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MG Midget and Sprite Technical - What do you think?

I bought my 59 Frog last year. It hadn't been MOT'd for several years so I overhauled brakes and a few other bits to get through MOT and made it to Gaydon. I think it still has the original gearbox and engine which has done 74,000 if speedo (which I think is also original) is right.
It starts well, idles well, but only gets up to about 50mph (40k rpm and oil pressure 60lb). Should I leave all alone or should I be expecting more out of the little darling. I have never messed about with an engine, other than ancillary bits like changing plugs, etc. and so not sure if I would know what I was doing if I took the head off.
Thanks for any opinions which will be greatly appreciated.
GrahamMV

I've been in a Mk11 Sprite with a 948cc engine (I think) and we were doing over 80mph (assuming the speedo was relatively accurate).
G Lazarus

Graham,
Checklist for you:
1. Valve lash. Rule of Nine is your friend.
2. Ignition timing. Preferably with a timing light so you can verify that the mechanical advance is working.
3. Pull the air cleaners off and rev the engine, verifying that both dashpots are opening smoothly together. Really sounds like is is running mostly on one carb, frequently caused by the other dashpot not opening properly.
4. Proper carb balancing and mixture adjustment.
David "even a 948 should be able to earn speeding tickets" Lieb
David Lieb

Gary's right. You should be easily able to get the speedo to suggest that you are doing 80. I would suspect that the car is actually going faster than 50, but that the speedo isn't recording correctly (though I notice that the tacho reading of 4000 would be about right for 50mph. Try to compare with a friend in a modern car, for starters. If this isn't the case, then start looking at the carbs. Are the butterflies opening fully? Or is something hindering them. Are they working together, or has the little linkage between them slipped so that one isn't moving with the other. Are the air filters clean, or need a wash out. Start with these, and see how you get on.

G
Gus Gander

Got Air !!!


I find having air in the tires makes the car run better,,,LOL

most likely just the condenser.

Prop
Prop***The End in 2012

40k rpm??? Should be a lot more than 80mph ;-)

Yeah, I assume you meant 4k rpm. IMHO that should be a lot more than 50mph. I would have thought closer to 65mph.
David "too bad everybody else's speedo is off -- so to speak" Lieb
David Lieb

At 40,000 RPM and an oil pressure reading of only 60 psi...., Id say its got to be the condenser without a doulbt.

Prop
Prop***The End in 2012

Thanks for the helpful posts. It certainly is not a problem with speedo, as everyone flies past me on the motorway!
I have not touched anything with regard to ignition and carbs. Does the fact that it starts without problem and idles smoothly give any clues? I am worried to seriously mess about with the carbs unless I have to, in case I get them out of balance, as I did that with an earlier car many years ago and got into a real mess!

I guess I should start with the easy stuff. Changing the condenser and cleaning the air filter. Can I just take the filter off for a short run to see if improves without it?

Eexcuse my ignorance but I don't know what "valve lash" is

Thanks for all your helpful advice
GrahamMV

valve lash = valve running clearances (tappets).
Once you've done the basics, treat it to a rolling road tuning session, if you are west mddx try Novatech in Slough, they are OK on carbs and did a good job on my racewr.
David Smith

An open circuit condensor will give easy starting but not allow engine revs to go high. Had that a few times in the 1960s when I was a Krypton techie.

Roly
Roly Alcock

Graham,
There will be lots of suggestions flying around. But my advice would be to try just one thing at a time. Then drive it again and see if you can detect any difference.

I suggest that the first thing is to check the points gap. They do gradually close down in use and probably go "out of adjustment" faster than anything else.

Guy
Guy Weller

Fraid he condensor is NOT going to be your problem, but what could it be.

If the speedo is accurate then naturally you ought to be able to get a little bit more out of it.

Without wanting to criticise someone with limited ability will not realise when a engine may not be firing correctly at higher revs. As David alluded to simple carb balance can result in the engines efusal to pull at higher revs. I had some one once who had problems with higher speed that was a simple fix of putting the same oil in both carburettor dampers.

