Nice set; I'll only make a few changes here and there.
Here's the set I use:
EVs: 116 Atk / 156 Def / 236 Sp. Def
- Bulk Up
- Knock Off
- Mach Punch
- Drain Punch
The EVs should be adjusted to 116 Atk / 156 Def / 236 Sp. Def. This allows it to take a Hydro Pump from +2 Omanyte. The chance of certain threats, such as Abra's Psychic and Fletchling's Acrobactics, OHKOing Timburr, is unlikely with this spread. In addition, it allows it to retaliate with a powerful Knock Off. The rest of the EVs are invested in Atk / Def evenly because it gives Timburr good Defense and Attack after setting up Bulk Up.
Poison Jab is nice for 2HKOing Spritzee, while surviving the STAB Moonblast. Timburr really prefers the STAB priority to pick off weaker targets (ex: Sashed Abra almost got OHKOed by Knock Off, but Mach Punch can finish it off), so I would replace Poison Jab with Mach Punch.
Bulk Up is a great set-up move, which Timburr can use when the opposing Pokemon switches out.
Knock Off deals with Psychic-types, such as Abra, and can dent Ghost-types, such as Gastly.
Mach Punch is great STAB and priority. It can be used to finish off weakened targets.
Drain Punch is STAB and it Timburr's only form of recovery.
196+ Atk Fletchling Acrobatics (110 BP) vs. 0 HP / 156 Def Eviolite Timburr: 18-24 (75 - 100%) -- 6.3% chance to OHKO after Stealth Rock
240 SpA Abra Psychic vs. 0 HP / 236+ SpD Eviolite Timburr: 18-24 (75 - 100%) -- 6.3% chance to OHKO after Stealth Rock
116 Atk Timburr Knock Off vs. 0 HP / 0 Def Abra: 20-24 (105.2 - 126.3%) -- guaranteed OHKO
(even if Abra has Sash, Timburr can finish it off with Mach Punch)
200 SpA Life Orb Gastly Sludge Bomb vs. 0 HP / 236+ SpD Eviolite Timburr: 12-16 (50 - 66.6%) -- guaranteed 2HKO after Stealth Rock
116 Atk Timburr Knock Off (97.5 BP) vs. 0 HP / 0 Def Gastly: 24-30 (126.3 - 157.8%) -- guaranteed OHKO
Note: As threatening as Timburr sounds like, it can get walled by Fairy-types and 2HKOed by Flying-types and Psychic-types. For this reason, Skrelp makes a good partner because it can deal with Fairy-types. Pawniard can deal with Flying-types / Psychic-types.