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MG Midget and Sprite Technical - Bringing it back to life

I've just got round to resuscitating the "other" midget after it's having been laying dormant for the last three years.
First mistake was squirting oil through the spark plug holes and leaving it overnight to lubricate the cylinder walls before turning over on the starter to get some oil pressure up. The result was, oil everywhere. Perhaps I should have replaced the plugs before trying that.

However, with everything cleaned up I've now got petrol to the carbs and spark at the plugs but no sign of the engine firing up. I checked for spark at the plugs with a spark tester which showed a spark at each cylinder, albeit a fairly dull red spark.

Stale petrol was a thought, but the fuel gauge was showing empty and I put in about seven litres of fresh petrol.

Suggestions please.

Dave
Penwithian

spray some starter fluid or a teaspoon of gas into each carb, make sure the fuel filter is clean...try firing it up...did you use fresh plugs

Prop
Prop

Dave,

Poor spark at the plugs would seem a culprit. I haven't run my sprite engine for a few years as it's now out but when I did run it up regularly it did start up fine on 3 years old petrol from the tank even though the carbs were a bit varnished and didn't want to idle. I had been sat for 5-6 years and the tank fuel had that very old stale petrol smell so I drained it and added new, then ran it up occasionally for 3 years until I removed the engine.

Points ignition still?
David Billington

Had another attempt at starting yesterday.

This time I squirted Easystart into the carb intakes. It ignited, but was spitting back through the intakes. The same thing happens when I use full choke.

Someone suggested that the timing may be out by 180 degrees, but the distributor has not been disturbed since the car was laid up and it was running ok then.

Sticking valves perhaps? The fuel spits back through both intakes.

Dave
Penwithian


Spitting back through the intake is fairly normal until it runs smoothly. Valve overlap means that combustion gases get pushed back into the carbs which is most noticable when it's spluttering and running at very low revs.

If I were you ...

1) Remove the rocker cover, turn the engine by hand through two revs, and check that all the valves open and close. Check the clearances too. If a clearance is far too big it suggests a valve stuck open.

2) Put the engine at TDC on cyl 1 compression (check for compression with the plugs removed and a finger on the plug hole as the piston rises.), loosen the disi and set the static timing. The procedure is in Haynes. There's a few methods but you basically put a bulb in the low tension circuit and turn the disi until the point open which causes the bulb to light or to go out depending where it is in the circuit.

3) Top up the carb piston oil and check the carb pistons are free to fall. Then do a basic carb setup - throttles open by 1.5 turns on the screws (IIRC - check the value in Haynes!) and jets backed out by 12 flats.

At that point, if you have fuel in the carb bowls and spark at the plugs then it should fire and run.

Ant
Ant Allen

Having just got back from a few days in Germany's green and pleasant land, I've just started trying again to get the Midget to burst into life.

There's still fuel at the carbs, spark at the plugs,and no sticking valves.

However I did gap the valve clearances to 15 thou.instead of the 10 thou. as in the handbook ( a memory flashback to my 'A' series days)

I am also trying to start with the rocker cover removed, breather pipes and vacuum advance disconnected.

Would this prevent it from starting?

Dave
Penwithian

You have to block off the vac hose at the carb end as well.
Brad (Sprite IV 1380)

Just a thought, if you remove a plug, is it wet with petrol? It's possible to get fuel to the float bowl but no further if old fuel has gummed up the pipe to the jet. i know this from experience.
graeme jackson

Brad,

"You have to block off the vac hose at the carb end as well"

Do you mean at the black plastic unions where the breather hoses connect behind the carbs?

As these are sited between the carbs and the inlet manifold, then they must create an air leak at that point unless they are blocked off?

Dave
Penwithian

I'm still pondering this one.

Regarding the two hoses connecting the rocker cover breather to the rear of the carbs/inlet manifold.

An interesting tip in Moss's catalogue (page 131) refers to air entering the inlet manifold (in this case via damaged or missing rubber seals on the rocker cover fasteners) which would affect the running of the engine.

As I have removed both breather hoses at the carb end, surely with these two gaping holes on what appears to be the downstream side of the carbs, the engine is never going to start?

Dave
Penwithian

AS Brad already stated:
"You have to block off the vac hose at the carb end as well."
David Smith

Have I got this right?

I block off both breather hose connections at the carbs AND the vacuum advance pipe?

Dave (being a bit thick)
Penwithian

Dave,
The objective is to stop the engine inlet tract from drawing in air anywhere other than through the carb mouth. Therefore any breather hose attached to the carb needs to be blocked, as does the vacuum advance tube and any brake servo pipe - if you have one - connected to the manifold. The easiest way with all of these is to leave the pipe attached at the carb / manifold end, and to block the other end by pushing a bolt or screw into the open end of each pipe.

Guy
Guy Weller

Thanks Guy, that sums it up perfectly.

And thanks too to everyone else for their input.

Dave
Penwithian

This thread was discussed between 06/05/2009 and 19/05/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.