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MG Midget and Sprite Technical - Won't Start, weak spark

Afternoon.
1500, 1977
Went to start it last weekend (not been used about 7 weeks prior to that), flat battery. Charged battery. Went back to it a few days later. It turned over absolutley fine but would not fire. Took out plugs & cleaned them & replaced (one by one) Checked the spark. It is very week, yellowy/orange. Checked the leads. Replaced condenser & points, set the correct gap. Still no joy. Replaced coil. Exactly the same weak spark.
That's about the limit of my knowledge.
Any help would be greatly appreciated.
Many thanks
Nigel
Nigel Axtell

If weak spark: did you check how much voltage you have on the coil ? Is it close to the battery voltage ?

If this is OK, I will let the Experts guiding you further :)
CH Hamon

When you say weak spark, how are you assessing that?
Mike Howlett

Have you checked the distributor cap for cracks?
Jeremy MkIII

You could try checking the spark directly from the coil, thereby eliminating the dissy cap and rotor arm.
Dave O'Neill 2

if its a 1500 the spark should be better on starting as its 12v until its running check voltage at coil both on starting and when ignition key released .
mark heyworth

Mike: purely by look. when held against the engine block and turned over. The spark is just yellowy/orange

Jeremy - Checked the distributer cap, it's a fairly new one and looks OK

Dave - How do you check the spark directly from the coil.

Cheers
Nigel
Nigel Axtell

Might just be a knackered and tired out battery. Can you try it with a known good battery?
Chris Madge

to check the spark from the coil swap a plug lead for the main lead.
mark heyworth

Nigel,
I'm with Chris, the number of times a problem has been found to be the battery or the battery contributes to the problem or hinders the solution (and/or poor battery or main lead connections).

Unless you have a constant drain item on your Midget like some electronics then a good battery with good connections, well charged, shouldn't be flat in 7 weeks.

Did you recharge your battery slowly or quickly, checked the 'water' levels in each cell, checked the battery posts and clamps and all leads and connections are clean, secure and protected.

Try a known good and well charged battery and see if that works or gives improvements.

I think batteries are often replaced unnecessarily but also that the possibility of an under performing battery is often overlooked especially when it has been recharged.


Nigel Atkins

ETA: -
If problems persists I'd also put back the previous set of CB points and condenser as unless they were bought from somewhere very reliable like the Distributor Doctor then the new parts can be of piss-poor quality and make problems of their own. Generally condensers seem to last decades, but even good quality points can need checking regularly, especially after fitting.
Nigel Atkins

Thanks Chaps, very usefull.
Have to say, I'm not sure how old the battery is. Winter is a nightmare - goes flat quickly. Summer is generally OK. But not much "oomph" in it this year. Regards charging, it's fast charged.
On the basis of the comments I'll try a good battery & see how it goes.
Many thanks
Regards
Nigel
Nigel Axtell

Nigel,
by your reply even more reason to try another good battery. Generally it's better to recharge the battery at a long and low charge rate, some of the really bigger and quick commercial (older?) chargers can kill off a battery that would have survived on a different charger.

Don't forget to also check the CB points gap (and again in a few hundred miles and at services) and possibly return the previous points and condenser if they were fine before as the new stuff (if not bought from a reliable source like the Dissy Doc) can throw up intermittent and difficult to pin down problems later (or sooner, what colour is the lead on the condenser).

And while I'm piling on the pain, some dizzy caps can be rubbish too.

http://www.distributordoctor.com/distributor_condensers.htm

http://www.distributordoctor.com/distributor-points.html

http://www.distributordoctor.com/red-rotor-arms.html
Nigel Atkins

. . . . just thinking out loud . . . . . the 1500 Midget uses a ballasted 12v feed to the coil . . . . on cranking over, if the solenoid is not bypassing the ballast lead, the spark will be weak . . . the fault is unlikely to be the solenoid, but in theory it could give a weak spark on cranking over . . . .
J Thomson

