Agree with 5T - those intake rubbers, carb to cylinder head, don't look too happy. The trick is to spray carb cleaner directly onto the cracked area while the bike is running and see if the revs go up. I think I got that right but if not somebody will correct.
An air leak in the intakes will cause an erratic idle but will not necessarily show up in the plug condition because the fueling might be much better when you open the throttle to ride round the block
If you need to replace cracked intake rubbers then tank, air filter boxes and carbs will need to come off. Access varies with model and carb type but it is always very tight in there. I loosen and remove one of the intake rubbers - the right one - to get a bit more space. Other people remove the nut on the cam chain adjuster to make more space. I also wrap a piece of rag around the frame behind the carbs, then they can be pulled off and wiggled free.
When fitting new intake rubbers, you also need to check the gasket between the intake and the head and make sure this area is clean. Reinstall with a smear of grease or some non-setting gasket goo such as Hylomar.
I'm slightly confused by all the hoses in your photos - bear of small brain! The one with your thumb in the first photo does not appear to be the petrol feed from the petcock. Cylinder head breather? Looks as if your bike has a vacuum operated fuel tap - the hose below that from the inlet rubber to the fuel tap. I can't see anything to worry about rubbing on the cylinder head.
An air leak in the intakes will cause an erratic idle but will not necessarily show up in the plug condition because the fueling might be much better when you open the throttle to ride round the block
If you need to replace cracked intake rubbers then tank, air filter boxes and carbs will need to come off. Access varies with model and carb type but it is always very tight in there. I loosen and remove one of the intake rubbers - the right one - to get a bit more space. Other people remove the nut on the cam chain adjuster to make more space. I also wrap a piece of rag around the frame behind the carbs, then they can be pulled off and wiggled free.
When fitting new intake rubbers, you also need to check the gasket between the intake and the head and make sure this area is clean. Reinstall with a smear of grease or some non-setting gasket goo such as Hylomar.
I'm slightly confused by all the hoses in your photos - bear of small brain! The one with your thumb in the first photo does not appear to be the petrol feed from the petcock. Cylinder head breather? Looks as if your bike has a vacuum operated fuel tap - the hose below that from the inlet rubber to the fuel tap. I can't see anything to worry about rubbing on the cylinder head.