You need to make sure the timing is no more than 32 degrees advanced at 4 thousand RPM (Vac disconnected) and that both carbs are exactly tuned the same. Find someone local who can help you with this, go to a local Car Club meeting where someone will be pleased to help you I am sure.
Robert (Bob) Midget Turbo

Easiest thing to check would be to pull off the air filters, start the car, and rev the engine while standing beside it. Shine a light down the throat of both carbs. You are looking for the sliding pistons to be opening in sync with each other AND thatabout the same amount of fuel can be seen spraying into each carb. If one of the sliding pistons (dashpots) is not opening right or if one side is not spraying as much fuel in as the other, you need to sort thatout. If you stop the engine and reach in there with your finger and lift the dashpot all the way up, it should slide back down into place with a nice click. I would strongly suggest you make these checks before adjusting ANYTHING.
David "trying to be helpful" Lieb
David Lieb

One simple thing to check first is the colour of the spark plugs.

If they are very black and sooty, you could be suffering from mis-adjusted carbs or clogged air filters.
Dave O'Neill 2

Yes, BUT, the spark plugs really only reflect what is happening RIGHT NOW. Looking at them after they have been idling nicely really doesn't give any meaningful data. OTOH, if you were to take the car out on the motorway and try to go as fast as you can, then turn the engine off, coast to the side of the road and pull the plugs, THEN you could get some interesting information.
David "not colour blind" Lieb
David Lieb

Graham where are you in Middx? I am in Ickenham with a 61 frog and I belived that I was the only frog in the pond!


j lloyd

Graham,

All the advice you have gotten so far looks good. But, I don't think anyone has yet said: NO! don't take the head off unless you first diagnose the engine to see if there is a reason to do so.

Assuming your speedo and tacho are correct, I thought 4000 rpm should get about 60 mph in a standard frog, so something does not look right with that. Is it possible that you have a slipping clutch?

Maybe j lloyd could come over and drive your car to give you his impression. By the looks of it, I'd say his is working properly.

Charley
C R Huff

There's so much helpful content here, I am really grateful to all of you. It certainly gives me a good idea of the areas to look at. Thanks a lot.

j lloyd - we are obviously quite near each other - I am in Northwood, in fact I came through Ickenham this afternoon in my frog!
GrahamMV

Im sorry graham,

The condensor suggestion is an inside joke on this board, I forgot to make mention of that.

I would not sweat the condensor un-less your replacing the points, and personally I wouldnt waste the money, Buy a pertronix chip or the Uk equivalent, you will get much better performance, and they are super easy to install, in less then 5 minutes

But as David says...start with the carbs 1st., then valves adjustment(google Rule of 9 for how to) then the ignition, then repeat the process agian to fine tune everything in.


If after all that and still no performance, you might want to look at a fresh cam on the next engine pull, those lobes can really wear over 30-45 years.

Keep us posted

Prop
Prop***The End in 2012

Thanks Prop. Didn't realise the joke; it seemed a nice easy fix. As you suggest, I will start on carburettor first (unless thats another joke!).
But as C Huff suggested, if j lloyd has the time, it would be good to hear what he thinks
GrahamMV

I wasn't joking. It really can be a symptom of an open circuit condensor/capacitor due to the coil not being able to recover in time beyond a certain rpm, in order to give a decent HT spark.

As stated previously, inspection of the spark plugs can reveal a great deal about the condition of engine and fuelling.

Roly
Roly Alcock

Graham, is your frog white and did I see you on the ricky road last year? I would be happy for you to try my frog out to compare your performance. I am around nxt weekend if thats any help? I am no mechanic but I know how they drive and how they are hard to stop!
j lloyd

Graham - you should be doing about 60mph at 4000, and the speedo could be out to that extent. But, does it just stop pulling at about 4000? I mean, if you keep your foot to the floor, is that it?

Frog engines are free-revving little things, and mine gets to 80mph without too much fuss.

So, what actually happens at 50mph?
Nick

Air filter on upside down can seriously impede performace... even tho' the engine runs smoothly. (It blcoks the carb vent hole on the front face...)

A
Anthony Cutler

Thanks. So I guess I should replace the condenser (will make Prop laugh if nothing else!), check the points, clean the air filter, and check out the carbs as best I can, and hopefully that will be it.

J Lloyd, it wasn't me; mine is green. Thanks, would be good to compare. Could you email me pls to arrange (gmv22@hotmail.co.uk)
GrahamMV

Well let me rephrase a little bit,

The Condensor could be an issue, but more as an out of adjustment situation, rather then a failure of the condensor, if the condensor were bad or going bad it wouldnt start or would die soon after starting.

