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MG Midget and Sprite Technical - Hot start failure

A strange problem on my 1275 RWA? I had a previous hot start fault that turned out to be coil failure. I've replaced (less than 1000 miles ago) the coil, leads, plugs,dis cap, contacts and rotor(not the condenser as the screw was worn and it appeared ok), but a problem has re-emerged.The battery and voltage is ok, since fitting an alternator. There are two symptoms:

A slight intermittent misfire when applying the throttle during driving or on tick over when hot.
This is reduced by leaving the heater on to draw off heat.

When its hot and wont start, its sounds like the starter motor isn't under load (high speed spin noise that reduces in pitch as the engine cools down).

If I leave the bonnet open for 30-50 minutes after a few tries it will start and run ok, as long as I dont stop (or stall), so definitely a heat problem. Only smells of fuel if I try choke or press the accelerator while trying to start ( so probably not vapour lock).

Are the problems related or 2 separate issues? Starter motor solenoid and an iffy HT lead or duff plug? All help appreciated.

Spec:

1972 RWA 1275cc
Moss Sports manifold (insulation wrapped) and exhaust
Pancake air filters
Alternator
70-80psi oil when running
Temp max on coolant gauge never exceeds 30%
Engine is a recon with 29k on clock
M A Pollard

I had this problem, cured by a new condenser! I had a similar problem on my ancient Hayter mower and a new condenser solved that too......!
Bob Beaumont

What about electronic ignition such as one of these?
http://tinyurl.com/c92nu6f

Jeremy
Jeremy 3

When you say it won't start when its hot, do you mean the engine is turning over and it won't fire, or is it that the starter motor is not engaging the flywheel and not turning the engine over?
In other words, when its hot, when you turn the key ( and I'm going to use some very technical terminology here) does it go "Wheeeee" instead of the usual Ur-ur-ur noise? in which case, it's your Bendix Gear mate.
M J Chapman

Bob Beaumont; the condenser is the only thing I didn't change. Even so, for a few hundred miles it was all ok, but gradually got worse like the last time.

Jeremy 3; I'm considering changing to electronic ignition.I've been looking at the Powerspark conversions, which are reasonably priced compared to other brands. Simonbbc.com seem to be very reasonable on prices for all electrics (saw it on a previous thread).

M J Chapman; it's high speed / pitch (no friction) when hot, but seems to engage as it cools. I suspected that it could be the solenoid on the starter. Guess I'll be investing in a heat shield wrap for the new starter.
M A Pollard

Hard starting and starter issues esp when hot....

Id be looking at dirty rusty oily grounds...esp your mesh strap from the tranny to the car


To get a better idea... Run the car hot agian and then check for a nice crisp blue spark at #1 spark plug... The yes or no answer will tell you where to look next

Also check that you have the correct spark plug temputure ratings....if your plugs are a hot plug you could be getting some detention and that can make the starter act funny

If you are getting a nice blue spark...id look at a sticky choke and/or a vacume leak.

Anyway a few thoughts id have

As to the electronic ignition... Im no longer a fan....the points and condensor are easy, cheap, and work great for at least 30xxx miles...(how many miles do you drive) and if the dissy is that bad that point wont work as well...and you need electronic to even out the bad spots....then have the dissy rebuilt...it wont cost that much more for a perfect operating dissy then a cheap china made gimick

Prop and the Blackhole Midget

"I'd be looking at dirty rusty oily grounds...esp your mesh strap from the tranny to the car"

What Prop is suggesting here is that the soil in your drive is pretty oily and the transvestite strapped to your car isn't doing it any good either.

Actually as he suggests, a poor earth connection may be reducing the voltage at the starter sufficiently so that there is not enough " oomph" to throw the bendix gear out and engage on the flywheel - like what happens when your battery is nearly flat.
M J Chapman

Definitely recommend electronic ignition - mine's a Piranha unit and is donkeys' years old but works a treat. It's tucked up on top of the o/s wheel arch, neatly out of harm's way and relatively cool. I wouldn't go back to points now.

