MG Car Repair: 1975 MGB Hard Starting Problems, rich mixture, float chamber

Question
QUESTION: I have a 1975 MGB with SU carburetors.  The car just will not start when it has been setting for a few days.  It will crank with no sign of ignition.  If I pump the gas peddle and come back in about 2-3 minutes, it will try to start but will be very ruff like it is only running on 2 cylindars.  If it starts, it must warm up before I have any power.  After it is warm, it runs great.  It will start all day long with no problems on the first crank.

Help?

ANSWER: Hi Richard,
First is this a Euro car or a US car that has been converted back to SUs?
If it runs good warm but is hard to start cold, you need to check to see that the choke is working. (the choke is not a butterfly like domestic cars had) when you pull the choke, your are lowering the jets in both carbs to get a rich mixture. You also need to check to see that you have oil in the top pots as that is what takes the place of an accelerator pump. Pumping the gas pedal does absolutely nothing as there is no accelerator pump on the SUs.
Howard

---------- FOLLOW-UP ----------

QUESTION: The car is US and has a 1974 SU carb and exhaust.  We have a manual choke that was added.  Oil is fine in the pots.  I will stop pumping since you have enlightened me.  The past owner said he always started it with starting fluid if it sat for a while.  How do I check to see if the carb is working.  It seems like there is no fuel in the carb.  The fuel pump sounds good but is there a way to check for gas in the carb at cold start?

Thanks.

Answer
Hi Richard,
It depends on which SU carbs you have. If the float chamber is mounted on the side of the carbs (HS4) you can just take the three screws out of the top of the float chamber and lift the top off to see what amount of fuel is in the float chamber. But if you have the SUs with the float in the base it is more difficult. (HIF4) You can however just turn the key on and listen for the fuel pump to run and it should click rapidly at first and then slow down (if it is an SU pump) then remove the top pot with it's piston and spring and blow a "puff" down towards the center jet. If the level is up where it belongs you will see the fuel rise and fall in the jet hole. It takes some practice to do but it is a rough method to see that there is fuel in the float chamber and the level is close to where it is suppose to be. If you don't see any fuel you may try to use a tooth pick in the jet hole as a level gauge. Other than that you would need to remove the carbs and open them up and set the float level.

The HS4 carbs lower the jets to richen the mixture for cold start and the HIF4 has a rotating spindle to supply extra fuel for cold start. My guess is that which ever carbs you have the richening device is not working.

Howard