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MG MG Y Type - Mis-behaving YA

Having taken ownership of my first Y (and first classic car) towards the end of the 2010 "season" my use of the car was, until last weekend, limited to a few short trips. Over the winter, work on the car was limited to minor fettling with the only under-bonnet (hood) work restricted to replacing water hoses.
However, I have just returned from my first "run", the Anglia Centre's excellent Mid-Summer event from Needham Market in Suffolk to East Ruston in Norfolk. Including my journey to the start and return at the end I knocked up some 250 miles in the three days. Not a lot for many experienced owners, but for a novice Y driver it was a wonderful experience and a real booster of confidence in my car. Better still, my wife also thoroughly enjoyed the run and the social contact with other MG owners. (I now call her "navigator" - but she still refuses to call me "Captain"!!!)
The run was not however, totally trouble free and I would be grateful for any advice or suggestions or comments that might help cure the problem described below.
On what at first appeared to be totally irregular and apparantly random intervals the engine would suddenly start to run rough and lose power with much juddering and jolting. These were not frequent occurances and indeed we could run for an hour or more without any sign of a problem. When the fault did appear it rarely lasted more than 20 seconds and then it would clear and all would be back to normal. Taking the engine off load by dipping the clutch allowed the engine to run smoothly and it could be revved with no difficulty. I took no remedial action at the time but let the car work through its hissy fits and then carried on preferring to leave well enough alone. However, now that we are back home I want to try and get the fault sorted.
After about six occurrences I thought that the fault might be occurring after "high g" manoeuvers around roundabouts or tight bends but this might be a red herring. As a result I was tempted to think it might be fuel related; I am going to check tomorrow, but I don't think there are any after-market filters fitted. The only other information I can think to mention is that it occurred before and after fuel fill-ups (unleaded) from two separate and reputable sources. I am tempted to draw (perhaps jump) to the conclusion that if it is fuel contamination could it be internall generated? If so what would be the recommended solution? The car has a cylinder head modified for unleaded fuel.

On the other hand - I guess it could be electrics!!!!
All contributions gratefully received.
Don Avery
D G Avery

Hi Don

Glad you had a great time. It is always nerve wracking though when something happens you cannot quite put your finger on.

My immediate guess is fuel related. Electics tend less to come and go. So with the fuel, the most imporatnt part is as far as the engine is concerned, a good even flow at least equalling the demands put on it. So this is what is known as fuel starvation. There are two kinds - a blockage in the line that is not allowing enough through like a piece of dirt in the bottom of the float bowl or more probably vaporization.

So here is a question: did you have nice placidly warm mild to good temperatures for your drive as you havent really told us much about how beautiul a day it was in your part of the world?

So now you are thinking where is he going with this and why is he now moving onto this topic?

Open the right hand side of the bonnet/hood on a standard Y and study the way that lovely copper fuel pipe comes gracefully up and over the firewall/rear of the engine compartment, up into the SU Fuel pump mounted on the side of the battery box then outputs down the flexible hose under that big old aluminum air intake. Take a while to think they nevermissed an opportunity to stick that logo anywhere they could. Then up pops the pipe to the top of the float bowl. Isnt it a clever way that cut off valve works, beautiful in simplicity so as not to overfill the float bowl, then that powerful engine just sucks the right tiny amount through the carburettor and on into that intracte one piece casting inlet/exhaust valve.

OK now look at it again and start where you did before and as you follow through think you are a high vapor liquid passing through all these nice warm areas on a hot day and,oh yes, there is a flaming hot exhaust pipe down there too. As a last gasp you pass into that hot inlet manifold you are sweating like a pig and sometimes there just isnt enough puff left as you get into the nice warm clyinder to be burned to death by the spark plug - you died a couple of feet up the process!

Well that is pretty close to understanding how our engines are on a hot day.

So, here is the $64000 question - do you have a heat exchanger? Modern E15 unleaded fuels burn hotter than the garbage our XPAGs were built to cope with, so my suggestion is to go to http://www.mgccyregister.com/node/32 and scroll down and you are looking for Y Sheet 1 – Steering Column Electrics by Jack Murray priced £3.00 plus S&H. Get a copy of that and in the back Jack shows a design of a neat heat exhanger/shield he made. I had one of my shop people make me one up and he used a slightly heavier guage of aluminum than Jack specifies but it does make that much difference (heavier just means higher heat transfer capcity) and I also fitted one of the isolation blocks from the MG SPRIGET range as suggested too.

