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MG Midget and Sprite Technical - engine cutting out?

Went out for a run in my 1500 midget and all was well until after about twenty mins engine temp is about half way and engine just cuts out. Car would then not start, left it alone for half an hour car start and runs perfectly again drive it for another half hour then the engine cuts out again ? Any help would be appreciated.
C Carter

Well, since it is a warm day, it could be fuel vaporisation.

What does the rev counter needle do as it cuts out? If it thrashes around then it is an electrical problem.
Guy

Just before it cuts out you can her the engine starts to struggle and loses power rev counter is not erotic and don't see how an electrical problem would be related to the heat which this obviously is as once engine reaches temperature it happens.
C Carter

No, I don't find rev counters erotic either, but I believe some do.

But electrical problems can and are often related to the engine getting hot - insulation on wires soften, components go faulty, rotor arms fail etc. so don't just dismiss that.

But in your case, if the rev counter isn't erratic, then it is more likely to be fuel related. Fuel vaporisation is a real possibility.



Guy

I was thinking that maybe it could be fuel related could this be air getting into the fuel line would this get worse as the engine get hotter
C Carter

If it cuts out and stays unstartable then it is most likely electrical.

If it cuts out and then after standing (cooling, if left long enough) for a bit it can be restarted then Guy is correct and could be due to fuel vaporisation.

Do you have a heat shield properly fitted?

If you look down the list of threads, there is one started by Jue Williams who had engine running problems that were due to a missing heatshield.

Usually if the car is moving it is not so much of a problem but if sitting in traffic the carbs/fuel overheat and then the troubles start.

If you do have an effective heatshield then I am stuck for the moment!
JB Anderson

If the car just "cuts out" - ie no coughing or spluttering - then I would suspect an electrical, heat related, fault.

All joking aside, if you've got conventional points, then the problem could be the condensor getting hot and going resistive until it cools down. Just as likely, coils' internal insulation can break down with heat and fail. Just some suggestions, but . . . been there, seen it, bought the t-shirt, cap and book (!)
Andy Hock

another vote for condenser or coil
David Smith

What the condensor, I thought we killed all that kind of talk 5 years ago :)
Robert (Bob) Midget Turbo

Rev counter can be erratic but at any heat!

Sounds like you need a heatshield, but before you fit it do cut out a handshaped corner at the front so you can get the dipstick out when hot!
rachmacb

Hi, Bob - Yeah, I know the 'faulty condensor' is a running joke. But they can and do go faulty causing rough or non-existent engine running. As do coils.

One of my earliest memories of working on my Midget was when the local 'Home Tune' mechanic was stumped with bad engine running - despite him having fitted a new replacement condensor as part of his servicing the car. He changed it for another new one and, hey presto, everything came good.

Andy Hock

Its only a joke mate cos a few years ago anytime anyone had a fault and came to these boards the answer they were generally given was CONDENSOR. It used to drive me mad and I thankfully have convinced people that 999 times out of a 1000 it is NOT the CONDENSOR!

But occassionally it does happen when every day in the month is a sunday LOL.

If anybody wants a laugh and are particularly bored vist the archives of a few years back and search condensor. It's embarrassing!
Robert (Bob) Midget Turbo

I have just been reading back through old articles and yes the answer to everything at one point was the condensor. However on this occasion I am thinking that you might be right so this week I will be ordering a replacement condensor. Where is the best place to get one of these from? I dont mind paying more for a better quality part.
C Carter

Great stuff C.C for the benefit of us all change the condesner and let us know if that cured the problem before you do anything else. You could make history?

Must admit I have found 2 faulty condensers over the last 45 years and one of them was similar to yours however you have not convinced me that the problem is not fuel related so lets see how you get on.

I hope you noted the names of the posters in the past!
Good reading isn't it!
Robert (Bob) Midget Turbo

Rach,
I wasn't suggesting that the rev counter might be erratic because of the temperature! Or that an erratic rev counter could be causing the problem.

