I wonder if a simple water/methanol injection into the inlet tract would give enough protection to the valves to stop the build up?
Kits are available but expensive and aimed at forced induction. We need a competent expert to evaluate possible benefits, and come up with a simple kit for the GDi.
I won't hold my breath. Mine is just at 10,000 miles and I'm tempted now to take the manifold off over winter to see what 10,000 miles looks like.
The cost effective alternative would be an LPG valve saver kit Dave, these systems are inexpensive and highly effective.
https://lpgshop.co.uk/flash-lube-electronic-valve-saver-kit/The above version uses an ECU that takes a MaP reference from the inlet manifold to meter the valve saver lube, however, in my experience the following far simpler and cheaper vacuum based JML kit that only costs £35.00, works just as well.
https://lpgshop.co.uk/jlm-valve-saver-kit/I would add the four cyliner distribution manifold to your basket too, it's only £20 and essential to ensure an equal quantity of fluid reaches the back of all four valves evenly.
https://lpgshop.co.uk/lubricant-distributor-splitter-4cyl/While these simple systems are designed to cool and lubricate your valve seats when running LPG which is a dry fuel, the lube used in these systems also has excellent detergent properties, this will remove any existing carbon and blowby deposits on the back of your valves while keeping it bay in future.
https://lpgshop.co.uk/flash-lube-valve-saver-fluid-0-5liter/A 500ml bottle of flashlube only costs £15.00 and will last at least ten fills, so roughly 4,000 miles in a GDI Plus 4 which works out at next to nothing per mile, you can also mix the lube 50/50 with methanol, this gives even better blowby cleaning properties and the added benefit of cooling the incoming charge with a small increase in octane too.
https://www.ebay.co.uk/itm/354307108272?hash=item527e596db0:g:l14AAOSwCdNkIupo&amdata=enc%3AAQAIAAAA4OnfuorIBGw5Sh7iuFQG4nO0GomWMSLVsLLPMOZD444JSKLqeo5s5WWoH2WBl5%2FZWOGEQUTJcuJYYZcLH3utSGVYhHQd8Qdu996HvGp%2BTFWxXRO9zlfcxof1XSedNj4%2BhB%2B%2BWcjyRD9pOAc3FldSeMX2Cbpi3FqPnHGO6j7UeGRasK9FnDKmEiZ6GbhFZPHDyd5MASJ%2BimnZRn5MfzYIWiX4jQouqglv%2B3%2FnKuRYiknAGZvKJvfpGf2oY6vQpFXcGe9NLCUL3c2iYWmZwGRrpZKNt8AoyU%2BUTk2GlOFuR08M%7Ctkp%3ABk9SR-KX3vHoYg
You can buy 500ml of methanol from eBay for just £8.00, so for less than £25 you've bought yourself 8,000 miles of valve cleaning solution, including the kit itself & distribution manifold you’ve solved the problem for years to come and for just £80.00

![[Linked Image]](https://i.ibb.co/ZLjTX9r/jlm-lpg-cng-valve-saver-protection-kit-37486.jpg)
![[Linked Image]](https://i.ibb.co/98djBbC/JLM-Valve-Saver-Spliter-Top-12875.jpg)