Practically Classics Forum

I really can't see why you are getting this mega high idle and I agree an induction leak will not cause revs to rise, more likely to stagger or die - most engines of the period take a vac feed to the dizzy and a large feed to the brake servo if you have one, is this capped off or connected? A servo leak problem would have an effect on braking and engine running though I doubt wether this would cause high idle . Easily sorted though disconnect and blank it at the manifold and see what happens.
I have experienced a distribitor vac disconnected and it just made the engine run a bit rough when cold and hicup on accell.
A thought - the imp engine is canted I believe. The SU is side draft, so unless you have a cranked manifold maybe the carbs are not sitting level. With the float chambers and dashpots on the slant this is maybe the root of the problem

It has a vacuum take-off for a servo, but this car has no servo so I blanked it off. The manifold is the correct one for twin SUs on an Imp. The dizzy advance pipe is connected fine. It`s a bit more than mega high, it`s like wide open throttle high! So, after all this, is it safe to say for definite that it must have an induction leak somewhere?

Yes. Probably downstream of the throttles which would have the effect of causing open throttle-like behaviour.
The breather shouldn't vent to atmosphere other than through the type of oil cap that has a gauze filter inside. That stub isn't supposed to be open to the atmosphere though its not being connected wouldn't make things this bad.

Any chance of posting images to show the layout of the throttle linkages, the fast idle cams and their adjusters, the complete manifold, the cam cover - emphasis on that open breather - and the baseplate of the airbox please?
There may be something that's obvious to someone who's looking at it afresh whereas you'll doubtless have become sick of looking at it for now and might have overlooked some daft wee thing.

It still has the gauze-filled flametrap, then it vents to atmosphere. Very few Imp owners keep the rubber pipe connected to the airbox, it just hangs down and points at the deck, doesn`t cause this type of issue, if any, it helps it breathe better and doesn`t cause air filters to bung up 2 or 3 times a year. I can`t post fotos as I`m away from home now. I can tell you that the linkages and everything else mechanical on the carbs is set up spot on. Not sure why you`re interested in the baseplate of the airbox? It has 2 pancake filters on it.

brinylonshirt wrote:It still has the gauze-filled flametrap, then it vents to atmosphere. Very few Imp owners keep the rubber pipe connected to the airbox, it just hangs down and points at the deck, doesn`t cause this type of issue, if any, it helps it breathe better and doesn`t cause air filters to bung up 2 or 3 times a year. I can`t post fotos as I`m away from home now. I can tell you that the linkages and everything else mechanical on the carbs is set up spot on. Not sure why you`re interested in the baseplate of the airbox? It has 2 pancake filters on it.

Just to see where the end of the breather pipe should attach. Breathers of that type don't cause problems on healthy engines so anyone who's forced to run without really should be looking at a cure rather than peeing oil all over the road. I did say this:

JPB wrote:its not being connected wouldn't make things this bad.

However, by removing a source of sub-atmospheric air pressure from the top of the circuit, there's next to nothing to scavenge the fumes from the crankcase side, so how anyone can really believe that running with a breather missing would help the engine to run better is beyond logic.

There has to be something that you're missing and by posting these pictures, someone may well see it staring at them. Confusingly; you're 100% sure about all of this yet you're away and can't see let alone take photos of the engine in the areas that should tell us at least the rest of what we need to know.

Why is it confusing you that i can be away from the car and be 100% sure as to how things are with it? Does everyone have to be available with camera in hand to take photos prior to asking a question here? And if they can't be, the response is as above?
Tell you what, i'll forget that i ever asked the question.
Thanks for the advice everyone.

Too many conflicting pieces of information about what your engine has and what it ought to have were what made me feel that, with these photos, we'd get to the bottom of this.

One good picture can be worth many words, many dozens here probably. Fair enough, run it with no form of crankcase breathing fitted and a pair of pancake filters. I still believe that you'll come back to it refreshed and will spot something obvious that tallies up with the symptom you're chasing.

If you have a photographic memory then I apologise for doubting for a second that your first priority while you're away would be to remember each tiny detail of an engine that's not in your physical possession.

Good luck with it.