Carburetor problems ?

[beanpole]

My 1098 is fitted with a ‘mini sport’ manifold and what I am guessing is a 1 ¼” SU HIF38 carb as fitted to the 1275 Mini.

All has been fine, in fact probably has been running a little rich as hardly any choke was ever need, even from very cold. Now all of a sudden everything seems to be reversed, I cannot maintain tickover without at least half choke, (at which point it is revving it's nuts off!) and cannot start without full choke.

So I am guessing a massive air leak somewhere to cause the weak mixture ?, nothing obvious strikes me when looking over the carb, any idea’s ?

[Cam]

Well....... the HIF38 is a 1 1/2" carb and was fitted to the Metro. The HS4 was fitted to the Mini. And I think it was a HS6 that was fitted to the 1275 GT, but it might have been a HS4....... anyway, the problem!

The reason that it is revving is that the fast idle setting is incorrectly set. Have a check by screwing out the adjusting screw that rests on the choke cam.

If the engine has just started doing this on it's own then it does suggest an air leak. Has the breather pipe come disconnected or has it split? Is the carb/manifold done up tight and are the gaskets in good order?

There is another possibility and that is that the jet has 'jumped' up to the bridge where the piston rests. It happened to my HIF44. Unfortunately the HIF carbs are a bit prone to this due to the way in which the mixture screw moves the jet. Take the daspot/piston asembly off and have a look at the jet. It should sit a few mm below the level of the bridge, if it's flush then it has 'jumped' and you need to adjust the mixture screw to move it down again.