Morris Minor Owners Club

I have a 1275 midget engine running on a standard setup but with a 1.5" stainless LCB exhaust manifold and a single HS4 on an aluminium water-cooled mini inlet manifold. Having been off the road for 13 years sitting in our garage I have just got it running for my sons wedding a month ago and it performed faultlessly. However, while it starts and runs well, it does not like fast accelerating or going up hills. The engine stutters and there is a lack of power. It quickly runs out of steam on hills but if you pull the choke out, it cures the problem and pulls well.

It seems to be a fuel starvation/weak mixture problem as if the choke is pulled out when the problem occurs, it accelerates as it should which seems to indicate the engine is not getting enough fuel at peak load. It has a new distributor (thank you Distributor Doctor) and I have set up the timing with a timing light so that should be spot on. It has a new fuel pump which can be heard pumping with demand. The carb had a BQ (rich) needle in it and I swapped it for a DZ (standard), but this made it worse, which would seem logical. I have reset the jet by winding it up into the carb until flush and then taking it out 2 turns. I have now taken it out by about 3.5 turns and the problem is still there. The float bowl was checked and cleaned and it has a viton-tipped float needle. I replaced the old dashpot spring with a new 'red' one. The plugs look normal and light brown.

How much further should I wind the jet down? Would a different needle make a difference and if so which one? Should I replace the HS4 with an HIF44, which I know a lot of people have good results with in the larger engines?

My first thought - check the float level in the carb bowl. Sounds like your engine runs fine except when under heavy load (like going up a hill).
Tom M.

Thanks, yes that was set up when the float bowl was cleaned. If that was the issue, I don't think opening the choke would make much difference.

Does the carb have a identity tab i.e. AUD354.
What needle is currently fitted to the carb?
I would treat the engine as if it was a 1275cc Marina unit as a first off and I would suggest that if not already fitted you start with a AAQ needle.
The spec of a Marina is exactly the same as the 1275cc Midget except for the twin carbs and ignition.

The carb is AUD374 and it has a BQ needle fitted. I will try AAQ. Thanks.

The AUD374 HS4 carb is originally from MG 1300 and was fitted with a DZ needle.
Now I know the origin of the carb I would try a DZ needle instead of the AAQ needle I first suggested.

I tried the DZ and that was worse than the BQ now fitted, which is a richer needle.

Ok.
Personally I would not purchase further needles but modify the existing needle.
To modify - file a small flat on the needle over its middle part. Fit the flat towards the air cleaner.
Try the car and see how you get on.
Years ago before the wide availability of needles and information this was how I got the needle mixture right.
Car and Car Conversions booklet 'Tuning SU Carburettors' is well worth getting hold of. In appendix 2 of the booklet it gives the dimensions of needles which can be compared to determine the size required against fuel supply.
On page 10 of the booklet there is a diagram which shows what part of the need is used for i.e. pick up and cruising which will inform you where to place the flat.
https://www.ebay.co.uk/itm/234647146809 ... R-DN6sfYYA
There are other SU carb books out there but the C&CC booklet gives clear and concise information.

Tuning SU Carburettors - I bought a copy of that many years ago. Hope it's helpful to you.

https://tecb.eu/onewebmedia/Tuning_SU_Carbs.pdf

Tom M.

Nutmeg
Many thanks for posting the link - most useful and now saved to my favourites.
My copy is 1968.
Phil

Try blowing backwards through the fuel line from the pump to the tank, the tank pick up has a gauze on it which can easily get blocked, it'll probably block again (ours did) but it gives you an indication of what is going on.

Also make sure it has oil in the dashpot, I was amazed the effect it had on ours when it ran dry.