The point is simply that a rev counter needle that flickers as the engine dies is a good diagnosis that the fault is with the LV side of the ignition circuit. It is just a good way of narrowing a fault down so that one doesn't start tampering with an previously good fuel system!

(and the converse is also true - if the needle just dies without violent flickering, then suspect the fuel system)
Guy

I will change the condensor and then report back. It is very good reading....... Knocking noise in rear axle solution change condensor lol
C Carter

LOL Guy - nor was I - just whinging about rev counters ;)! That's kinda why I do try to persuade people to "get used to their particular car" before doing any changes, as, they are all erratic in their own particular way, and, without getting used to the car, then, it's hard to know what's right and what's wrong :)

Apparently, for example, I was told yesterday, that the speedo, when it reads 90mph, really only means 60mph .... hmmmm - not convinced about THAT one!!!!!!!!!
rachmacb

if you're getting one this looks like the place to get it from - http://www.distributordoctor.com/distributor_condensers.htm
Nigel Atkins

Bobert,
Just because some of us had fun suggesting condenser replacement to cure axle problems does NOT mean that condensers do not fail regularly in non-obvious ways. I would suggest that 9 out of 10 is much closer than your 999 out of 1000. The condenser is a kind of capacitor and there has been a massive problem with cheap capacitors across many industries.
David "I can send you some if you like" Lieb
David Lieb

David the joke about capacitors and back axles is a joke however there are numerous posters on here that for a long time suggested the cure for every electrical problem was the condenser and that is the real joke.

I am responsible for many of our servers and client machines at work runing process control scada systems. We use Dell and I bet I can send you more cheap Dell fitted capacitors than you may have ever seen. This does not mean that auto motive condenser ar the same. In fact if I remember correctly there was with Dell motherboards a faulty batch thet had an X on the top where as good ones had a Y designation. At the time we investigated all our mother boards and any with X on the capacitors were sent back to Dell for repair.

If you want to spend an hour in the arhives then be our guest and locate as many genuine condensor problems as you can. If your estimate of 9 out of 0 is correct you should find hundreds. If I am right you may find one or 2!

Please ignore posts where the repair was conducted by changing everything at once except the spare wheel. LOL
Robert (Bob) Midget Turbo

Just noticed on my mg that the heat shield is mad out of cardboard and foil and is in a very sorry state so going to replace this and see if problem still occurs before I replace the condensor.
C Carter

If that doesn't fully cure it you could also look at the routing of your fuel supply (as suggested on another thread) to see if it's close to hot areas

but one step at a time - the heat sheilds are normally metal as far as I know
Nigel Atkins

Normally metal but this is stupid I will take a picture and upload it.
C Carter

I think my 1500 used an insulating material of some sort - a pseudo asbestos replacement. It could be described as a metallised sort of cardboard - quite fragile.
Guy

Sounds like the same thing yes it is more of an insulation type material.
C Carter

The fuel pipe running from the fuel pump goes across the back of the engine compartment to the carbs. It runs below the heater box and quite close to the back of the cylinder head. I think it can get overheated there, resulting in fuel vaporisation in the pipe and erratic cutting out when it is warm.
Guy

I there anyway to insulate the fuel pipe or would it have to be re routed?
C Carter

You can get a heatshield really easily, and, as I've said on other threads, before you fit it, cut the corner out so that you can still have easy access to the dipstick, otherwise you're always burning yourself ...!

As for the fuel pipe, no, you don't need to insulate it, but, if you get a longer one, then you can move it from over the engine, to along the innerwing side - ie, opposite - which keeps it alot cooler.

The other thing to think about is having some cooling holes on the outer wing - you can even just put 5 or so holes in - or a vent shape - let the air out.
rachmacb

I'd want to check the spark when it wouldn't start to rule out the ignition. I've had similar sounding problems with my sprite when it got hot, one time due to a bad year old coil and another due to quite new points wearing down quickly so there was virtually no gap. It would start fine but start to miss and stop when hot and wouldn't re-start until cooled for 1/2 hour or more with both problems.
David Billington

well just for a change I'm wrong about the 1500 heatsheild

thinking about it I don't think I've even seen under the bonnet of a 1500 for over 15+ years

Nigel Atkins

Hi all,

Another 1500 ('78) here with the same symptoms, I'm at a bit of a loss now, since so far I've:

Checked ignition - weak spark so new coil, plugs etc, I'm fairly sure I changed the points and condensor(!)

