948 running on HS1 -1953 series 11

[mrmorrisminor]

Hi there, not sure if anyone can shed any light on this question. I have a series 11 and the previous owners have replaced the 803 with a 948. It appears to be running on the HS1 carb from the 803 engine and retains the original air filter. I am having a few issues with adjusting to archive the best running. Currently the plugs are quite black but she does misfire when hot after a long run in traffic, which I put down to vaporisation, which weakening the mixture will only exacerbate??

So my question is, should I be changing be needle? Can 948s run successfully on this set up? Am I fiddling needlessly? Although I've clocked up over 100k minor miles, I've only experienced the world of 1098..... Early Series 11 land is a little different!!

Any assistance would be greatly received.[frame][/frame]
This is the offending vehicle

[bmcecosse]

The H1 carb will be seriously limiting the power from the engine. I urge you to upgrade to an H2 - or better a later HS2. Black plugs could be due to oil burning - or as you suggest - rich mixture. First check - is the 'choke' going off completely? Next - if you switch on the Ign - does the pump tick steadily - indicating fuel overflowing at the jet - due to worn/leaking needle valve in the float chamber. The jet in the old H1 may be well worn - and similarly, the needle. I have no idea what needle to recommend for an H1 on a 948.....an HS2 is a much better bet. Misfirng when hot could well be failing condenser or tight points gap - or even just 'old' spark plugs. Are the valve gaps set correctly? They can close up when hot, causing misfiring. I suggest 15 thou gap on the exhaust valves (as did MG Rover) to help prevent this. Try a few tests and then come back to us with the findings.

[mrmorrisminor]

Hi, thank you. I have had a good check over this evening. After checking it all over I took her out to warm her up and cut back the mixture bit at a time, checking the plugs as I went. I've now got it to a point where there is plenty of performance (I mean in series 11 terms) and the plugs are a golden biscuit brown. Yet to see if it performs in traffic after a long run however.

It was a bit dark but managed to get a photo of the carb:[frame][/frame]

Am I right in thinking this is the H1?

[bmcecosse]

Well done ! And yes - that's the H1. If it's any consolation - they fetch good money on ebay!

[mrmorrisminor]

Haha! Well if I can I'd like to stick with it, for originality sake, not too fussed with my other minors but I'd like to keep this old girl as true to form as possible. I'll run her for a few days and see how she fairs. It goes surprisingly well, pulls quite nicely

[bmcecosse]

It will do - with the 803 final drive ratio !

[mrmorrisminor]

Yes! It does have slightly short legs!