Morris Minor Owners Club

1275 mg midget engine
I have fitted a 1275 midget engine with a 3 branch exhaust manifold mg metro inlet manifold and hs4 su carb goes well untill I hit traffic and engine temp goes over 90 then missfires and appears to suffer from petrol stavation and breaks down completely untill temp drops below 90 .
Can anyone suggest a cause as this is a real problem.
Have replaced coil, plugs,leads,points, condenser,distributor cap, what alse can I do ??.

I used to have this problem with an MGB, it had been fitted with (I think) 1 3/4" SUs, instead of the 1 1/2" as standard. The "restorer" had then omitted the heat shield as it wouldn't fit. I was advised by a local specialist that it was fuel vapourisation caused by the overheating.
It had a fast road cam and lightened flywheel, and was uprated to 2 litres from the original 1.8l. Great on the open road but a complete pain in the whatsit round town! Thirsty as hell too! 20 mpg round town.

It's not got a waxstat HS4 has it? If so, first port of call is to spend 2 pence binning the wax pellet.

How hot is the temp gauge reading when it starts to play up? And can you be sure the gauge is reasonably accurate?

I can't see that underbonnet temps should be high enough to cause heat related problems at the moment, but it's possible I suppose. I'd start with a quick check for a spark when it cuts out, and then move to the fuel system. Though I really would bin the wax bit first if it's got one.

Packedup wrote:It's not got a waxstat HS4 has it? If so, first port of call is to spend 2 pence binning the wax pellet.

How hot is the temp gauge reading when it starts to play up? And can you be sure the gauge is reasonably accurate?

I can't see that underbonnet temps should be high enough to cause heat related problems at the moment, but it's possible I suppose. I'd start with a quick check for a spark when it cuts out, and then move to the fuel system. Though I really would bin the wax bit first if it's got one.

I don't know if it's got a waxstat or not where would it be and how do you remove it??

I did have a link to a write up for how to mod the jet to remove the wax stat thing. Unfortunately it doesn't go any where now. I may have printed it. Basically you take it apart and replace the wax stat with two 1p pieces.

Have a look at

http://www.rimmerbros.co.uk/spitfire/images/42a.gif

to identify the jet we are talking about.

Does sound like fuel supply problems. Start by fitting a lower setting thermostat in the engine. Also - if you have it connected - disconnect any water heating supply to the inlet manifold, far better cold! when this happens - is the fuel pump clicking away like a demented chicken ?

yes the fuel pump does go ape when it happens.I am beginning to think that the radiator and fan arn't up to the job it's one of the old type before air intake to the heater and was for a 948cc engine have tried a lower temp thermostate with no luck

Radiator should be fine for the job - it's whole lot bigger than a Mini rad! You could try a 4 blade fan (actually two x 2 blade fans bolted together) - or even a Spridget 6 blade fan. But it is the dreaded 'vapourisation' of petrol in the rising pipe to the high mounted fuel pump. I used to think this never happened - but have had to change my opinion after several peeps on here have reported the problem. One answer is to abandon the electric pump - and use a mechanical pump (as on the Mini) driven by the camshaft lobe. Obviously only possible if your block has a little blanking plate where the pump would go on a Mini. Does it ?

The spridget block i have in the garage does...

The spridget block i have in the garage does...

Thanks for all your suggestions but I think I've solved the problem the garage that fitted the engine changed the metal fan for a plastic one and put it on so that the air is being blown from inside the engine compartment out through the radiator also Ithink muli-bladed fans require a shroud to work properly so it's back to the original metal fan

Ahh they fitted a mini fan then.... :s