Further developments:
Got the car out the garage & tried to jump it off a good battery.
Tried to turn it over. It didn’t appear to be taking anything from the good battery (which is perfectly OK/charged). Checked the connections again, exactly the same. This time the battery just died as if not connected to anything else. Absolutely dead. No ignition light.
One thing comes to mind, a couple of months ago, the last time it ran I couldn’t get the key out of the ignition. I didn’t want to force it for fear of breaking the key. However it did eventually come out albeit with quite a bit of effort – I was wondering if this has any bearing.
I checked the battery and it read 11.53v
Checked the fuses and they are all OK. Not sure where I go next.
Regards
Nigel
Nigel Axtell

It is possible that your starter motor is drawing an excessively high current when spinning over. That condition would rapidly discharge the battery(ies), and would also give you a weak spark when attempting to start the engine.

Going forward with your problem, if you don't have any electrical diagnostic knowledge/experienceequipment, you have only two options:

(1) Get help from somebody with relevant experience and test equipment, who can methodically carry out fault-finding.

Or,(2) **NOT a sensible option** You can systematically change components in turn, until (maybe) the fault clears.

One test that would be useful is to measure the current discharge from the connected battery with all switches/circuits 'off'. This would confirm (or not) that ancilliary electrical components are not draining the battery.

If it was my vehicle, I would check the battery terminal voltage when cranking the engine over (using a known good battery that is fully charged). If the battery terminal voltage drops much below 10 volts I would suspect a faulty starter motor.

Secondly, I would lash up a temporary 'ignition' wiring loom (battery/solenoid/points/coil) and use that in an attempt to start the vehicle. Doing so totally eliminates the car's ignition switch and wiring from the conundrum.


J Thomson

Thanks for the comment. Interestingly. The starter motor was replaced last year - could this be the culprit
Nigel Axtell

Short answer - get a new good quality battery fitted.

Longer answer - if you have problems with the ignition switch then this could affect everything from that switch such as starting.

Having a battery on jumps leads could be introducing additional connection problems and do nothing to remove any existing issues with the current battery fitted in your car.

11.53v is a very low reading, I think if this is correct after fully charging the battery then perhaps it's time to give up on that battery if you checked the 'water' level and topped up if required before slow re-charging the battery and again checking 'water' level before reconnecting and all connection, leads and wires are clean, secure and protected.

Once you have a good quality fully functioning battery you can move on to solving your starting issues.

A good quality battery fully charged should have enough to start your Midget even after (many) months of not being used (which is bad for the whole car anyway) unless you have something on the car that is a constant drain.
Nigel Atkins

let's assume the battery on the car has a duff cell. *disconnect it - both live and earth*.
Take a fully charged spare battery and attach jump leads direct to the live and earth cables on the car. Now how does it turn over and does the spark look any different?

As no-one else has mentioned it yet, have you located the engine-to-body earth lead, cleaned the connections and refitted it? (ISTR it's on the LH steering rack mount on 1500s?)
Ditto the battery earth lead where it attaches to the bulkhead. These connections need to be cleaned back to bare metal then smeared with vaseline.

David Smith

Good call.

For some reason I missed putting my usual (I thought I had but I hadn't) of checking all connections and wires from battery posts, battery clamps, main leads, wires and all earths, are all clean, secure and protected.

The checking and cleaning if required comes before using the test battery, jump leads or new battery, and includes the checking of jump leads, to get the best transport of the power from a good battery.

Also this is where protection comes in, if using jump leads they need to be protected (insulated) and secure at connections and secure over their trailing lengths.

Poor quality or condition jump leads may also hinder progress especially if combined with other issues and other poor connections.

No disrespect Nigel and this easily could not be the case here but on more than one occasion people have presented me with a spare battery or jumper/charger that they believe to be charged and in good condition and they're not.