Replaced heat shield - the old one was crumbling away, and I felt that there was a good chance it was asbestos. Oddly, I don't recall this problem occurring before the shield was changed.

Pulled manifolds and re-faced, also replaced most of the studs - suspected air leak due to DPO missing off about half of the studs, and 'improvising' the rest.

Reset carbs, and balanced - several times.

I've just MOT'd (after a bunch of work, more on this some other time), and now want to drive!

I've a couple more thoughts on this, the behaviour is very like a stuck choke, but only happens when hot. The float bowls are full, but it's possible that they're too full, and effectivly flooding. Cooling down and normal evaporation would explain the restart after a while. This would point to holed floats (no obvious evidence of fuel inside the float), or stuck float valves.

The other thought is the waxstat jets - I seem to recall notes on this BBS about these giving trouble in the past, but can't remember details.

One last thought is that maybe the carbs are simply worn out and need a refurb - air leaking into the throttle bushings.

Any more ideas?

Cheers,

Sean
S W

Sean - last point first - air leaking into the carbs is a problem, but not the cause of this one :) The sooner you get that sorted, the less time you have to spend on balancing the carbs.

Have you checked the choke spring? They can (and do!) break, so that might have happened - and it's worth doing it, especially if you're getting other symptoms of that.

Do one (or two max) things at a time, that way you'll actually know what's happened.

What is it idling at?
rachmacb

Hi Rach,

I do need to check the bushings, but I seem to recall they were not too bad when this all started (carb cleaner test).

The choke returns are OK, the cam does get stuck occassionally, but it releases with a bit of a fiddle.

Idle when cold is steady at about 900, and very erratic when hot and cutting out.

I agree - change one things at a time, all the bits above were done bit-by-bit. Apart from sorting the manifolds that is. A large part of my history with this car (about seven years) has been correcting previous owners improvisations. I swear that they put the car together with whatever bolts etc were lying on the floor nearby!

Sean
S W

Don'tcha just love Previous Owners ...!!!!

You said that the problem started after the heatshield was fitted - did anything fall off or did you catch something accidently? Sorry for asking such a stupid question, but, we've all done something dumb :)

Mind you, my car throws a hissy fit everytime I change anything, she's a '78 too, so, it could just be that ;)

Suspect that the other high possible is the one that you've identified yourself - sorry.
rachmacb

Yup - I'll be starting a 'restoration' thread sometime soon, all those nasty little surprises will be revealed.

I don't think messed anything up when changing the shield, and everything has gone back in the way it's supposed to. It all had to come part again to do the manifolds too, so it got double checked.

I have had a few d'oh moments, usually when it's all back together, and I spot the bit that should've gone back on at an early stage. That tends to be the point where I step away for brew...

I think the plot for tomorrow is to prove the floats and valves, eliminate one thing at least.

It could be jealousy too - I've been running a BGT all winter...

Sean
S W

LMAO - there ya go - mine has gone into such a serious sulk I'm not even sure I'll manage to get her out for Midget50 after I got my BGT ...!!!!
rachmacb

And an update, of a long day (or so's) work and frustration...

I don't know if this will help any of the others with similar problems, but something may spark an idea. Apologies for some of the 'thinking aloud'.

I tried the engine between each bit of this, generally with no joy.

Checked the float bowls and valves. All seem OK, wiped all the rusty crud from the bowls, and flushed the caps through.

Fitted fuel filter between the pump and rear carb to prevent more crud and possible blocked jets.

Went back to first principles - checked plugs. 1&2 looked OK, 3&4 somewhat sooty, and a little oily around the threads.

Checked and adjusted valve clearances, mostly OK, tweaked a couple that were slightly too loose. Incidentally, I'm running on normal unleaded (not supermarket stuff), with no additives. Doing the same in the BGT, which is fine aside from being grumpy in the morning, and a bit of run-on after a good run.

