Compression test?

[Tony Press]

Hi Chris, 

Hope you dont mind im having some trouble getting a 1928 austin 750 engine to start. 

What would be the reading for a cold compression test ? 

Im showing 50 50 48 50 1 through 4. Im failing to get more than a puff puff and some exhaust gasses so somethings happening but i'm failing to get her running.

Ive checked spark ( good converted to 12 v) so strong spark all plugs.

I have a brass updraft carb ( zenith 22 ) and i'm getting suck at the air inlet. No idea if the carb is good or how the mix is controlled but theres some fume smell in the chambers but not a lot. i worked my way from the chamber through manifolds and sealed up all leaks.

Ive adjusted timing right round and appears quite retarded is best setting currently but again nothing more than puffs smoke and as i cant run her 10 minutes to check hot compression wondered what would be expected, seems very very low to myself.

The standard Austin 7 Compression Ratios are-

1923-1933 4.8 (or 4.9) to 1

1933-1936 5.2 ? to 1

1936- 1939 6.0 (or 6.2?) to 1

Compression Pressures are between 17 and 20 times the Compression Ratio in a good engine giving :

4.8 to 1 = 80 to 96 psi

5.2 to 1 = 88 to 104 psi

6.0 to 1 = 102 to 120 psi   

Hand cranking with a 'dry' engine and throttle open you should get at least 80 psi from a standard early head (single bolt water manifold) and 100 psi from the 1936 head (two stud water manifold) if rings and valves are good.

All cylinders should be within 5 psi.