Nigel Atkins

David is on it with the earth connection. Many (not all) 1500s earth through the steering rack mount. For some reason it doesn't seem to be ideal. Late GT6s are the same.
On my car I left it in place, but made an additional earth strap between an upper bellhousing bolt and the main body earth on the bulkhead. The more the merrier. (Series Landrovers often benefit from extra earths too btw).
On the jumper cables: if they came in a poly bag from the petrol station or the supermarket they are likely to be utterly worthless. Too skinny and cause far too much voltage drop. Good ones aren't cheap, but they work. Basically the fatter they are and the stronger the clamps are, the better. I made up my own which will happily jump start a 1250hp diesel.
Greybeard

Lift the GT6 and the horn sounded too.

I didn't realise or forgotten that the 1500s don't(?) have an earth from engine/gearbox to body, I'd add one close to starter motor.
Nigel Atkins

Re. 1500 Midget engine/chassis braided earth lead.

Yes, they are a common component of failure, but that wouldn't explain the unlit dashboard ignition light.
J Thomson

If you have had problems with the ignition key jamming, and your ignition light is failing intermittently, then it sounds to me very much like a damaged or failing ignition switch. Excessive resistance there will result in low volts to the coil, even when it is working, and this will give you a weak spark.

Try by-passing the ignition switch with a hot wire direct from battery positive to coil positive, and then check the spark or start it up. This will eliminate the ignition switch and associated wiring.

Kill it by disconnecting your temporary jump lead.
GuyW

Any progress or fault found?
J Thomson

Now have a new battery. Massive improvement in spark, turning over etc. Still won’t fire up. Now looking at fuel. 3/4 tank. Checked one float chamber. Bone dry. Filled float chambers turned it over. Fired 1st go. Promptly stopped when fuel ran out in float chambers. The diaphragm went on the old one about 5 years ago. Replaced the pump all the rubber hoses and the tank as it was rusting through on the top corner. Been fine ever since. The only bit I didn’t replace was the metal section of fuel pipe. The pump came from Moss. How reliable are they. Is 5 years a long time these days! Can’t think it’s a blockage
Nigel Axtell

"Now have a new battery. Massive improvement in spark, turning over etc." - You now know the importance of a good battery in good condition and fully charged - especially when trying to sort anything that involves the electrics.

Why would it not be a blockage (or partial blockage)?

First thing is to check if the petrol is making it to the carbs, easy if you have a clear filter fitted as you can see. Next is how my petrol is getting there and how steady is the flow.

So discontent the rubber pipe that supplies the carbs, quoting Paul Hunt now - "Take the fuel feed off the carb, direct it into a container, and turn on the ignition. It should deliver at least one Imperial pint per minute in a continuous series of pulses with minimal bubbling. If it does that the pump and supply is OK."

Never assume because something is new that it can't be faulty, not working fully or piss-poorly made, a lot of rubber hoses are piss-poor and can split, leak or perhaps crumble inside where you can't see and cause a blockage or partial blockage.

What type of rubber hoses did you buy, braided covered, 1/4" (and 5/16"), modern 6mm (and 8mm)?

Do the flow test and report back for next step, if required/wanted.


Which Fuel pump can from Moss - SU with points, SU electronic, Hardi (electronic), Facet cylindrical, Facet cube, we're not dentist don't have us pulling teeth. :)
Nigel Atkins

"Which Fuel pump can from Moss "

I would think it's mechanical.
Dave O'Neill 2

Well done Dave, I forgot it was a 1500! Doh! I thought all Nigel's had 1275s, would make it easier for my memory. :)

Apologies Nigel.


Nigel Atkins

Morning
Mechanical pump from Moss
Hoses: 1/4” and 5/16” braided
The fuel is not getting to the carbs.
I have disconnected the inlet supply hose, connected an inflatable toy stirrup type pump and blew back down the line regarding blockages. There was plenty of “gurgling and bubbling.
My previous comment about reliability of parts confirms Nigel’s remark about never assume etc.
The hoses I replaced all look in good condition.
The hose that comes up round to the inlet which is a fairly tight radiu has a little crazing on the outer rubber casing.
To my mind it tends to point towards the fuel pump.
The only other thing I can think of is the rigid fuel line under the car. Moss catalogue says the old stuff is prone to rust either inside or outside. The air/blowback test doesn’t suggest that. However that was “dry”
I could check that by getting fuel down the inlet pipe.
Any other suggestions?
Nigel Axtell

Has that pump worked since you replaced it? There are 2 versions of the mechanical pump with different length lever arms. The longer arm pump uses a spacer between pump and block. If you fit a short lever arm pump with the spacer it will still work, but not very well as the arm doesn't properly reach to the cam lobe.

