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MG MGB Technical - Carb Help

My other post was something like ‘help start my engine’. I think I got the problem narrowed down to the carbs. Thanks to all the help provided so far. Ignition is now giving a good bright white spark. Distributor needed rebuilt. Timing advance knob was missing a spring that goes next to the knob which allowed for a bit of play. Changed again the points and rotor. Timing and dwell are correct and do not float.

What the carbs seem to be doing. They are SU’s with side bowls. Car starts very easily first time WITHOUT choke, kicks right off. Power is poor, no get up and go that it did have. Does not get close to running hot. Car refused to start after the first time even if it was run only a few minutes and engine is not hot. Set the mixture at 3500 rpm using the whiskers with no problem, both pistons moving the same at any rpm. Car remains running if idle is about 1200. If I drop it down to 1000 it will run about a minute and then slowly drop off and die afterwards I pulled the tops off the carbs and there was a gas puddle around each jet.

I am assuming it is getting too much gas and wetting the plugs enough to kill the engine at idle. I have checked and rechecked the floats. Also tried setting the float lower than specs which made no difference. I have even adjusted the jets flush with the bridge which is very close to turned all the way in. No difference, car starts first time only and with a power loss. Still a gas puddle around the jet. If I look down into the jet and pull the choke all the way I can see gas just below the jet hole.

The only other thing I can think of is the jets are worn. I have compared them to a new set but it is hard to tell a difference even if I put in a needle and do not have anything else to measure it with. I would have put in the new jet but it is aluminum and I thought the brass was a better part (harder). So, am I getting close or are there other suggestions?

Again, thanks to all. Although not right yet, running is better than not running.

Randy
Randy Palsgrove

test jets by removing carb bowl tops. Blow into them and with a little pressure from your finger against jet they should stop up completely. If they are sealing I would try leaning it out in equal incriments.
J Arthurs

Hi,

Do you have the proper fuel pump? When I first got my B I had similar problems and I eventually traced the problems down to the wrong fuel pump which had been installed on the car by the previous owner. The pump was putting out fuel at too high a pressure which soon overcame the floats and flooded out the engine. I installed a low pressure pump (SU) and reset everything and it has been running fine ever since.. E
FWIW Alan
Alan

Hi,

It may be worthwhile servicing the carbs. Servicing kits are available for about GBP40, containing jets, O-rings, flot needles, seats, etc. I just just serviced the carbs on my 77 BGT - a bit of a fiddly job, but well worthwhile. The best improvement in performance, cold/hot starting and smooth tickover compared to any other "tune-up" job I've ever done!

Dave.
Dave Taylor

This thread was discussed between 06/09/2002 and 09/09/2002

MG MGB Technical index

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