25-01-2019, 12:25 AM
(This post was last modified: 25-01-2019, 01:19 AM by Jeff Taylor.)
Garry,
You'll need to give us more information regarding the model of SU carb you have - there should be a body number on the side of the main body casting - a photo of your carb would also be helpful. It does sound as if yours is probably a pre-war carb.
Generally most if not all pre-war side-draught SU's had neither a spring nor a damper - the dashpot piston being weighted should fall on its own accord without the need of any spring assistance. Dampers were a post-war development. It's possible you may have an early 1930's SU OM - 1" carb - body number 617 - these were originally fitted to early MG's - no spring and no damper. The SU H1 - 1.1/8" carb - body number 3457/1 fitted to 1948 to 1953 Morris Series MM Minors (a popular carb fitted to a number of Sevens) did have a dashpot damper but definitely no spring.
Have you tried fitting a brand new needle valve in the float chamber. Also check that the float fork is correctly adjusted using a 3/8" diameter bar or dowel - illustration to follow. I'd also carefully check the brass float for any pin prick holes around the soldered joints allowing petrol to get inside and weigh it down. Check that the 0.090" jet is correctly centred and that the dashpot piston rises and falls back cleanly without any restriction.
Is your electric fuel pump also an SU ? if it is, then new diaphragms are available from Burlen that are suitable for modern fuels.
If you require any spare parts then Burlen stock almost everything you might need to refurbish your carb - link below.
http://sucarb.co.uk/?SID=qpkjp3c2kb5u2f0...__store=su
You'll need to give us more information regarding the model of SU carb you have - there should be a body number on the side of the main body casting - a photo of your carb would also be helpful. It does sound as if yours is probably a pre-war carb.
Generally most if not all pre-war side-draught SU's had neither a spring nor a damper - the dashpot piston being weighted should fall on its own accord without the need of any spring assistance. Dampers were a post-war development. It's possible you may have an early 1930's SU OM - 1" carb - body number 617 - these were originally fitted to early MG's - no spring and no damper. The SU H1 - 1.1/8" carb - body number 3457/1 fitted to 1948 to 1953 Morris Series MM Minors (a popular carb fitted to a number of Sevens) did have a dashpot damper but definitely no spring.
Have you tried fitting a brand new needle valve in the float chamber. Also check that the float fork is correctly adjusted using a 3/8" diameter bar or dowel - illustration to follow. I'd also carefully check the brass float for any pin prick holes around the soldered joints allowing petrol to get inside and weigh it down. Check that the 0.090" jet is correctly centred and that the dashpot piston rises and falls back cleanly without any restriction.
Is your electric fuel pump also an SU ? if it is, then new diaphragms are available from Burlen that are suitable for modern fuels.
If you require any spare parts then Burlen stock almost everything you might need to refurbish your carb - link below.
http://sucarb.co.uk/?SID=qpkjp3c2kb5u2f0...__store=su