There are many threads on different forums about running a bike/car on Castrol R - and adding it to petrol for the smell
many (inc me) like the smell - reminds me of speedway and race meetings with my dad in the late 60's and early 70's . Also many do not....
Some maintain it gums up the piston rings if mixed with petrol as a "perfume" additive - others say not and have never experiences any issues...
Here is a response posrted on Piston Heads from either a UK oil supplier for classic cars and bikes - might have been Opie or a Castrol main distributor (I can't remember but just saved the text) to an enquiry about the same thing.................
"I can confirm that you can still purchase Castrol R as a SAE 40 grade oil. Castrol R 40 can be obtained from Castrol Classic Oils (Tel: 01954 231668 or see the link on the Castrol.com/uk website) or one of their distributors.
We don’t really recommend it for use in modern machinery because there are more suitable modern oils available such as Castrol Power 1 Racing 10W-40 and Castrol Power 1 GPS 10W-40. The oil change guidelines for your machine will be calculated based on the use of a modern oil such as these and it is difficult for us to give accurate advice on what frequency of oil change would be needed if you were running on Castrol R40, but it could be as low as every 1,000 miles.
Castrol R 40 is a very good lubricant under certain circumstances, however it is relatively unstable and will therefore tend to promote the build up of deposits in your engine. It may not work perfectly with your wet clutch either.
The instability of Castrol R means it is also not recommended for long term storage, so if you were going to store your bike for 6 months, we would suggest you consider filling with new Castrol R at the start of the storage period and draining and replacing with new oil at the end, before using the bike again. If storing for longer than 6 months, it may be worth switching back to a modern mineral, part-synthetic or full synthetic.
We are often asked about the best way to obtain the Castrol R odour and from our discussions we are aware that many people add a small amount to their fuel. Just how much seems to be an inexact science, but generally the less you can get away with the better. You might like to start with 1000:1 fuel:R ratio (20ml of R in a 20 litre fuel tank) and see how that works, adding more oil if there is insufficient effect. I would suggest if you get as far as 100:1 (200ml of oil in a 20 litre fuel tank) and still aren’t getting the effect you want, you might want to re-consider the benefits versus the downsides!"
