Green’s Dictionary of Slang

raker n.²

1. a very fast pace.

1876		Coursing Calendar 38: Poacher, going a raker from Cannobie lea, never let the latter next the hare in a well-run course of good length [OED].
1895		Daily News 8 July 8/6: The pace home was a raker, the three boats throwing up great sheets of white water [OED].

2. a heavy bet.

1877		Leader (Melbourne) 5 May 12/4: Sir John lost a lump on him, but landed a ‘raker’ over the hurdle race.
1884		H. Smart Post to Finish I 9: If Bill Greyson takes the Leger it will be with Caterham. I am standing him a raker, and I mean standing him out.
1885		Queenslander 10 Jan. 49/4: If I won a good stake over Caterham for the Guineas, I lost a raker over him for the Derby .
1890		Sporting Times 12 Apr. 1/4: He (the case) goes on a raker on Sweetbriar.
1900		Sth Bourke Jrnl (Richmond, Vic.) 21 Nov. 3/3: Despite the defeat of Lancaster in the Cup, there is no doubt about his merit. Foulsham stood to win a raker over him.

In phrases

go a raker (v.) (Aus.)

1. to place a heavy bet.

1873		Sl. Dict. 266: Raker, to go a is in racing parlance, to put more money than usual on a certain horse. ‘Going a raker’ often leads to ‘coming a cropper’.
1878		Queenslander (Brisbane) 13 Apr. 46/2: When you have all the chips on and to win, you / Have gone a raker, guess the frightful scare / When, full of go, your champion strains a sinew.
1882		Sydney Sl. Dict. (2 edn) 7: Raker (To go a) - In racing parlance, to put more money than usual on a horse. ‘Going a raker’ often leads to ‘coming a cropper’.
1890		Dead Bird (Sydney) 27 Sept. 6/2: He was determined to go a raker this time, and made a good haul.
1898		Hamilton Spectator (Vic.) 13 Aug. 1/2: His owner had backed him heavily, and, in stable phrase, had gone a ‘regular raker’.
1904		Referee (Sydney) 1 Nov. 8/7: The horse was much fancied, and the jockey had gone a ‘raker’ on him.
1914		Dly Herald (Adelaide) 10 Jan. 4/8: One night he had been winning heavily and the youngster, with his usual rashness, had gone a raker and lost.

2. to fall heavily.

1941		Baker Popular Dict. Aus. Sl.
1945		Baker Aus. Lang.