Good luck with the starting issue - you've plenty to have a go at!

Jeremy
Jeremy 3

*******What Prop is suggesting here is that the soil in your drive is pretty oily and the transvestite strapped to your car isn't doing it any good either******

Whew....thank god someone understands me....thats exactly what i was thinking....hahahaha

Prop
Prop and the Blackhole Midget

MA,

Did you get a chance to test for a blue spark on #1 spark plug after getting the engine good amd hot??

What happened??

Prop
Prop and the Blackhole Midget

Prop: I haven't had a chance to check the plugs yet. Power doesn't seem to be the problem, scince the battery can easily crank the starter motor 10+ times without diminishing the voltage when hot. The starter turns, but does not engage. Possible heat damage to the windings or solenoid?

The other thing I've noticed (not sure if it's normal), is that when I cold start, at the pre ignition stage of turning the key, the fuel pump can be heard clearly chugging away. This does not happen when hot starting. Incidentally, the fuel pump is mounted by the rear n/s wheelarch.

Has anyone fitted a Powerspark conversion? It's cheap, so is it reliable?

M A Pollard

Hmmm... So the starter is spinning but not turning the engine over...is that correct.??


Id say pull the starter and give it a Good bath in gasoline... But do not oil or grease it...keep it dry and clean...while its out have a shop test it....here we have autozone parts stores that will test for free...im sure you have similar places that will test for free

Dont get distracted by the fuel pump just yet...make sure you have a good blue spark at the plugs first when the engine is hot...it appears the pump is working fine to me....having a blue spark or no blue spark is going to tell you alot and its easy to check


And dont make the conversion to electronic till yyou source the problem you now have as that will only mske diagosics even harder....work the problem 1 st

Prop


Prop and the Blackhole Midget

Sounds to me as if you have a valve (or valves) which are sticking open when it gets hot. Hence the misfire and difficulty with restarting. And with valves stuck open the compression is reduced so the starter is spinning the engine over more easily and sounds like it is under reduced load/

Try checking and possibly slackening the valve clearances a bit.

The wrapped exhaust manifold can result in too much heat retention, so may not be a good idea.

Fuel pump not audible when starting from hot because carbs are already full. They only click when the float chambers are low.
Guy W

Agree with Guy about valve clearances judging by the slight misfire as it gets hotter and refusal to start, plus the unloaded starter impression. If this is the case, you need to check clearances ASAP or you may end up with a burnt valve or valves.
I'm not a fan of heat wrap as it tends to keep heat in the head which may be exacerbating the possible valve problem.

Bernie.
b higginson

Well i was headed that direction of the valves,

but i figured the igniion was fastest and easist to check 1 st
But yeah... A shot gun approach will work just as well, after you check the valves go ahead and pull the timing cover and check for a worn chain, then look a the fuel pump, then come back and look at the spark...justa random flip a coin appoach will work fine


Prop and the Blackhole Midget

Prop,
Its not just a random approach. Its a matter of carefully reading the symptoms as described and identifying what fault or faults might explain that specific condition.
Guy W

Thanks for all the help guys!
I've just fitted Powerspark electronic ignition. 1st turnover there was a thud (like in gear). Same again 2nd start, then 3rd attempt it roared into life. It's starting first time every time for now and seems to be running better. So that's one problem solved (hopefully?). The thud though does suggest the solenoid / shaft sticking. I'll have to carry a hammer or large spanner until I get a new starter motor.
M A Pollard

Im not so certian you have a starter issue...i still dont understand what the starter problem is you have

But on the lucas starter its not like a normal starter...its designed to kick out as soon as the engine starts to catches fire...which can be a hassle if the ignition is not in top order

They take some getting used to... Thats why a super clean starter oil and grease free is so important
Prop and the Blackhole Midget

This thread was discussed between 25/07/2012 and 12/08/2012

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