I have a honda gv100 lawn mower and there is no petrol going to the engine

could be one of many things, what have you checked so far??

drain oil when warm then add oil to it still safe on filler dipstick oil reaches the that level it is full

if you are talking just the cord it should be okay. A vid on replacing a starter cord...

https://www.youtube.com/watch?v=iczCZaRiR0Q

The manual is on this link: http://engines.honda.com/parts-and-support/owners-manuals/GCV160 The manual depends on the serial number. It does not appear to have adjustable choke.

Bad plug. Bad gas. Dirty carb. Dirty air cleaner.

yes....clean your carb , it is gunked up from setting

problem is fuel starvation or a 'lean condition'

carburetor main jet, bowl, and pilot air jet need to be cleaned

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

SOUNDS LIKE YOU HAVE BAD GAS YOU MAY TRY CHANGING YOUR GAS

The 'DIPLOMAT' series of WEBBs is bad news, its NOT a WEBB! Webb were swallowed by qualcast-atco-suffolk, who dunped Webbs tooling, & dressed up punches & commodores in thin disguises, dumped the briggs & stratten engine for their own alloy job, & charged a rip off premium for the Webb decals!
The qualcast suffolk alloy engine suffers from a WIPAC electronic ignition unit. As it gets old, it fails, sometimes completely, sometimes as it warms up. Once cool, it works for a while again.
Not too hard to replace, but hard on the wallet, £69 genuine, £40 fake! On the whole its not too bad an engine if cared for & oil changed often. better to look on ebay for a cheap used HONDA engine & transplant! R-E-L-I-A-B-L-E !............I did! ( £35 honda gc series, 5,5hp! )

Hey Graham:

Here is an owner's manual for your lawnmower.

sysdoc.doors.ch/HONDA/31VA5030.PDF

Enjoy!

Steve