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MG MGB Technical - Hard starting and uneven plug appearance

My Mk1 3br is being a bit temperamental and refusing to start in the cold after a few weeks unused (its not as cold as northern hemisphere winters - perhaps about 6 deg Celsius).
Doesn't seem to want to start. I have been giving it full choke.
Checked plugs - 2 back ones look normal. Front 2 blacker and smell of petrol. Can I assume the front carb might be too rich - causing flooding?
I've looked through archive - not an uncommon problem and consensus seems to be that it should start with full choke and no throttle.

John
John Minchin

It sounds like your front carburetor is flooding the first 2 cylinders. Remove the float chamber lid and check the level of the float itself. Also, check to see if there is any foreign material between the needle and seat. RAY
rjm RAY

Ray
I will do. The needles are pretty new - the ones with the Viton tips. But I guess with no fuel filter, there is always a possibility of getting some foreign matter drawn in from the (old) fuel tank. I believe some people fit filters into the pressure line before the carbs?

I will see what gives when I open up the float chamber.


John
John Minchin

Certainly the carbs sound as if they are badly imbalanced, but if you get black and wet after giving it full choke and it doesn't start, that would be normal, and it is the back two that are incorrect. If they are dry then that carb would appear to not be giving any fuel.

OTOH if that plug condition is after starting and running up to normal temperature i.e. no choke at the end, then the front carb is very rich as has been said.

The normal recommendation is that for a fully cold start full choke and no throttle is the way to go, pushing back the choke as required, which varies with car and carbs. My roadster with HS4s can be pushed back half way immediately, the V8 with HIF4s can only be pushed back a little bit at a time. However a pal has recently discovered that if he gives it a little bit of throttle as well as full choke, then it catches much sooner, even though the choke is also giving it some fast idle. I'm still trying to decide if my two are the same, sometimes they are and sometimes not, but I have to be very careful with the V8 or it goes into orbit - not good with no oil pressure.
Paul Hunt

Fitting a fuel filter, before the carburetors, is very good practice. I did this to my '67B 35 years ago and have always wondered why the factory waited until the '68 model year to fit one. RAY
rjm RAY

just a thought - http://www.youtube.com/watch?v=pVX_JClyeDQ&list=FLr4Udxf9e9Cq7fxH4V23MWQ&feature=mh_lolz
Nigel Atkins

Not until the introduction of the HIF in the UK at least, which makes sense because of the additional passages and ports in the HIF making it more likely to get blockages with small particles. With the HS by comparison pulling the choke will allow small rodents to pass through.
Paul Hunt

Well, Fuel level in float seemed about right - no crud in needle valve, and little in bottom of the bowl either.

As I haven't adjusted or fiddled with anything since the car last had a run,I'm suspecting I may have a couple of issues preventing starting - thought I should investigate electrics first then worry about fuel mixture second

Firstly, the spark looked "weak" - not sure how big and bright but I've made a better spark with a 9v household battery!

Battery had been on charge (trickle). On no load , voltage at battery 13.1v.
With ignition on, volts dropped steadily to 12.3 over a 1 minute period - recovering to 12.7 when ignition switched off.

After this, I put it back on charge and the green charge light came back on after 45 mins (Its a Battery Doctor)

Today (12 deg C) I checked voltage at solenoid when cranking - 8.8-9 volts. Cranking was slow and was all done after 2 mins of trying - ie wouldn't turn motor over. Checked no load volts at battery - 12.6

The battery is about 5 years old but has only been used in anger the past 7 months - could it be knackered?

When its charged again I will try giving it a helping hand with jumper leads from another vehicle.
John

John Minchin

as always a poor battery(ies) and/or battery connections, leads and earths will hinder starting, same applies to starter solenoid and starter motor - all connections need to be in good condition, clean, secure and protected

see this vid for battery drain - http://www.youtube.com/watch?v=_Uk53AYZ_2o

and http://www.youtube.com/watch?v=kgl7ikq_YOs
Nigel Atkins

Measure the voltage right on the battery posts while cranking, I've seen nearly 3 volts lost in various connections. Bad connections can also heat up with continual cranking and get worse. 12.6v at the battery, off load, when it wouldn't turn the engine over, does sound like connections to me.

The easiest and safest way to check for a drain is to remove the battery earth strap and connect a *volt* meter on its 12v scale in its place. If you have a drain you will see 12v registered. If you have a digital meter this could be from alternator diodes and is normal, so unplug the alternator, and it *should* drop to zero. If you have an analogue meter a full 12v shows a definite drain, the alternator diodes will only cause the meter to register a few volts as digital meters are much more sensitive. Again unplug the alternator and it should drop to zero. If not, then start disconnecting brown wires from ignition switch, light switch, fuse box, starter and ignition relays, and the hazard flasher fuse until the reading *does* drop to zero. You can remove these wires with impunity as having the meter on a voltage range instead of a current range means only a microscopic current can flow from the battery in the event that any of the brown wires touch an earth.

A good spark should be able to jump at least 1/4", a Sport coil more than that. If it barely jumps a plug gap it sounds like the condenser has failed. As a quick test connect a second condenser between the distributor side of the coil and earth and see if that makes a difference. You can leave the existing condenser in-situ.
Paul Hunt

This thread was discussed between 26/07/2013 and 04/08/2013

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