23/03/2025
Hi all.
We get an awful lot of questions regarding overheating and irregular idling when it comes to engines fitted with dellorto sha1412 carbs/Morini S5/S6 engines and others.
Yes, it's an issue that needs to be sorted quickly before its too late causing damage to your piston and cylinder and beyond. In most cases the culprit is an air leak/false air drawing into the inlet.
Not the easiest to explain without physically showing a customer but please check out the images.
There is an intergrated clamp on these carbs with a machined gap which needs to be sealed from the inside.
This gap needs to be sealed and tightened onto inlet/reed inlet pipe and air tight, It is important that the correct sleeve and seal is used.
Some sleeves are shorter and require an L shape seal, some sleeves reach into the carb and form a seal with an O ring seal into the carb inlet body (inside).
Some sha gasket/seal sets come with them and some do not, so it's important to pick the right one and recognise what sleeve you have.
Images 1 and 2 you can see the machined clamping gap from the outside.
Image 3, an example of the sleeve mentioned.
Images 4 and 5 L type seal for shorter sleeves.
Images 7 and 8 are two examples of the types of layouts used.
*Final image, you can see the machined clamping gap on carb inlet side. Updated with a clear picture *
Air leaks can be an issue with oils seals and also other gaskets but I hope this helps to diagnose possible issues with used bikes and gives you a place to check out first!
Always make sure your carb is clean, correct spark plug and the correct oil to fuel mixture is used in manufacturer's instructions.
Col O.R.B