Checked ignition timing - spot on at TDC, tweaked to about 10 degrees BTDC, engine instantly happier, but still cutting when warm.

Reset carbs to flat minus two turns, idle now erratic and too high, difficult to start too. Still sputtering and dropping when warm.

Rechecked all carb linkages, found the front choke operates at the same time as the fast idle cam, and before the choke on the rear carb starts to move. Reset.

Recharged battery, having been drained by all the cranking. Meanwhile, found that if starting from a portable battery, engine instantly stopped when the portable was disconnected.

(Time passes...)

Engine now really hard to start, will run for a few seconds then just stop. Definatly over fuelling, petrol seeping from float overflows. Some backfiring when throttle pressed.

Removed fuel filter in case it's messing with pressures, and reset carbs again to baseline - found that the jets were not returning to start position after choke use. Also found petrol leaking from the pipe at the bottom of the front carb, and from the jet assembly. Tightened pipe at the bowl, removed crud from jet body. Still leaking from the jet itself. Hmmm.

Engine now refusing to start altogether...

(getting desperate now...wait for everything to drain/evaporate, and for the battery to charge).

On a whim, checked condensor wiring, a bit grotty, so made up a new coil to condensor link.

Engine now starts, runs very lumpy, and can't seem to tune it at all. Still seeping from front carb jet. Checked voltage at battery with engine running. About 14.5v, maybe slightly too high, could be alternator, or high resistance battery (I suspect I need a new battery soon anyhow).

Research replacement carb costs, and resign to send them back to Burlen...

Order a reasonably cheap used set of HS4's from Welsh MG to get me going while mine are off for rebuild.

On another whim, before giving up, replaced condensor with the one that was on it seven odd years ago.

Engine fired up and runs fairly happily. I can't get a completely stable idle at anything like the revs needed, but it isn't too bad.

Ran up to temp, no sign of dropping, still a bit of a misfire. Tweaked carbs to minimise the misfire.

Went for a short drive in blistering heat and stop-start traffic. Got back OK with no drama (well, not from the engine anyway...)

So. The current state is that the carbs definatly need rebuilding, there's still a leak, probably due to simple wear. The linkage is sticky, and not quite right. Return to idle after running tends to drop the revs far enough to stop the engine, but the sputtering when hot seems to have gone. It's very difficult to set a stable idle speed, but it's reasonable at around 900rpm.

Was it the condensor, the carbs, the timing or the introduction of the filter? Unsure, but likely to be some unholy combination of several things.

Hopefully the spare carbs will be OK with a bit of a clean through, and will get me going until the current set come back 'as-new' from Burlen. This is on the 'list' for the forthcoming restoration, just wasn't planning on it right now.

For now, the battery is on charge to make sure it's full. I'm aiming to go for a longish run tommorow, to see what happens. And because I can!

Cheers,

Sean

S W

Well certainly isn't the condenser or the timing because the misfire is still there.

You have an horendous problem with the setting up of your carbs.

This statement says it all.

""Reset carbs to flat minus two turns, idle now erratic and too high, difficult to start too. Still sputtering and dropping when warm""

you seem to be not understanding how the idle works on the carbs. If the idle is high then there is only one way to cure it and that is with the idle screws, adjusting the jets to lower the idle is criminal all this does is enrichens the mixture to such an extent that the engine will slow and begin to stumble.

All the other info suggests that the carbs are a complete mess and for sure the balance will be a mile out which will account for changing idle and perhaps misfire at higher throttle openins.

Do yourself a favour and find some one local who can set the carbs up

here is another worry "Tweaked carbs to minimise the misfire" ??? simply set the carbs up correctly and move on I dont understand that statement?
Robert (Bob) Midget Turbo

Hi Robert,

I think I wasn't too clear, I'm not trying to set idle with the mixture; 'flat minus two turns' refers to the base setting of the mixture, as per Haynes, SU etc, not idle, which absolutely is only set by the idle screws.

