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MG MG Y Type - Starting Problems

Y4002 is playing silly B******, she won't start when hot. Cold starting is satisfactory, and she runs like a dream even when very hot, no sign of misfire etc. Normal temperature on the temp guage with sensor in the radiator is 170 F and never goes above 190 even when pulling hard up a long steep hill. But, pull up at a filling station, try to restart, no chance, until the temperature drops below 150. Many times I have dismantled carb and ignition system on the forecourt without identifying the problem. Now I just open the Thermos, pour a cup of coffee and wait about 45 min. before proceeding.

When playing up, there is fuel to the carburetor, a healthy spark at the plugs and good compression, when checked, the plugs are dry. There is no obvious reason why! I thought about vaporisation, so there is a nice polished stainless steel heat shield with insulating blocks either side keeping the carb cool (and it works!)
The ignition system has been rebuilt with new leads, plugs, points and coil, the distributor I rebuilt about 3000 miles ago when the problem first arose. (co-incedent with the arrival of E5 fuel) The problem seems to be worse when using supermaket fuel and was dreadful when I inadvertantly fueled with Super premium. so I avoid those now!
The head has been converted to unleaded
Still the same old thing.

Any suggestions any one?

Regards
Dave
D P Jones

Dave

Presumably you have no heat shield fitted?

I would suggest firstly getting a phlonic insulation/stand off block as fitted to the MG Midget/Austin Healey Sprite (same size as the MG Y back of the carburettor) and 3 new gaskets and some slightly longer bolts (get these when you know how long you need them to be after you get the block) and fit that first off. This will give you a little better heat insulation to prevent HOT SPOTTING. The real cure is to get a proper heat shield made. There are some excellent plans in the MG Car Club Y Type Register Data Sheet 1 - fitting a heat shield to the MG Y. I had mine made to this plan out of slightly heavier gauge aluminum than suggested and it, together with the block, work perfectly.

Paul
Paul Barrow

Dave,
Next time if you stop the car for less than 20 minutes, open the right side of the bonnet as soon as you stop.

When ready to go, close the bonnet and see how it starts.

I think your problem is part radiant heat & part heat sink, and part modern fuel - it vapourises at 70 degrees celius !. So once any part of the fuel pipes, pump or float bowl exceed 70 - poof - the fuel disappears.

I use the 20 minute rule all the time, and it works - especially in summer in Australia !.

cheers

Octagonally Y-Typing

Tony
A L SLATTERY

Hello Paul, I have fitted a polished stainless steel heat shield with insulating blocks either side which keeps the carb cooler than before, as indicated in my post.

Hello Tony, the idea of opening the bonnet side and waiting sounds a good idea, providing I don't stall the engine trying to escape from a side road during heavy traffic!!!

Happy MotorinG

Dave
D P Jones

Hi Dave,
Are you running on genuine old original points or modern replacements?
Have you checked the gap immediately it refuses to start when hot?
Keith D Herkes

Hi David

How are you getting on with your 'overheating' problem.

Having witnessed your problem first hand last Saturday at Bwlchygroes I was sruck by how quickly your Y began
playing up, we were only in the 'parade' about 15min and although you have only one fan blade (try and get another one!) I would not think you should have reached a problem temperature in that time.

So either your Y overheats very quickly or is very sensitve to temperature or both! (sorry to state the obvious but it sometimes helps)

The temperatues you mention seem reasonable ie 170 & 190 however these are at the radiator and depending what happens between engine and radiator may indicate a higher engine temperatue worth checking!

Coils can be heat sensitive and although you have changed it, may be worth trying another one hung in during a warm up!

I think the E5 just tipped your car over the edge, you obviously have an underlying problem! You saw my TC no heat shield no insulators no problem!

Let us know how you get on, if you are still stuck come over to Bronwydd, I have some spare coils etc.
or just to see Demelza the YB( previous owners name)
and a cup of coffee.

Best regards
Brian


b r hough

I suspect coil breakdown has a lot to do with it too now that you mention it Brian. Had a very similar situation with mg Magnette and it was indeed the coil, I would say Dave, throw a new coil on - they arent that expensive.

