MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Reluvtant starter

Hi,

A friend's mg now seems to start very reluctantly, it was fine until a couple of weeks ago. It is now easier to start with the choke hardly out. It is then very hesitant and when the throttle is opened the engine revs drop and it wants to die.

Looked at linkages and balance and they all seem fine. Don't have carb cleaner to spray to check for leaks at spindles. Any other pointers/ideas before I try for a full retune?

Ta,

Iwan
Iwan Jones

Engine that dies when the throttle is opened is a symptom of fuel starvation. Is the pump OK?
Mike Howlett

Thanks Mike,

However, we later found some 'easy start' type spray at his garage. Sprayed this at the throttle body at the linkage spindle entry points and ..... yep, the revs increased.

So I think he has to have some bushings put into the throttle body and new linkages.

Any advice on where to get the bushings and linkages?

Thanks,

Iwan
Iwan Jones

Iwan, you'll get all the SU carb parts you'll ever need from here. http://sucarb.co.uk/

Also there is some really good technical information on the website for both HS and HIF carbs and how to dismantle and reassemble them

Andy
Andy Robinson

Something that was fine until a couple of weeks ago then suddenly started doing this doesn't sound like worn bushes and spindles to me.

Yes, the idle revs changing when you spray something at the bushes does indicate there is wear there, so may need attention, but may not be the only problem.

Starting with very little choke now sounds more like an over-rich mixture, which can also cause stumbling as you open the throttle and the mixture gets even richer from the effects of the carb dampers.

Assuming the float chambers are full to start with then any stumbling as you open the throttle cannot be due to the pump, that can be stopped for a couple of minutes or more before it starts to affect the engine.
paulh4

Stuck/sticking dashpot piston -- ????
OR
If you think it's fuel related it will probably be electrical - Checked the point gap recently ,they may well be closed down and causing a problem

willy
William Revit

Thanks all,

Yes, as Paul has outlined, my thinking was there must also be something else as the leak at the spindles would not have become bad 'suddenly'.

Think I'll have to go through things methodically. Ta Will, a sticking piston may well be on the cards as my mate mentioned it was sticking before.

Ta
Iwan Jones

Also check for vacuum leaks. Had similar hard start problems and idle issues only to find vacuum leaks around the intake / exhaust manifold and carburetor to intake manifold.

Cheers
Gary
79 MGB
gary hansen

Worn spindles wouldn't cause a problem when you open the throttles the air that can by-pass the spindles is very small compared to a wide open throttle. As Paul said probably running rich which could be just a flooding float chamber, or sticking piston or indeed a sticking choke, you didn't say what year B and which Su's. Check the overflows and make sure the pistons are free to rise and fall.
Also as Willy posted out many Su problems are Joseph Lucas in origin.
Allan Reeling

Hi,

Well done Gary, you win the prize. It was leaks at the manifold gaskets; not on tight enough; or, they had compressed further after initial tightening. Wo knows?

So, when I sprayed 'starting spray' at the spindles it would raise the idle because the carb/gasket/manifold interface is just behind spindles.

Ta, once again.

Iwan
Iwan Jones

This thread was discussed between 11/07/2016 and 17/07/2016

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now