The Joke is this...Because the condensor is made in china by 6 year old little girls working 16 hour days, they go out vary freqently and when you buy one, you buy 5 at a time, and hope at least 1 is good.
So they are a real problem, the easy fix is a chip that replaces the points and condensor as I mentioned before. So when someone mentions "my transmission wont shift" or "my brake caliper is leaking", or " I got a wierd sound from the rear boot". We blame the problem it on the condensor.

As to the ignition, I REALLY have to recommened using the chip instead of the old points and condensor...its only $100 USA, but you install it in under 5 minutes and forget it, never adjust agian, Also it evens out the idle and other problems caused from wornout wobble Dissys...BUT do remember to re-lube the inside of the dissy every 12,000 miles or once a year...unless your car is concourase The chip is Definatly, the way to go. In fact I would install the chip before Id did anything with the carbs



Prop
Prop***The End in 2012

In the states, this is a popular choice for chips that replace points and condensors with, you have the same chip in the UK also just under a diferant name..cant remember it sorry.

http://www.pertronix.com/prod/ig/ignitor/default.aspx

prop
Prop***The End in 2012

I thought the condenser joke was because it is always blamed for everything first time and yet to date in the last 10 years on this board it has never been the problem!
Maybe I didn't understand the joke?
Robert (Bob) Midget Turbo

4k rpm and only 50 mph. Couldn't be a clutch slippery thing?
Rolf

Bobert,
It has indeed been the problem at least once, in the case of Gryf's dissy. I imagine a few others will chime in as well.
David "it still makes a good scapegoat" Lieb
David Lieb

Interesting what you say about the chip, and I guess you are right. But I need to get my head round it, as there's a little voice telling me its not authentic. Is there a way I can test my existing condensor? Is it a case of just putting a meter across it to check there's no continuity?
GrahamMV

you can put a charge on it, then convince the wife to pick it up, if her hair catches fire its okay


Prop
Prop***The End in 2012

Hey David,

What was that line you came up with about a year ago...

****A good working carb fixs a broken ignition, a good ignition solves a poor carberation******(something like that.)

how did that go, I cant remember, but I always liked how you phrased that little diddy bit of info

prop
Prop***The End in 2012

Prop,
The classic quote (lamentably not mine) is that 90% of all carburetion problems are caused by the ignition and 90% of all ignition problems can be traced back to the carbs."

Graham,
I do not believe that the usual mechanic has the means to conclusively test the condensor other than by replacing it with a known good one. Please note that I did NOT say a "new" one. "Made in India" or "Made in China" or any number of similar terms equate to "may be dead right out of the box".
David "optimist with a glass twice as big as required" Lieb
David Lieb

Thats it!! Thanks, I got to write that down somewhere.

"90% of all carburetion problems are caused by the ignition and 90% of all ignition problems can be traced back to the carbs"

Dead out of the box!!!! I can attest to that, when I had the loom fire 2 years ago, I went back to points and condenser for a short time, and took 3 "NEW" condensors before I found one that worked


Prop
Prop***The End in 2012

When the Triumph TR5 was launched and I was an apprentice at a Standard Triumph dealer, there were loads of finger pointing at the new fangled fuel injection system every time there was some poor running or bad starting. David's 90% rule applied equally well back then. Nearly every single problem was caused by the ignition component failure or incorrect ignition adjustment. (no problems caused by condensor fail here....)

The injection system problems came along some time later when wear had taken place.

Roly
Roly Alcock

OK, I get the picture. I was hoping it was a small ignition problem so I guess it's 90% certainty its the carbs. So I will start on the carbs instead, which I guess gives me a 90% chance its the ignition ............
GrahamMV

I still suggest you check the points gap first. It is simple to do and there is no doubt about it - the setting is either right or wrong.
Guy Weller

seconded!

I'd say the chances of it being a "lectrickery fault" are even greater than using David's rule

almost all of my experiences as a Nay Aye man showed this up as fact

A working carb usually stays working

working 'lectricks often pack in...

(and if it IS a carb fault it is often very easy to spot, loose screws and suchlike, dirt blocking air into emulsion tubes and other vents and jets...)
Bill

Bill,
I agree, That is why I suggested that he take a quick look at the carbs (NOT adjusting ANYTHING). If the dashpots are moving in unison and dropping freely with fuel coming through both carbs, it should be ignition.

Guy,
Last time I did points, there was a wide range of settings possible for the gap. Tweren't black and white by any means.

