Robin Posted June 14, 2023 Report Share Posted June 14, 2023 The idle speed on my mk2 Vitesse has stared to drop for no obvious reason. It idles at around 900rpm for about 5 secs and then drops to around 500rpm for a few seconds and then pick up again and repeats but never stalls . Only started happening yesterday - could it be the hot weather or is it a fuel issue? Two videos attached showing what happens (I'm not touching the accelerator) IMG_8983.MOV IMG_8981.MOV Link to comment Share on other sites More sharing options...
johny Posted June 14, 2023 Report Share Posted June 14, 2023 First easy check is of the diaphragms. Whip the covers off and get them out for an inspection by stretching them slightly to look for splits or holes. Theres no need to remove from the pistons but note the little lugs they have that must engage correctly with carb body when reinstalling them... Link to comment Share on other sites More sharing options...
Iain T Posted June 14, 2023 Report Share Posted June 14, 2023 (edited) Before you take the cap off the carbs remove the piston damper and stick your finger in the carb and lift the piston. Then let it drop. It should drop with a nice metallic clonk. If it doesn't the jet needs centralising. Also if you take the cap off as Johny suggests to check the diaphragms when you reinstall ALWAYS do the above procedure to make sure the needle is centered. If its not you can get hunting or uneven tick over..... I know! Sometimes when retightening the four cap screws a small nudge on the cap is all it takes to get a nice clonk! The clearance between the jet and needle is very small so it's easy for the needle not to sit down correctly which can hold the piston up and let air in at a lower velocity hence less fuel. Iain Edited June 14, 2023 by Iain T 1 Link to comment Share on other sites More sharing options...
Robin Posted June 14, 2023 Author Report Share Posted June 14, 2023 OK - thanks for the tips Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 15, 2023 Report Share Posted June 15, 2023 the floating could be down to pump supply as the carbs float level drops and the dreaded rubber slivers are at work do make sure the air cleaner gasket is not obstructing any front face air holes Pete Link to comment Share on other sites More sharing options...
Robin Posted June 16, 2023 Author Report Share Posted June 16, 2023 Quick update - tracked the problem down to the breather valve assembly. There were two holes in the rubber diaphragm - now replaced and idle back to normal. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 16, 2023 Report Share Posted June 16, 2023 good one Robin Pete Link to comment Share on other sites More sharing options...
Iain T Posted June 16, 2023 Report Share Posted June 16, 2023 Well done Sherlock! Iain Link to comment Share on other sites More sharing options...
daverclasper Posted June 18, 2023 Report Share Posted June 18, 2023 On 16/06/2023 at 14:45, Robin said: Quick update - tracked the problem down to the breather valve assembly. There were two holes in the rubber diaphragm - now replaced and idle back to normal. Yes. Had hunting, and tried various ideas off forum. Was my breather diaphragm Link to comment Share on other sites More sharing options...
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