SU Carb
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SU Carb
Cant seem to stop carb from running rich tried to alter turning one flat at a time but makes on difference. Can you get a kit to overall these and if so from were. Or would it be best to replace carb many thanks for any help Tom
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svenedin
- Minor Legend
- Posts: 3106
- Joined: Fri Aug 29, 2014 9:27 am
- Location: Surrey
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Re: SU Carb
I am assuming you have an SU HS2 carburettor.
Are you turning the mixture adjusting nut in the right direction? The mixture nut (the lower of the two nuts; the upper nut is the jet centring nut) should be screwed upwards to weaken the mixture. That's anticlockwise looking from above the carb.
It is possible that the jet is so worn that adjusting the mixture nut is having little effect. Other things can cause a rich mixture such as restriction of air (blocked/dirty air filter) or a float chamber with a fuel level that is much too high.
Before embarking on a rebuild check the jet is centred by removing the air filter and housing and lifting up the carburettor piston with your finger and letting it go. It should fall back with a definite metallic clunk. If it does not you will have to investigate why which may include re-centring the jet.
Rebuild kits are widely available either from SU (Burlen fuel systems) themselves or the usual suppliers. A carburettor rebuild takes time and patience. It is a precision instrument and should be treated as such. One thing that is beyond some home mechanics like me is replacement of the throttle disk bushes if they are worn. That is a skilled thing to do. Worn throttle disc bushes cause air leaks that weaken the mixture though and that is not your problem! If you do not feel up to rebuilding the carb yourself then you can exchange it for a reconditioned one from ESM or other suppliers. SU sell a workshop manual for carburettors and fuel pumps that is very useful. Be aware that various carburettor nuts are BA sizes so a BA socket set is essential. Also to remove the float needle valve seat requires a special thin walled tiny box spanner (a normal socket will get jammed). Shop around for the best deal on parts and/or a rebuilt carb.
I like Southern Carburettors for parts: https://www.southerncarbs.co.uk/page_1822386.html
Good luck!
Stephen
Are you turning the mixture adjusting nut in the right direction? The mixture nut (the lower of the two nuts; the upper nut is the jet centring nut) should be screwed upwards to weaken the mixture. That's anticlockwise looking from above the carb.
It is possible that the jet is so worn that adjusting the mixture nut is having little effect. Other things can cause a rich mixture such as restriction of air (blocked/dirty air filter) or a float chamber with a fuel level that is much too high.
Before embarking on a rebuild check the jet is centred by removing the air filter and housing and lifting up the carburettor piston with your finger and letting it go. It should fall back with a definite metallic clunk. If it does not you will have to investigate why which may include re-centring the jet.
Rebuild kits are widely available either from SU (Burlen fuel systems) themselves or the usual suppliers. A carburettor rebuild takes time and patience. It is a precision instrument and should be treated as such. One thing that is beyond some home mechanics like me is replacement of the throttle disk bushes if they are worn. That is a skilled thing to do. Worn throttle disc bushes cause air leaks that weaken the mixture though and that is not your problem! If you do not feel up to rebuilding the carb yourself then you can exchange it for a reconditioned one from ESM or other suppliers. SU sell a workshop manual for carburettors and fuel pumps that is very useful. Be aware that various carburettor nuts are BA sizes so a BA socket set is essential. Also to remove the float needle valve seat requires a special thin walled tiny box spanner (a normal socket will get jammed). Shop around for the best deal on parts and/or a rebuilt carb.
I like Southern Carburettors for parts: https://www.southerncarbs.co.uk/page_1822386.html
Good luck!
Stephen
1969 1098cc Convertible “Xavier” which I have owned since 1989.
Stephen
Stephen