It is a very elegant solution to the problem.

Time for a pain killer now, so hope you didnt mind me doing this the entertaining way.

happY MototinG

Paul
Paul Barrow

I had (maybe still have) a similar problem with my YB. It ran very well most of the time, but occasionally developed the spluttering that you mentioned. On my car, it only occurred during very hot weather when the engine was really hot. Dipping the clutch and revving the engine cleared the problem. I also had the vapourisation problem that Paul describes. If I switched off when the engine was very hot, it would not re-start until it had cooled down.

I fitted a heat shield to Jack Murray's drawing with insulating spacers on each side. I used 5mm thick spacers, available from SU Carburetters for a few pounds each. (Google SU Carburetters and you will find the site.) You can order online. The spacers were hard to find on the website - the part number is 134936. I overhauled my carburetter while it was off and fitted new seals, jet and needle. I used the DZ needle as recommended for modern fuel in the Y Type. I also insulated the copper pipe above the engine using material bought on ebay.

I made up the heat shield myself without any difficulty using an offcut of 1.8mm thick stainless steel sheet bought for a few pounds from a local steel fabricator. The only special tool that you need is a 29mm holesaw, which cuts a hole of exactly the right diameter for the blocks. Other than that, you just need a hacksaw, file and a drill.

Stainless steel is harder to work than aluminium, but it is also much heavier and has the advantages that Paul mentioned. I used this because I saw an advert for a proprietary shield for a TD, which explained the benefits of stainless steel. It certainly looks good on the car.

I then painted the exhaust manifold using silver extreme temperature paint (£15 from Holden Vintage and Classic Supplies.) I remember from schoolboy physics that light bodies radiate less heat.

After doing all of that, I still had problems starting a hot engine. I asked for help on this BBS and got a lot of advice. So far, I have replaced the condenser in the distributor (you can get a new one from the MG Octagon Car Club or any of the other usual outlets, although I find the MGOCC generally cheaper, especially if you are a member) and advanced the ignition timing to about 2.5 deg btdc.

This has certainly improved starting generally and the car seems to run more smoothly. Unfortunately, the weather here (Isle of Wight) has been abysmal since I did this, so I have not really had the chance to test its effectiveness.

I also bought a new coil (MGOCC again) as someone suggested that an old coil can be problematic when it gets hot. I have not fitted it yet as I want to see what effect the new condenser has first. It is always useful to have a spare coil - you never know!

Mike

M Long

Paul describes fuel starvation by vapourlock, caused by boiling petrol in the floatbowl and fuel lines.

Another cause for fuel starvation can be clogged fuel filters inside the pump. Especially because it happened before and after filling up. With a near empty tank the accumulated crud gets mixed with the smaaler amount of fuel, resulting in a higher "fuel/crud ratio". The flow of fresh fuel through the crud would result in a uniformly fuel/crud ratio throughout the tank.
If the filter in the pump is indeed clogged, it would be prudent to clean out/flush the tank.

You can also check the condition and adjustment of the contactpoints in the fuelpump.
Willem vd Veer

Paul, Mike & Willem,

Thank you all for your helpful inputs, all of which I have taken on board.

Firstly, it was remiss of me not to give a met report for our weekend run as I should have realised that it could be significant to the diagnosis of the problem. I was aware of the problem of fuel vaporisation but at the time I discounted this diagnosis for three reasons:
1) the weather was relatively cool throughout the weekend.
2) I perhaps wrongly assumed that to recover from a fuel vaporisation event the car(or perhaps more accurately the carb) would need to cool (or be cooled). During my periods of rough running I kept moving and after a very short period the engine would return to normal running.
3) My car appears to already have some form of heat shield fitted although it does not appear to have any spacers fitted as described in Jack's Y Sheet No 2. Furthermore, I have not positively identified the material but it has been painted silver!

In an attempt to do something more positive I decided therefore to start with Willem's second suggestion and check as far as I could for signs of crud in the fuel. After leaving the car standing and un-used for a couple of days I opened the float-chamber and removed the float to find a significant deposit of very fine brown powder (about the consistency of talcum powder). I would guess that it would result in a fairly high crud/fuel ratio when stirred up in the contents of the bowl! In the process of checking the state of the float-chamber I also noted that the filter has a small but significant hole in it.

