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MG Midget and Sprite Technical - Starting problem

This is getting worse, and the time has come to fix it. When starting from cold, with the usual full choke, the engine fires once and stops, while the starter pinion spins down. Bang - wheee. It often takes 3-4 goes before it catches. The other day it almost didn't start at all, as it needed 10 pulls on the knob. It seems as if the ignition is too advanced and pre-igniting, but the car was checked on Janspeed's rolling road last year and the timing and carb settings are still the same. There is no detonation, and I run it on 99 octane. Today I tried retarding the dizzy a bit and that made no difference, apart from destroying the throttle response. I have been using the Powerspark ignition module, and tried going back to the old points - worse if anything.

The setup is:
998cc, HIF44, A-Plus dizzy (for 998), Kent 276 cam, big valve Metro head, Maniflow medium bore exhaust.

I tried changing the vac advance connection from port to manifold and back - again no difference. I don't know what else to check.
Les Rose

Les, It's not been set up with a ballasted coil system has it? Could be a fault at the ignition switch, so coil is only receiving power when the switch is in the starter position, but not when in normal run position?
GuyW

Guy Isn't Les's car a frogeye with a mechanical pull starter?
Bob Beaumont

Guy, you are talking heap big magic! I put my car on the profile pic so I don't have to explain.... :)
Les Rose

Bob, Les, yes I know its a frogeye and therefore SHOULD have a pull type starter solenoid and SHOULDN'T have a balasted coil but given the extent of other modifications I just wondered if these had also been "upgraded".

More telling perhaps is that it does eventually start, so maybe it is a problem with fuel level in the carbs, until its been turned over a few times. Enough residual fuel vapour in the inlet tract to get an initial cough from it, but not to run?
GuyW

Bob, Les, yes I know its a frogeye and therefore SHOULD have a pull type starter solenoid and SHOULDN'T have a balasted coil but given the extent of other modifications I just wondered if these had also been "upgraded".

More telling perhaps is that it dies eventually start, so maybe it is a problem with fuel level in the carbs, until its been turned over a few times. Enough residual fuel vapour in the inlet tract to get an initial cough from it, but not to run?
GuyW

Valuable point Guy.May be worth checking fuel pump delivery. I gather its an electric rear mounted one.(article in Rev Counter) Are the filters blocked? Crud from the tank?
As it fires it may be less likely to be a spark problem.
Bob Beaumont

Les,
have you tried a bump start instead of using the starter.

There was another car that wouldn't start when cold but would easily bump start, starter sounded fine and started the car at other times so I among others discounted the starter as it had been previously serviced and sounded good. Like yourself the owner had checked and tried lots of things.

After going through everything at least twice against the prevailing advice the owner fitted a new starter, he was right as this solved his problem, the previous starter must have just been too old and worn for the extra effort required.

Nigel Atkins

Yesterday I couldn't get a neighbour's petrol mower started after sorting a few issues from poor storage and wet fuel. As it wouldn't start after checking for spark another neighbour helped as we attempted to sprayed some starter fluid (de-icer) into the carb and pull start that required two people. We got a slight start on but it only ran for seconds. My neighbour asked if I was sure the petrol was getting through and I assured him I'd striped cleaned the carb and checked fuel delivery.

I took the very fiddly carb, linkage and air filter arrangement all apart again to check for errors and immediately found the carb was bone dry, if I'd had just listened to my neighbour and tapped the carb the float needle would have unstuck itself and I'd have saved time, effort and a few more grazes on my hand. Once again I thought I'd checked the bleedin' obvious but hadn't.
Nigel Atkins

Try pulling on the starter - ignition off, and switching on the ignition as the engine is spinning. Check bob weight springs are OK.
f pollock

Morning folks, and thanks for your ideas. My replies:

Fair point Guy, but no the coil and starter switch are standard.

I checked the float level in the single HIF44 only a few weeks ago, but will have another look. Actually I think the symptoms match this explanation, as the engine fires after some churning. That reminds me, the pump clicks for a while when turning on the ignition. The fuel level in the carb may be dropping when parked. I usually wait until it stops, only 2-3 seconds or so. This doesn't help the starting though.

The fuel pump is a new electronic one from Burlen. There is also a new filter into the carb and none in the tank.

I serviced the starter motor a few years ago, and with very low mileage in mind it should still be fine. It spins the engine lustily. I'll look at it again if nothing else works. Oh well back to the garage.....

Les Rose

New electronic pump from Burlen - always worth checking new parts work well and the electric connections are good. Personally having a fit 'n' forget Hardi I'd be checking the overpriced SU electronic pump for consistent flow rate and force.
Nigel Atkins

Les,
You could try adding a cc or two of petrol down the carb throat before you try to start it when it’s cold.
If it fires and runs for a few seconds then you know it’s a fuelling issue.
I do find that my HIF6 fuel needle does seem to stick if it hasn’t been run for a while but mine runs then until it empties the carb.