BTW, I think the strangest carb fault I have had was when I was up until 2ayem trying to get the car to run a little better prior to a 1500 mile trip and did not do a very good job on the linkages. A couple hundred miles from home I mashed the fun pedal and one of the lever pins jumped out of the throttle fork. OPne carb now was unable to return to the idle position and the other carb was not being moved at all. The car idled at 3000rpm but could not reach 50mph. Fortunately, the fix was easy once I popped the bonnet and looked...
David "then there was the time..." Lieb
David Lieb

I'll give it a third, and raise you a "sort the electrics and adjust the valves before you start on the carbs".

Charley
C R Huff


graham

if you're not sure what's causing the problem, why not get a decent home tuner out to look at it, the diagnostics on these machines are fantastic, don't remove the cylinder head unless there's a definite reason to, blown head gasket causing overheating or water contaminating oil or vice versa or other associated symptoms.
it's always best to start with the easiest possible causes first then start looking at the more major possiblities rather than the other way around...

john.
j b biggs

hey graham,


Do you have a haynes manual, If not that would be a great place to start, But Id certianly take the car by one of the midget pubs, Try starting another thread asking " where Do Mg guys meet up on a weekly basis at the local water hole", and meet up with some of them, I think there are several in the middlesex area, they could sure give you some insight...(or give you a ride home when they blow it up...LOL.

But ALL the above is great advice.

Hang in there ...its a midget after all

Prop
Prop***The End in 2012

With faults I always think about how the symptoms occurred.
An instant change in performance would mean that something had happened suddenly. Maybe broken (throttle cable) stuck (float needle valve) fallen off (plug lead) or run out (petrol).
There are the gradual changes to an engine that hasn't otherwise been touched, and these would be down to things that wear or go steadily out of adjustment. Points, sticking throttle slides, dirty air filter, and other electrics like failing HT leads, worn rotor arm and even condenser.
There are the long term gradual change items like valve clearances and timing, but in reality these do not generally alter much unless you have done other work on the engine.
Graham's description sound to me like one of the gradual change items. From those I would start with electrics, and especially things that can be visually checked like the points and yes, then the throttle slides.

Guy
And Mr Lieb, there IS a correct setting for the points. Yes the car will start and run if the gap is too wide or too tight, but it will only run properly when they are set at 12 thou. Apart from effecting the spark strength, having the wrong gap also effects the timing.

Guy Weller

Mr Weller ;-)
I am aware of the correct setting for the points (one matchbook cover, right?). I am also aware that they can be within a fairly significant range and still work just fine. I was taking issue with the concept of "the setting is either right or wrong". If you are using actual points, the setting is gradually changing as the block wears anyway. Yes, it is affecting the spark and the timing. However, if the timing was set currectly at the current gap, fixing the gap will adversely affect (not effect) the timing. Likewise, the effective gap is difficult to read correctly on a set of used points unless you are using a dwell meter, since the surfaces are no longer as flat and parallel as the factory might have intended, even with the judicious use of a points file.

Nonetheless, if it were my car, I would start by observing the carb action, checking the distribuor settings, taking a compression reading, then posting the results back on this forum and pleading for advice again ;-)
David "P.O.E.M" Lieb
David Lieb

All good advice David.
I would however think it reasonable to assume that when the timing was last checked the points were accurately and correctly (not currectly) set. Thus, if the heel of the cam follower has since worn, then the points gap, and consequently the timing, will be wrong.

But I do not disagree that the carbs should also be checked. And then of course, there could always be more than one fault! ;-)
Guy Weller

Well I really appreciate all the comments and dont want any of you guys to fall out over my car!
All the advice is good. Prop-I have the Haynes Bible, and in fact it says the points gap should be 0.014 to 0.016 in (.35 to .40mm) but Guy's post is suggesting .012. Any views?
I suppose I should really invest in a new set of points unless I splash out and go for the Ignitor that Prop is suggesting.
As soon as I get a chance to get my head under the bonnet, I have plenty of ideas what to look for, so thanks v much.
What I have really learned from this thread is what a helpful bunch of people in this community. J Lloyd has kindly offered to meet up and we can compare notes. Regards
GrahamMV

Oh so true! What is the saying? Something like, "Just because you have found 'A' fault does not mean you have found 'ALL' the faults."

