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MG MGB Technical - Hard starting 1979 (US Version)

Replaced an erratically firing pertronix and adjusted valves and fuel mixture at the same time. The car runs beautifully but has been hard to start since. It requires cranking for minutes before fuel smell is noticeable and then it finally starts.

Plugs and fuel filter are new. Ignition timing is properly set. Stromberg needle is set at the base line, with the washer flush with the piston base. Once the car has started, it starts instantly throughout the day.

This car has a manual choke that was adapted, not the original automatic choke. Choke cable is properly adjusted.

Any ideas will be appreciated.
Glenn Mallory

Glenn: It seems you are getting sufficient fuel. Try starting it (when cold) without pumping the accelerator then when the engine begins to start then press the accelerator. Perhaps you are inadvertently flooding it.

My 79 has a Weber and a Lumitronix ignition and I do not press the accelerator until I crank the engine first. Starts right off.

Let us know how this turns out

Cheers

Gary
gary hansen

If it only starts when it appears to have flooded it seems to me that some cylinders could be weak from a vacuum leak. Does it run smoothly immediately it starts? Or roughly getting smoother as it warms? Or obviously rich i.e. hunting? Do you use full choke to start? Do you push it in at all as soon as it catches? Did it cold-start fine before? If so then you must have changed something for the worse along the way.

Cranking with a non-starter with the choke out will usually flood it pretty quickly, and that's when you get the fuel smell especially in a garage. Then one usually has to push the choke in and open the throttle wide and crank some more, being ready to release the throttle and half-pull the choke when it catches from the excess fuel having been blown out.

Starting with the choke out, which should also give some fast idle i.e. open the throttle a bit (have you checked that?) hence no throttle should be all that is required for a cold start, a hot start with no choke normally requires a bit of throttle.
Paul Hunt

Paul,

There is no rough idle or running condition once the car starts. Vacuum ports seem to be tight as there is no "hunting" condition. I agree that it seems to be flooding. Full choke is required now that it is getting colder and the high idle seems to be be set properly.

What got changed was the replacement electronic ignition unit as the previous one was firing very erratically. Valves were also very loose and now are set properly with the attendant quiet running.

I did weaken the mixture as the needle was set to extreme rich position. The car runs very well... once it starts.

I will pull a spark plug and check the spark at initial turnover.
Glenn Mallory

'Hunting' to me is a regular and rhythmic rise and fall of the revs at idle and is due to a rich mixture. A vacuum leak would cause a weak mixture which usually causes an irregular engine beat with a 'splashy' sound in the exhaust.

Did you have to change the timing with the new trigger? If so did you check the timing before you changed it? What is the timing now?

Have you checked/adjusted the mixture?

The rocker cover, oil filler cap, and all the emissions plumbing must be present and correct, or removed in such a way that no vacuum leaks (which can occur at a number of places) are present.
Paul Hunt

Timing was impossible with the old trigger. It was highly advanced and erratic. The car has been timed to spec and the harmonic balancer checked for integrity.

Mixture was leaned from raised needle to flat washer level with piston bas position. Had it checked for emissions but still comes in rich.

Compression is OK (checked warm). Once started, the Caria very even and strong.
Glenn Mallory

You changed three things, you must be missing something somewhere. Are you sure your manual choke is actually enriching the mixture? Running rich doesn't chime with having to crank for ages until you get a strong fuel smell, and only then does it start. Are you sure you are getting a spark to all cylinders during this long cranking?

'Caria'?
Paul Hunt

This thread was discussed between 14/10/2013 and 26/10/2013

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