One problem with reluctant-to-start 1500s is that you have to turn the whole lump of the motor over on the starter, just to operate a tiny fuel pump lever. So a poor condition pump puts a disproportionate high load on your battery condition.

You can check the fuel pump by unbolting from the block and operating the lever by hand. If you are lucky you might even have one of the earlier pumps with an external lever for priming!
GuyW

Whichever version of mechanical pump you have, if it has a cover secured with 5 screws (like mine) you're in luck. There is a rebuild kit available with the poppet valves, springs and all seals and it's an absolute pushover to fix. Dead easy.
Many of them have the cover swaged onto the pump body though, which is not so easy.
These AC Delco pumps are still in production as loads of small static engines use them to this day. From memory it's a Type Y, but as Guy says there are slightly differing variations on the theme.
Greybeard

The pump has been in 5 years & has been working fine. Took it out this afternoon & it is absolutely fine . Tested it with a couple of bits of hose a resovoir of fuel and operated the lever - worked fine.
Now stumped as to what the problem is.
Nigel Axtell

ETA: (I'm too late with this) I'd follow Guy's advice.

Also I'd not trust 5 year old braided hoses, I'd take them off the car completely and blow them through, in both direction, into a glass jar to to see if any specs or crumbles of rubber come out. Short lengths you could look through for large blockages or shine a small needle or pen light if you have one.

ETA: (I'm too late with this too!) Subject to safety you could remove the existing supply of fuel to the pump and replace it with a temporary direct supply of fuel to the pump in situ to prove it's still operating well.
Nigel Atkins

Good that the pump works. Do you maybe have a blockage at the carbs inlet? Or as you wondered, some damage to the rigid fuel line?
Or is the pickup pipe in the tank compromised in some way, which has been the subject of some speculation with Les's troubles with his 1275? A 1500s pump will definitely be unhappy sucking air and the test you have done was drawing from a reservoir of fuel (a can or bottle maybe?)
How much fuel is in the tank? If there's not enough to cover the pickup pipe you could try filling it right up. If that does the trick a bad pickup pipe starts to look like the cause. Apparently it's possible to sort it out. I've never done it myself, but I posted a link in Les's thread that says it can be done.
Greybeard

Surely if you unbolt the pump so that you can operate the lever by hand, keep the input line from the tank connected but disconnect the outlet pipe, then operate the lever. If no fuel comes out then the fault is upstream ( tank pick up or fuel lines). If fuel comes out then reconnect the delivery pipe at the pump, but disconnect at the carb. Operate the pump again. If there is a blockage you should be able to pinpoint exactly where it is.
GuyW

"Checked one float chamber. Bone dry"

Is it just one carb that isn't filling?
If so, then you may have connected the pipes wrongly between the two carbs. Maybe carb 2 is plugged into the overflow pipe of carb 1 by mistake?
GuyW

Morning
The tank is relatively new - about 5 years old. Bad pickup would be disappointing! There was just over half a tank of fuel, I topped it up with a gallon of fresh, so it's showing 3/4 full(ish)

Guy - I think I'll take the pump off again & try operating it by with the inlet pipe connected - should have thought of that when I had the pump off.
The pipes connected to the carbs are correct as there had been no problems prior to this "sudden" failure

Cheers
Nigel
Nigel Axtell

Hi,

I will do what the previous said : disconnect the outlet of the pump from the rigid pipe, put it into a container, and put the ignition switch on; but keep everything in place on the car.
Maybe you did and I didn't get it :)

Regarding the "only 5 years old pump", you can see in a thread close to yours that my pump had dirty points in 15 years, but only one or two thousand miles...
CH Hamon

