 'cooling fuel' for deceleration is being ignited by the hot manifold. More fuel = fuel ignited in cylinder not hot manifold. But then vapour is more volatile than liquid. Makes sense.' On deceleration the vaccum momentarily rises in the manifold from around 8Hg to 20Hg and that causes the MU to change the fuelling. See attached. I have now had the manifolds completely reconditioned by Malcolm which eliminated the play in the spindles I had and the butterflies are as shut as I can get them on tickover with pretty much equal airflow measured on all. This has led to a dramatic improvement with the tickover smoother than ever before and virtually no misfire on overrun. An occasional dull misfire occurs when I abruptly take my foot off the accelerator and straight away lightly tap it. I suspect the latter may be caused by ignition timing as I don't have a steady timing mark with the strobe. Maybe wear in the distributor drive gear is the cause and is the next fix I will try. BTW, I cannot stall the engine by shutting the air valve, the revs. drop to around 600rpm. And I doubt that the butterflies can be completely air tight as I have always seen gaps on the sides were they are mounted on the spindles. Stan Edited June 10, 2011 by smizgals Quote Link to post Share on other sites
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