dcz1643 Posted October 16, 2018 Share Posted October 16, 2018 Hi All.... I intend to service/re-build my twin SU's over the winter, on my 1974 1300 Spit, as they sometimes stick. I have been considering adding a stainless steel heat shield whilst I have the carbs off. My question is, does a heat shield bring any mechanical benefit to the car, or is it just cosmetic. Cheers...Derek Quote Link to comment Share on other sites More sharing options...
Steve AKA vitessesteve Posted October 16, 2018 Share Posted October 16, 2018 Does your car suffer when hot - carb heat shields can reduce problems (vapour lock) caused by the hot exhaust under the carbs. Also the shields can add a bit of bling if that floats your boat. Quote Link to comment Share on other sites More sharing options...
glang Posted October 16, 2018 Share Posted October 16, 2018 I couldnt reply to the previous thread by Derek for some reason so started a second one to answer his question: The idea of these is not cosmetic but to keep the carbs cooler by preventing radiant heat, usually from the exhaust manifold, from reaching them. If a carb becomes too warm it can suffer from fuel vaporisation which causes it to malfunction and not supply fuel correctly to the engine. This usually occurs during slow running or after stopping when theres less cooling air flow and results in poor running and/or hot starting. Quote Link to comment Share on other sites More sharing options...
dcz1643 Posted October 17, 2018 Share Posted October 17, 2018 Hi Stephen, I don't think my engine suffers when hot but I do have an issue with setting the idle speed. Sometimes when it is warmed up, the engine will idle at over 1000 revs, when it is set around the 750 mark. That is one of the reasons to completely strip and service the carbs, as well as changing the throttle cable and perhaps change the linkage bushes. The choke also sometimes gets stuck and I need to lift the bonnet to manually take it off. Therefore I will also replace the choke cable. I think I will add a heat shield, as what I am trying to achieve is a troublesome free set of carbs. I am also considering putting twin K&N filters on, I assume this will help with my objective. Thanks for your reply....Derek Quote Link to comment Share on other sites More sharing options...
RobPearce Posted October 17, 2018 Share Posted October 17, 2018 I don't think the K&Ns will help. Stick with the original air box. Inconsistent idle is most often caused by air leaks, whether that be poorly sealing gaskets or worn throttle shafts, but the sticking choke could also point to other things not returning smoothly. Quote Link to comment Share on other sites More sharing options...
PeteStupps Posted October 18, 2018 Share Posted October 18, 2018 I've got some similar issues with my HS2 SU's coincidentally, which are a reconditioned pair put on by a previous owner. It has taken much swearing to figure out the source of the problems. Not assuming yours is exactly the same as mine but are you sure the choke sticking is related to the cable? On mine it's the jets, specifically the rear one. I've adjusted it many times but it's still sticky in the sleeve/bearing when taking choke off. Maybe the extra drag of the cable contributes, I should re-investigate. On the tick-over, my front carb throttle butterfly doesn't fully close unless you give the throttle arm a slight push (maybe a stronger throttle spring would help). Result being that the tickover will never settle below 1000rpm without opening the bonnet and intervening, and if I adjust the rear carb to get them in balance it ticks over even faster. As far as I can tell the butterfly just doesn't fit properly. Whoever did the reconditioning didn't do a very good job (except for polishing the dashpots). In your case, have you given the throttle linkage a wiggle when it's warmed up, to see if there's something binding? My experience with a heat-shield is very positive though. Used to suffer evaporation (stuttering, hesitation on acceleration) in traffic in warm weather, and the heat-shield has completely eradicated that. Living in London, all my journeys start or end (or both) with traffic jams so it has made the car much more usable. Not much good having a convertible that doesn't behave on warm days! Agree with Rob that K&N filters probably won't help in your objective though. Have you got the cold-air feed to the standard filter box? Think that's meant to be best unless you're tuning for high performance. Quote Link to comment Share on other sites More sharing options...
dcz1643 Posted October 18, 2018 Share Posted October 18, 2018 Hi Peter, thanks for posting.... The choke is physically sticking but as you say, my assumption that it is the cable could be incorrect, it could be the actual carbs sticking. I will look into this when I take the carbs off. Regarding the idle speed, I can sometimes get it to slow down by pulling down on the accelerator cable but it doesn't always work but again you have given me some things to look into. I am doing the 2019 France RBRR next year, so I will fit a heat-shield, I think it would be prudent. When the weather turns (still enjoying blasting down the country lanes with the roof down), I will strip everything down, so your comments are very helpful . Cheers....Derek Quote Link to comment Share on other sites More sharing options...
Bitumen Boy Posted October 18, 2018 Share Posted October 18, 2018 Quoted from PeteStupps- Not assuming yours is exactly the same as mine but are you sure the choke sticking is related to the cable? On mine it's the jets, specifically the rear one. I've adjusted it many times but it's still sticky in the sleeve/bearing when taking choke off. Maybe the extra drag of the cable contributes, I should re-investigate. Try removing the sticky jet and giving it a quick polish with Brasso or similar, worked for me before now. Quote Link to comment Share on other sites More sharing options...
RobPearce Posted October 18, 2018 Share Posted October 18, 2018 Quoted from PeteStupps- On the tick-over, my front carb throttle butterfly doesn't fully close unless you give the throttle arm a slight push (maybe a stronger throttle spring would help). I had that on my Spitfire (HS4s but the same principle). On closer inspection it turned out the throttle return spring on the front carb was fitted wrongly - the static end resting against the flange instead of the carb body, so about half a turn too little tension. Quote Link to comment Share on other sites More sharing options...
Clive Posted October 19, 2018 Share Posted October 19, 2018 I had that on my Toledo. Turned out to be wear on a spindle causing it to snag. New spindles and job done. Just an idea of course... Quote Link to comment Share on other sites More sharing options...
Guppy916 Posted October 20, 2018 Share Posted October 20, 2018 I purchased some for my GT6 from e-bay seller "buyright777" for my 40 DCOE's this link is for SU carbs https://www.ebay.co.uk/itm/TRIUMPH-Parts-Triumph-TR6-TR5-Twin-SU-HS6-Carburettor-Heat-Shields/302917176791 Quote Link to comment Share on other sites More sharing options...
daver clasper Posted October 20, 2018 Share Posted October 20, 2018 Some folk just shape thick foil (barbi etc) around the float bowls, when hot weather. Dave Quote Link to comment Share on other sites More sharing options...
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