Morris Minor Owners Club

Joemog was feeling a bit off-song on the way home the other night so with a bit of time at my disposal this weekend I decided to take the plunge and fit the water heated manifold in place of the one piece cast jobbie on his 1275 Ital lump. this is mated to the unchanged HS4 carb and standard 1098 air filter casing.
Now he runs even worse. Maximum choke is only just enough to hold idle, acceleration is hesitant and 'tight' and the throttle resonse is not linear. Now that sounds to me like it's running lean, however all the plugs are black and dry. Compression is 130 to 140 across all cylinders. The points are worn but clean. So far we have fiddled with the mixture and the points gap with no luck.
Any ideas?

The compressions are very low - 160 psi is more reasonable - however if all are the same it may just be the gauge. Check and set the valve clearances - 12 thou inlets and 15 thou exhausts to guard against valve seat recession. There is absolutely no reason to have choke at idle - so get it set to the correct mixture without choke. Check with the 'lift' pin. And check the piston rises easily with a finger - and falls with a clunk. Put a little engine oil in the damper. Try running the car without the air cleaner fitted - it's far too restrictive for a 1275 - mine even 'chokes' my 1098 - i have to run without at the moment. And has the hole where it fits to the carb been opened up to match the new 1.5" SU - and is it blocking off any of the little holes on the front face of the SU ? Also worth advancing the ignition timing a bit until it 'pinks' when labouring in top gear - then retard until it doesn't, quite. Also check the vacuum advance unit is working - and is it connected to your new manifold ?

BMC, everything is as it was. Only the manifold has been changed.

Aye - but you say it wasn't well before either. What's the manifold from - and are there any unused stud holes allowing air to enter ? And is the carb sitting with the float bowl vertical?

It was running slightly off song - which I put down to supermarket fuel, which I have avoided before.
All holes are plugged. The manifold does tilt the carb a bit more than the previous one.

Oh hang on that float chamber angle is a bit steep...

Shouldn't there be a spacer in between?

Theoretically, yes - an "insulator"

is it important?

AFAIK it's a heat insulator (block>manifold>carb) so it can only be good, I'd have thought. Doesn't restict air flow...

The spacer also lengthens the inlet tract, which for reasons I never quite understood and now can't remember can be considered a good thing.

Though I doubt it's the reason for the poor running in this case

The spacer is not too important - but that float bowl angle is no use! You must get it vertical. At present it will be flooding fuel down the manifold. If you study the attachment for the bowl - screw from the other side - there is then an angled spacer that sets the bowl angle. Either file it or maybe turn it over - or even throw it away - and then set the bowl vertical - and re-tighten the screw!. No doubt Burlen will sell you a different angled spacer - but you can just modify the one you have.
I say again though - that air cleaner is far too restrictive for a 1275 engine. Even the empty casing holds my modified 1098 engine back at high revs.

but that float bowl angle is no use! You must get it vertical

Thanks BMC Glad it's something obvious. The daft thing is that I knew the manifold was at a steeper angle. I couldn't shut the bonnet with the previously used trumpet because the airbox was high.

OK job done. Now Joemog runs but I can't get the mixture right. it's not far off. I have lifted the pin and the revs rise even though the jet adjustment nut is right up. This sounds like a worn or inappropriate needle but I'm open to other suggestions - after all I haven't got it right first time so far!

Oh one other thought! In levelling the float chamber, the flexible pipe from it is really tight and may well be pulling at the needle assembly.