Charlie D Posted August 18, 2023 Report Share Posted August 18, 2023 Hello All, Not a major problem but not sure what to make of it. I’ve done over 3000 miles since I rebuilt my engine and it has never missed a beat, always pulled away beautifully, cruised at 60+, would zoom up hills, and I was very happy. Until about 2 days ago. It started misfiring after being caught in a queue, but fairly quickly got back to normal when on the open road. Yesterday I did a 150 mile trip and the misfire got worse when in towns, but again cleared eventually, but took a little longer. The engine never overheated (Electric fan came on for a while in town, then went off and cycled it’s self in the normal manner.) I pulled the plugs today and found No2 plug much darker than the rest. (It’s the last one in the photo.) Not so obvious in the photo but very clearly a difference in real life. I also noticed a dark stain/scorch mark on the inner wing in line with the front carb inlet. Checked the cylinder compression and all were 170-173 psi. So it seems that the problem lay in No2 cylinder. If there was a carb problem it would affect No1 and No2. (Plug No1 was exactly the same colour as 3 and 4) If there was a timing issue it would affect all 4 cylinders. I’ve looked at the plug leads and inside the distributor cap and found nothing odd. I’ve moved the dark plug to cylinder No4 to see what happens, but I’ll have to replicate driving through towns and getting into queues somehow to get any idea if the plug makes a difference. The main question I’m asking is what do people make of the colours of the plugs. (What could make the dark one darker than the rest, and do the rest seem a reasonable colour anyway.) Any suggestion appreciated. Charlie. Quote Link to post Share on other sites
RogerH Posted August 18, 2023 Report Share Posted August 18, 2023 Hi Chatlie, I would go for the Carbs being affected by the heat. I assume you do not have a heat shield fitted to the barbs. Roger Quote Link to post Share on other sites
Lebro Posted August 18, 2023 Report Share Posted August 18, 2023 Those plug colours look fine to me, it's only a small difference. You need to worry when one come out black & sooty, or black & wet. Bob Quote Link to post Share on other sites
Hamish Posted August 18, 2023 Report Share Posted August 18, 2023 I would swap all the plugs out for new ones. They are consumables after all. But then I stock two set, one set hotter. Quote Link to post Share on other sites
Charlie D Posted August 18, 2023 Author Report Share Posted August 18, 2023 Roger: That makes sense in a way. While I move forwards the airflow is enough to keep the carbs cool enough. With the electric fan it is only on spasmodically, so the carbs get a blast of very hot air just after the fan turns on. Then the radiator water cools enough to switch the fan off , but it is still hot around the carbs (not helped by no heat shield above the exhaust manifold.) I could just try the manual over ride for the fan motor next time I’m stuck in a jam and see what happens. Bob: Nice to hear that they look ok. Thank you. Hamish: Yep, I know what you mean. But they should last more than 3000 miles. However, that is an option I thought about. I know there has been a lot of discussion before about what type of plug to use so I shall have a read up to see what I can find. Just need a bit better weather (and a traffic jam) to test things out. Charlie. Quote Link to post Share on other sites
monty Posted August 18, 2023 Report Share Posted August 18, 2023 Heat shield from Revington & a fresh set of genuine NGK plugs would be my starting point. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted August 18, 2023 Report Share Posted August 18, 2023 I recently bought these heat shields for my HS6 £18. delivered was a bargain https://www.ebay.co.uk/itm/MINI-HS6-1-3-4-TWIN-CARBURETTOR-HEATSHIELD/364288623605?pageci=cc40d611-0039-42a6-b4be-7417ae72d90f&redirect=mobile Quote Link to post Share on other sites
Lebro Posted August 18, 2023 Report Share Posted August 18, 2023 Photo of them installed ? Bob Quote Link to post Share on other sites
BlueTR3A-5EKT Posted August 18, 2023 Report Share Posted August 18, 2023 That’s next week in the shed…probably Quote Link to post Share on other sites
Charlie D Posted August 19, 2023 Author Report Share Posted August 19, 2023 (edited) Monty: I looked on the Revington site but to no avail. However I doubt if they would be cheaper than the ones Peter has found. Spark plugs will come from Halfords I guess. I have read before about the number of fake ones about. Peter: Excellent find. I wonder if they will fit the Strombergs though. I know the hole positions are right but not sure if they will clash with the Stromberg bodies. Plus I have a home made cable throttle which includes a bar between the two carbs to mount the cable and this might clash as well. I look forwards to seeing any photo you come up with. EDIT. Just found these for the stromberg. Totally different shape (Different float chamber, of course!) https://www.stainlessforclassics.co.uk/Stainless_for_Classics_Heatseild_ Carb _stromberg_cd175.htm Charlie. Edited August 19, 2023 by Charlie D Quote Link to post Share on other sites
BlueTR3A-5EKT Posted August 19, 2023 Report Share Posted August 19, 2023 1 hour ago, Charlie D said: Monty: I looked on the Revington site but to no avail. However I doubt if they would be cheaper than the ones Peter has found. Spark plugs will come from Halfords I guess. I have read before about the number of fake ones about. Peter: Excellent find. I wonder if they will fit the Strombergs though. I know the hole positions are right but not sure if they will clash with the Stromberg bodies. Plus I have a home made cable throttle which includes a bar between the two carbs to mount the cable and this might clash as well. I look forwards to seeing any photo you come up with. EDIT. Just found these for the stromberg. Totally different shape (Different float chamber, of course!) https://www.stainlessforclassics.co.uk/Stainless_for_Classics_Heatseild_ Carb _stromberg_cd175.htm Charlie. Charlie. Well found. I have recently gone back to a hotter plug BP5HS or Bosch Equiv. helps with the lumpy tickover when parked on the M25 for 1/2hr. Quote Link to post Share on other sites
monty Posted August 19, 2023 Report Share Posted August 19, 2023 3 hours ago, Charlie D said: Monty: I looked on the Revington site but to no avail. However I doubt if they would be cheaper than the ones Peter has found. Spark plugs will come from Halfords I guess. I have read before about the number of fake ones about. Peter: Excellent find. I wonder if they will fit the Strombergs though. I know the hole positions are right but not sure if they will clash with the Stromberg bodies. Plus I have a home made cable throttle which includes a bar between the two carbs to mount the cable and this might clash as well. I look forwards to seeing any photo you come up with. EDIT. Just found these for the stromberg. Totally different shape (Different float chamber, of course!) https://www.stainlessforclassics.co.uk/Stainless_for_Classics_Heatseild_ Carb _stromberg_cd175.htm Charlie. Sorry Charlie, I was thinking alternator heat shield from Revington! Old age blip again! Quote Link to post Share on other sites
Hamish Posted August 19, 2023 Report Share Posted August 19, 2023 Get plugs from green spark plug co https://www.gsparkplug.com Quote Link to post Share on other sites
Charlie D Posted August 19, 2023 Author Report Share Posted August 19, 2023 Thanks for the link, Hamish. £8.44 seems fine for a set of 4, but with another £4.98 postage I'll look around locally first. Charlie. Quote Link to post Share on other sites
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