"Popping" sound in the exhaust upon deceleration

Having just converted the aging Solex to twin SU's in my TA21 I am in the process of getting the settings right. The car runs beautifully but there is a popping sound in the exhaust when coasting downhills. I presume it is related to mixture and to that end am wondering if it may be running a little lean.  I would appreciate members thoughts.  Richard Melbourne Posted by RichardWallach 07/01/2017 00:20:51

Had the same on the Speed 25. Popping usually means fuel in the exhaust system, and in my case leaning out the  3 SUs resolved.  Good luck! Posted by johnlayzell 07/01/2017 16:04:13

Don't be too hasty to alter things. It should pop a bit on overrun on SU's I think. I have the same issue on my TC having had it correctly tuned on a rolling road by somebody who actually knows what they are doing. I queried it at the time because it didn't happen before it was tuned.  It's something to do with the vacuum created when the carb butterflies are closed as I recall. Posted by Angus D'Arcy-Drake 09/01/2017 09:48:57

Another possibility is that you have a manifold leak - unburnt fuel in the exhaust combined with fresh oxygen via a leak (and the heat of the exhaust pipe) can cause this effect.  Dave Posted by DaveT 18/01/2017 09:10:15

The "popping" issue has been sorted. It was Dave's suggestion that prompted me to better sort out the exhaust leak where the pipes join the manifold. This having been done the "popping" has gone away.  Thanks for all the suggestions.   Richard Medlbourne Posted by RichardWallach 19/01/2017 21:51:57

Richard - can you expound on the "better sort out the exhaust leak where the pipes join the manifold" ?  New gaskets?  Just tighten all the nuts a little? Both?  Other?  After sitting for four months, the Speed 25 was similarly popping this AM, which it had not done when parked!  Thanks! Posted by johnlayzell 12/03/2017 15:10:44

John,  I have had considerable trouble trying to get a good seal between the exhaust pipes and exhaust manifold. The two surfaces are fastened by three studs with a joint washer in between. The surfaces did not mate well and a local gasket for a modern that fitted quite well would continue to blow out. The result was much unpleasant noise and exhaust popping on overrun. I had tried gasket cements etc with the same unsuccessful outcome. The physical tell tale being the continued blackened area in one particular spot between the two surfaces.    The fact that I could buy a local gasket meant that I didn't get one from RT. I checked to see if RT sold them and was surprised to see a picture of one on their website. Theirs was a thicker gasket made of copper. I subsequently purchased one.  It compressed well and effectively sealed the joint. The end result is no noise and a total absence of popping. I must add that the quality of the joint washer is excellent.  I hope this helps.  Richard Melbourne Posted by RichardWallach 12/03/2017 21:18:13

Since my last post I have replaced the single exhaust manifold with the later TC pair first sealing off the hotspot bolt holes on each manifold. This is a most worthwhile upgrade. No longer do I have gasket issues. That said the big plus is the better exhaust extraction. There is a noticeable increase in acceleration. Unfortunately part of the conversion cost was putting the car onto a tray truck in order to get it to the exhaust specialist as a new pair of front pipes is necessary. Posted by RichardWallach 23/10/2017 06:16:04