I have now cleaned out all the deposits, ordered a new gasket kit and filter and will also try to get a new filter for the pump whilst I am at it. I am also considering installing an after-market in-line filter which I understand should be fitted on the output side of the pump.

In the longer term (over winter) I guess I will need to investigate the state of the fuel tank to try and establish the source of the crud. I will also look at upgrading my heat shield.

Thanks again for all your inputs and Paul, I wish you a speedy recovery.

Don


D G Avery

Don

I would put the inline before the pump personally to give the pump filter half a chance. These can be fitted to the pipe under the car as it runs along the chassis rails for relative hidden installation and also fairly easy replacement but that will be up to you.

When you are ready to do the tank buy your seal kit direct from Bill Hirsch - Moss sell the same kit so yes you will pay more in shipping from Bill direct to the UK but my guess is that your total bill will be lower.

Bill's kit is first class and I have used it with great results in every case.

Paul
Paul Barrow

Paul,

Thank you for the pointer to the Bill Hirsch site. There is some very useful and interesting stuff there.
On the fitment of the filter before the pump can I draw your attention to Dave DuBois' article "SU Pumps Facts and Myths"
http://homepages.donobi.net/sufuelpumps/Fuel_Pumps/SU_Fuel_Pumps_Facts_and_Myths.pdf
which specifically discourages the fitting of filters on the input side of the pump. It was this paper that prompted me to make the comment in my previous post.

As an aside - what an excellent source of information Dave's site is on all things SU.

Don
D G Avery

Hi Don

Yes I met David before we moved here and he, and his wonderful wife are 85 mile up the road from us. We see them quite a lot.

I agree with David as far as the dirt collection issue goes and the ability of the Y fuel pump to shift stuff is legendary.

So long as you are checking and replacing it frequently and not forgetting it then either place is fine. If you are a forgetfull person then he has a point. At least putting it before does prove where you are getting the junk from though and is easy to patch back after you drop having one.

What Dave (or Russ as he is also known) does not know about SU fuel pumps isnt worth knowing so his website is a good resource too. Glad you like Bill Hirsch too, he is another good guy I have done business with for a long while and I have sucessfully reconditioned a good number of tanks with his stuff too.

Paul
Paul Barrow

@ Mike,

Now that I read your post again on a Friday-afternoon at work I have some comments/questions (in a Friday-afternoon manner).

In which advert did you read that a stainless steel shield is better? I chose aluminum for it's better heat conducting properties compared to stainless steel, trusting it would also act as a cooling fan to the carburettor foot. Not having a sheet of stainless steel laying around when I wanted a heat shield, may have had an influence, too.

You say: "I remember from schoolboy physics that light bodies radiate less heat". Either you weren't listening or your teacher was not up to date ;-). Painted surfaces radiate the same heat regardless of the colour. More worringly UNpainted surfaces radiate less heat than painted surfaces, if you want to delve into this, read attached article:
http://books.google.nl/books?id=L4jtv2mX0iQC&pg=PA137&lpg=PA137&dq=painted+surface+radiate+more+heat&source=bl&ots=h9bayk4eY3&sig=hN0bQHIR5qGlM4BL_6xsJvhSYVQ&hl=en&ei=A6wEToPND8joOaWQuM4N&sa=X&oi=book_result&ct=result&resnum=4&ved=0CC8Q6AEwAw#v=onepage&q=painted%20surface%20radiate%20more%20heat&f=false
Willem vd Veer

I may be out of date in many ways - I was born shortly after Y Type production started - but I remember Kirchoff's Law of Thermal Radiation, which in simple terms, states that a poor reflector is a good emitter, and a good reflector is a poor emitter. It is why, for example, lightweight emergency thermal blankets are based on reflective metallic coatings: they lose little heat by radiation. This may or may not mean that my silver painted exhaust manifold radiates less heat than it did when it was rust brown in colour. However, it looks an awful lot better now!

As far as the thermal conductivity is concerned, surely it is better if the heat shield material has low conductivity. I have fitted an insulating spacer on both sides of the heat shield to minimise the heat transfer from the manifold to the carburetter by conduction. Another advantage of stainless steel over unanodised aluminium is the reduced surface corrosion, which means that it will not lose its surface lustre. I used an offcut piece of brushed stainless steel, bought from a local fabricator for a few pounds.

I am well pleased with the result and I think it was worth the extra effort in cutting and bending.
M Long

This thread was discussed between 20/06/2011 and 26/06/2011

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