Cedric

Nigel's car is a 1500 and has the mechanical pump driven from the engine (camshaft).
Dave O'Neill 2

No contact points ? Boring.... :D

I still need to learn more before helping then :)Thanks ;)
CH Hamon

It's worth taking the float bowl tops off the carbs and making sure that the needle valves are both dropping, allowing fuel to flow into the bowls...sounds like one could be jammed in the raised, 'off' position.
R Cohen

Yesterday I took the pump off put a spare piece of fuel pipe (new) that I had & pumped the lever by hand. Within a couple of pumps or so fuel came out of the pipe. I conclude that there is no blockage, air problem or leak from the tank to the pump.
I then re-fitted the pump used the same piece of tube to discharge into a petrol can, turned the engine over a few times. Not a drop came out.
Tonight’s exercise is to take the pump off, re-connect the proper fuel line to the carbs/float bowls & pump the lever by hand again to see if it pumps up to them.
Also peer into the hole to see what’s going on with the cam. Anyone know if this has been a problem
As previously stated, the pump was replaced about 5 years ago & had worked faultlessly until two or three weeks ago.
Now running out of ideas.
Nigel Axtell

This is certainly odd!
Presumably the pump lever isn't broken or it wouldn't have pumped when hand operated. But the part of the lever that bears onto the cam lobe could perhaps be worn. Or possibly the cam lobe itself has worn. If that were the case then it would mean either replacing the camshaft complete (the other cam lobes for the valves could be worn as well) or replace the pump with an electric one.

But there may be other simpler possibilities. Perhaps you have the short lever pump that needs no spacer? Or, I once had a pump that appeared to pump fuel ok, but it couldn't keep up with fuel demand on a running engine. It turned out it had a split in the pump diaphragm. It was fixed at the roadside with a piece cut from a plastic carrier bag!

GuyW

Afternoon Guy
Lever's not broken. It's a long lever/no spacer. I'm thinking either worn cam lobe or the pump is "partialy" failing. The diaphragm went on the previous one a few years back. Changed like for like and as I say all was well until a couple of weeks ago.
When putting the pump back I have to keep it push back on the studs to get the bolts on. Which suggests to me that the lever is pressing against the Cam
Nigel Axtell

Yes, but is it pressing too tightly onto the cam so there is less movement, less pumping action?

The "long arm" ones are supposed to use a spacer. It isn't that easy to be sure which you have without physically comparing them. The puzzle would be why it worked for a while but has now stopped, unless ( and this is now pure speculation):

the long arm version used without a spacer put excessive pressure onto the lobe of the cam shaft, causing it to wear rapidly to the point that it now no longer activates the pump.

Engineer input needed here to say if that is likely, and how would one check?
GuyW

It might be worth taking a few measurements:-

Distance from the block face to the camshaft lobe - both extremes.

Distance fro pump face to lever tip - both ends of its stroke.
Dave O'Neill 2

Incidentally, I once worked on a tvr engine where one valve wasn't lifting at all. On inspecting the camshaft just one cam lobe was worn down completely circular, with no discernable bump in it at all. The others were all ok. Why just one had worn to that extent I never did discover.
GuyW

Guy/Dave
Useful comments there.
The one that I replacced years ago was essentially the same (same length lever). The one that came out looked like the original and didn't have a spacer.
That is a good point about wear.
I'll do some measurements with the pump out
Thinking about the wear comment, could there be a possibility that the lever has worn. Metal quality may not be as good
Nigel Axtell

I would certainly check over the internals of the pump first, as Grey suggested. If the diaphragm is split, or maybe if one of the valves is sticking, it may still pump fuel when activated by hand, but not when operated by the cam shaft. The likelhood is that when you test it by hand you are moving the lever through a bigger discplacement than when the cam operates it. The cam movement will be fast, but really quite slight. This could explain why it seems to work when tested, but not when on the car.

GuyW

This thread was discussed between 09/09/2019 and 10/10/2019

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