R.
richard b

The choke system on an HIF44 includes two O rings which are prone to deteriorating and might be worth checking, as a simple elimination step.
GuyW

Jep, my 1 thought... choke
a.o. arnold

I had the carb off yesterday and reset the float height. I found that the bottom cover of the float chamber is warped, so is not tight all the way round - only at the screw positions. I made a thick gasket, as a temporary fix, as the rubber seal won't go back in. I always find these things expand and can't be reused. Last year all the seals were renewed, and the car only did 1200 miles since. I am not keen to do all that again (getting the return springs back on is a pain). Today the starting was slightly better - only 2 pulls. Fuel pump only ticked for a couple of seconds. Tomorrow I'll go over to Burlen for a new cover and seals.

I also think the piston is sticking, especially when hot. The revs don't drop as quickly as they should, and there is still the erratic idle. I found a video by AC Dodd that explained that there is a fast drop damper available as an option, but it's just a standard one that's a bit narrower. So I turned a smidgen off the plunger in the lathe. I have a long run booked for Thursday so we'll see how much difference that makes.
Les Rose

I've no idea if it's true but I saw recently that carb cleaner can cause the rubber seals to stretch/expand.

With the quality of some rubber you might as well use the rubber bands the postman/woman discard as litter.
Nigel Atkins

Tried the dribble test today. After priming the carb, starting is instant, so it's fuelling that's the problem.

Just been to Burlen. The carb bottom cover is well known for warping but they are out of stock until July. The seals are also well known for expanding, especially if the cover doesn't seal. I also asked for the fast drop damper rod but, guess what, out of stock. I can only try a new seal but I'm fairly sure it won't work. I'll replace the cold start seals while I'm at it.

I might try lapping the cover down on the surface plate, but difficult as there are two pins sticking up.

The idling still doesn't drop fast enough.
Les Rose

Les

I recently acquired a float chamber top for a reasonable sum off ebay. I got the impression it was a hobby trader as he/she had several on sale.

It seems to be in good order and fits the carb well but I've not tested it on the car yet.

Might be an option given the price and current unavailability of new ones.

Colin
C Mee

Les,
Glad the ‘dribble’ test worked !

With regard to the return to idle I suggest ensuring the piston drops nicely with a clunk without the damper.
Then try with the damper - if it’s at all bent it could be slowing it. Assume you have a fairly strong throttle spring ?

R.
richard b

Those covers on eBay are sold out - not surprising.

Yes the piston drops with a clunk, with or without the damper. I tried an extra throttle spring and it made no difference. I need a new damper when they come back into stock.
Les Rose

The two pins that stick up from the bottom cover are only to prevent fitting the wrong way round, and it's marked for that anyway. So I filed them off and lapped the thing down on the surface plate. The starting is much better, and the pump only clicks once or twice when switching on. So that problem is probably solved, and I will probably not bother with a new one. For the damper rod, turning a bit off the plunger seems to have made it worse. I can't understand how that can be, but they have the correct ones at Minispares so a new one is coming next week.
Les Rose

Les, just re-reading this and wondering if the erratic idle is a clue. Could indicate an air leak, which might (as in might!) also explain slow rev drop. Certainly makes starting harder.

Usual leak source on A series is manifold gasket where it is thin above and below the port. If a brake servo is fitted that can also cause a leak if faulty but most midgets don't run one of course.

With HIFs the overrun valve in the throttle disc (where fitted) will also cause slow rev drop/high idle
Paul Walbran

Thanks Paul, but I have been round the air leak loop many times for years and eliminated all possible sources. New throttle shaft, gaskets etc. I removed the horrible overrun valve and filled up the disc. No servo of course.
Les Rose

I have fitted the new damper rod, and although the engine is more responsive, the idle is still erratic. Curiously the new rod is ball jointed at the cap end, so is self-centring. The old one is rigid.

I can't believe this is caused by an air leak. Blipping the throttle can get the idle to settle, and an air leak would not do this. I can find nothing wrong with the cable and linkage. However I am wondering again about the crankcase breather valve. It has a new diaphragm and plunger, and all the hoses are tight and in good condition.
Les Rose

Worn butterfly spindle perhaps? Notorious for giving erratic idle as the worn spindle randomly settles and seals better or worse each time it is operated, with varying angles and tensions of the throttle cable and the return springs. You could try capping the exposed ends of the spindle with blobs of silicone and see if that stabilises things.
GuyW

This thread was discussed between 14/05/2022 and 26/05/2022

MG Midget and Sprite Technical index

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