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MG Midget and Sprite Technical - High Idle 1275 after air pump removal

I have learned something really important today that I will take into my future MG jobs that I tackle.If you are going to do a project, don't take 2 months to do it, becuase you are going to forget where your at.
I finally got the Cars on and cables connected to my 73 1275 A series midget.
It was turning over, but would just not start. I took a look to see if I was getting a spark, which was good, pumped the carbs, but still nothing. Then after taking a look at the manifold, I saw I had barely tightened the 4 screws that sit between the carb and the manifold. After doing these up, the car started straight away, though it started to idle at 2250. While I replaced the head and head gasket, I was unable to get the air pump connected, so I blocked the holes in the head. Would this lead to my problem with high idling and if so, can I tune the fuel mixture to get it idling at 850 without changing needles or should I go out and get the parts needed.
Thanks for your help.
Allan
Allan Jacks

Allan. You need to get a good book on the SU carbs and understand what you are doing.

First, "pumped the carbs" is meaningless. On carbs having an accelerator pump, each time you open the throttle you squirt a jet of fuel into the carb throats. SU carbs, however, do not work that way because they do not have an accelerator pump.

First, the air pump is connected to the exhaust system and has little, if any, effect on the intake system. Leaving the holes for the air pump attachments unplugged will cause an exhaust leak in the engine compartment, but should not affect the intake system.

The high idle can be caused by several things, with the three most common being induction system air leaks, improperly adjusted carbs, and incorrect ignition timing.

Check for air leaks by spraying some carb cleaner or WD-40 around all of the induction system while the engine is at idle. If the sound of the engine changes (idles faster/smoother) that indicates an air leak that must be corrected before any other tuning can take place.

The carb linkage can be out of adjustment. If it is somewhat jambed up, it can cause the throttle plates to not shut fully, resulting in a high idle. You need to check out the system and set it up properly from scratch. The factory workshop manual covers this and Paul Hunt's The Pages of Bee and Vee has a good description of how to set up the carbs. Between the two you should be able to set the carbs up properly. If not, you should be able to find out what is preventing you from doing so.

The amount of ignition advance will have a strong influence on the idle speed. If it is over advanced, you will have a high idle which will be hard to bring lower.

Check these areas out, in the suggested order and there is a good chance you will find where the problem lies. If not, report back with what you have done and what you have found so we may begin from a common basis of understanding.

Les
Les Bengtson

I have some cleaning to do. The Choke was stuck on. I put the cable surround for the Choke back in the hole, which loosened the choke and then idle dropped. I will have to tune them, but its looking good.
Thanks,
Allan
Allan Jacks

Allan. Glad you got it sorted. I have had this happen to me once and have heard of one other case of the choke hanging in the downward position and causing a high idle. Thus, not a common problem, but one which has happened in the past. But, you got it sorted and that is a good thing. Congratulations to you. It was well done.

Les
Les Bengtson

This thread was discussed between 17/04/2009 and 20/04/2009

MG Midget and Sprite Technical index

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