And yes, if you only have one blade (I presume you actually have one that goes either side of the water pump aka 2 blades but one piece) then absolutely yes, get another soon! Go easy on getting the studs out of the water pump as they snap easily and then you will be stuck having to take the radiator out (not a nice job).

Paul
Paul Barrow

Dave

My YB suffers from the same problem, despite having a heat shield and insulating blocks fitted. I was getting used to standing by the roadside for 20-30 minutes while the thing cooled, trying to ignore the acid comments from my other half, and waving away offers of help from other motorists.

I have found that pulling the choke out while turning the starter works. I am not sure why, but the problem is caused by a vapour lock in the carburetter - a consequence of modern petrol with all of its 'improvements'. Pulling out the choke causes liquid petrol to be drawn into the hot engine, which vaporises in the cylinders rather than in the carb.

It is worth a try.

Mike
M Long

I have in the past used a small hand water spray over the petrol pump to clear a petrol vapour lock, I would think it could help for the carb, if that is the problem. However since the modern fuels burn hotter it could be that when hot some of the valves may not close completely. The valve clearances of 19 or 12 thou was advised before hot fuel was available. If this is the problem as it was on my 1250 TF and Ford Anglia easing the valve clearances by 1 thou should do the trick. Bryan
B Mellem

I don't want to crow too soon, but I think the problem is now solved! thanks to the collective wise council on this thread, the moral support and practical help from other Y typers, (thanks Brian). Of course it was the coil! We gave it quite a stern test today on the Pendine Dash, over 100 miles through the white lanes of Pembrokeshire some pretty steep hills and frequent sight seeing stops - and a prompt restart every time!

(A very well worth while run, we need more "square riggers" so come on Y typers give it a go you know you'll enjoy it)

I temporaraly popped a brand new modern (Morris 1000) coil (2 actually, first one had to be sent back as duff) and in doing so needed to confim the connections, marked + & - not CB and SW I found an interesting MGA site that quickly dispelled a 40+ year firm held belief that CB must always go to the contact breaker. Coils are polarity sensitive because they need to provide a spark from the plug tip to the plug body, not the other way round. (The CB terminal is common to both HT and LT coils as is the + terminal) (SW & - are connected to the LT coil only)

I had, in the past, changed the car polarity from +ve to -ve earth, thus the coil was connected the wrong way round. So the new coil was connected + to SW and - to CB. When I tested this setup with an oscilloscope, spark was going in the right direction, but about 10% down compared to the opposite polarity.
When I tested the car on my favourite test hill performance was down with the coil the "right" (+ to CB) way as compared to the finalised way (+ to SW) and today, running east from Haverforwest on th A40 on the long steep hill with 2 passengers, she flew up the incline, passing two moderns on the way!!
This has been an interesting exercise, petrol feed pipe re-routed along radiator stay, stainless heatshield and tufnol insulating blocks, new petrol pump,carburettor rebuilt and correctly set up, all ignition components replaced, distributor re-built, timing re-set. Finally, replacing and correctly connecting the coil.

I now need to find a suitable original type coil, suitable for -ve earth, (don't want to revert to +ve as I have put a transistor in the clock) The Original (1949 dated) coil performs correctly on the bench and when stuck at the roadside, so not convinced that there it is faulty and I'll try it again but now connected correctly!

The 2 bladed fan doesn't seem to be an issue in this context, the radiator temperature was maintained at a stable 160-180F even when waiting for "grockles" to discover they had a reverse gear after all when confronted by a Y following a pack a RV8 MGB etc. It could be a problem with balance though which might impact on the water pump, but so far over the last 40 years it seems to have been O.K. so I'm on the look out for the other blade, or would an electric fan be better? ah, but that's another thread!
Regards and thanks for all your help. (apologies for the long missive, but I thought I owed an explanation.)
David

D P Jones

Thumbing through my W E Blower manual there is a referance [page 440]that in the case of a very modest change in tunning 8.6 compression that when using a blend of petrol and benzole the tappet clearance should be 22 thou, One can only assume that valve expansion with the addition of benzole was already a problem then and every time the head is re-surfaced the compression will slightly increase. Bryan
B Mellem

This thread was discussed between 30/07/2012 and 16/08/2012

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