I haven't been able to get the idle down to the specified 680rpm and stable with the screws. So far as I can tell by ear (and with a less than informative carbalancer) they're fairly well balanced.

I agree, the carbs are a mess, petrol dripping from the jet assembly onto the steering column is a bit of a clue, hence the decision to get some 'temporary' replacements, and send the current set off to Burlen for a proper rebuild (as part of a much larger project).

I'll freely admit to learning as I go, and will be getting both the temporaries and the rebuild properly set up - the first trick is getting the car running well enough to get to a pro.

(In case anyone's wondering, the BGT is the regular 'daily' car. I'm not even thinking of trying to tune that one (HIF's) myself!).

As to the last comment, very small adjustments to the mixture have made a difference to the slight misfire I was getting. No, I don't know why.

Sean
S W

what does this mean?

""Definatly over fuelling, petrol seeping from float overflows""

This means that the floats are not stopping fuel getting into carbs, thus impossible to set them up in this state

""Went back to first principles - checked plugs. 1&2 looked OK, 3&4 somewhat sooty, and a little oily around the threads""

This means one of the carbs is totally different to the other!!

""Reset carbs to flat minus two turns, idle now erratic and too high, difficult to start too. Still sputtering and dropping when warm""

This is simply a very basic starting point it is not basics it is from this point that you then set up the carbs. If you interpret haynes as saying anything else then I am afraid you have not understood it.

An engine has to have the following set correctly

Timing and carbs. These are not guesses and are not tweeks they are specific setting that when set correctly other items can be sorted.

As I have stated if you do not know how to set up the carbs then find help locally
Robert (Bob) Midget Turbo

And from your last post

""As to the last comment, very small adjustments to the mixture have made a difference to the slight misfire I was getting. No, I don't know why.""




Why? because the carbs are NOT set up correctly when they are then things will be far better.
Robert (Bob) Midget Turbo

I think we're sort of agreeing, though maybe not quite understanding...

As I understand things, the mixture is set by the level of the jet relative to the fuel level in the float bowl. The lower the jet, the higher the fuel ratio. The pump will send fuel until the float valve cuts the flow off, but there is an overflow which will send excess fuel out at the top of the bowl. This shouldn't normally happen, and indeed seems to have stopped (seems, because I haven't checked since the last run). Introducing a filter between the pump and carb may not have been a good move, as it could cause pressure changes, I've not put it back in s yet.

I'm aware that the 'flat minus two' is simply the starting point, not something to aim for. And yes, the difference between 1&2 and 3&4 plugs showed that the carb mixtures were way out - I noted that the front jet wasn't returning to it's base point after choke use. Wear and/or crud in the jet or sleeve, I think. This should be better now that I've gone from the base point and reset things to something near right.

Yes, engine timing is exact, 'tweaks' is probably the wrong word for small adjustments needed to get from 'spec' to actual, real world, settings to account for manufacturing tolerances, and 32 years of wear, tear, and previous muppets.

The simple fact that, idle speed aside, the engine is running smoothly and well, without cutting out, would suggest that I've got things fairly close, given the state of things. I think that there is enough wear in these carbs that it's not possible to set them perfectly, but they are set close enough to run reasonably well. I'll know better when I go back to it tomorrow.

Sean
S W

Sean,

Good to know that you have got it running better, even if not yet perfectly. Well done!

If you have fuel running out of the overflow pipe this only happens if the needle valves in the float chambers are not sealing properly. The result will be a high fuel level and make it impossible to set the jets correctly. The usual cause of valves not seating is either dirt in them, or a wear ridge on the conical face of the needle valve. Remove the float bowl lid, move the float down and take out the needle to clear any debris and check the condition.

I see that you know about Burlen as being the SU suppliers. Did you also know that they have download instructions for setting up the carbs on the web site? They are more detailed and specific than the information in the Haynes manual. I found the Burlen instructions better to follow.

Guy
Guy

This thread was discussed between 17/04/2011 and 23/04/2011

MG Midget and Sprite Technical index

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