Ideally, the Wiki would have a diagnostic flowchart that would render a list of things to check and report back on before adjusting anything.
David "among other mistakes I have made..." Lieb
David Lieb

Graham,
Not to worry; none of us are going to come to blows over this. We all have our pet theories based on our own experiences and are willing to defend them with virtual blows, but we are all still friends and virtual blows leave few scars or bruises. "Bench mechanics", so to speak, as opposed to "bench racing". If we float enough theories, one or more of us is usually right in the end and the rest of us hoist a virtual brew in their direction.
David "not my turn this time" Lieb
David Lieb

graham,
I'd get it running properly on points first before going for the electronic trickery. I've fitted an ignitor and so far its been fine but I had a fair bit of trouble on first fitting due to my own stupidity and at least I could be sure that the problem was either with my installation or the ignitor itself as the car was running fine on pints until I pulled them out! i.e. only introduce one variable at a time!
I'd follow the good advice above. Check the points then run it roound the block, check the timing, run it round the block, check the carbs etc. etc. Sooner or later you will find the problem and then follow Haynes to make the necessary adjustments. Even an idiot like me can just about get the timing and carb tune right with no more than a spanner a screwdriver and a lot of patience!
Matt 1275 Bucks

David,

One matchbook cover to gap the points might be OK in the States, but over here matches usually come in boxes and a box of Swan Vestas may be overkill. :o)

Just getting away from the thread a little - my dad had a boat powered by a 6hp Kelvin paraffin engine of 1920s vintage. In the handbook it stated that "the valve clearances should be adjusted to the thickness of a visiting card"

Precision engineering in those days.

Dave
Penwithian

Nobody has yet mentioned that it's dwell angle that should be correct rather than the points gap which is a means to getting the dwell angle set correctly [degrees of rotation while points are closed] (60 degrees for early distributors).

Good thread this. Itching to find out what the actual problem turns out to be.

Roly

Roly Alcock

Graham


Haynes is right at 0.014 to 0.016 in.

Guy was probably thinking of tappet clearance.
Dave O'Neill 2

Roly,
Do you not read the posts? I already mentioned that "... the effective gap is difficult to read correctly on a set of used points unless you are using a dwell meter..."
Tsk tsk tsk ;-)

Perhaps .012 is the correct gap for a set of used points...
David "Roly's itch is contagious ;-)" Lieb
David Lieb

if we're throwing dwell into the equation I prefer to set Lucas dizzies at 55º as a general rule.
Bill

No, Dave is correct - I was mistaken and clearly thinking of the standard valve clearance. Sorry, brain fade!
Actually it is a long time since I checked points as mine now has an electronic dizzy from an MG Metro. And when I did last check points it was with a dwell metre, but I was trying to keep things simple. Graham had implied a limited knowledge and toolkit. Part of the reason I wasn't suggesting using dwell angles.
Guy Weller

:->
Bill

Do ye mean to tell me the Brits canna spell "meter" either? ;-)
David "I can spell 'Prop'" Lieb
David Lieb

We have both sorts. As with gaps, I chose the wrong wrong meter (metre) !! ;o}
Guy Weller

Guy's absolutely right. I have very limited knowledge and toolkit and have absolutely no idea what dwell angle is (I'll do my homework, promise). But presently itching to find the time to get my head under the bonnet.
But I do have one final question please. As I said at beginning, the car starts very well and idling is excellent, only real problem is speed at top end. Would this imply problem is vacuum advance? Excuse my ignorance if thats a daft suggestion.
GrahamMV

Sorry, Graham, but it is unlikely to help. It could be in the mechanical advance..
David "not making any advances" Lieb
David Lieb

Maybe we are all in the wrong box!
Are you sure that your brakes aren't binding a bit?

Easy way to tell is to go for a short drive on quiet roads, using the brakes as little as possible. Then stop and feel if the drums (and discs ?) are hot. Rear drums should be pretty well cold. Discs - if yours has them - may be warmish but not hot. A slight drag on the brakes can certainly knock 10 or 20 off your top speed.

Guy
Guy Weller

Interesting suggestion. I will try that out when the roads dry out. Dont want to get her wet!
GrahamMV

Took it for a 10 minute drive, the brakes still ice cold. Good suggestion but sadly not the answer. I haven't checked points yet - I know its very easy but have had problem with my hand and it will have to wait for time being. Report back in a week or so, hopefully.
GrahamMV

Graham.
Nobody so far has suggested to check the total throttle opening when the engine is off. It could be that the linkage is not allowing full throttle.
Sandy
conrad sanders

Thanks Conrad. Yet another helpful suggestion. As soon as I am better I will have a look.
GrahamMV

This thread was discussed between 24/01/2009 and 30/01/2009

MG Midget and Sprite Technical index

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