1000cc Ford Pre XFlow problem

[ChevronB19]

Hi folks,

I realise the answer to this is ‘take it to a rolling road’, but before we do that (there isn’t one nearby with expertise in SU carbs) I thought I’d see if anyone here had any ideas.

In summary, 1000cc semi race pre-xflow engine. Iron 3 bearing crank, but with race cam, rods etc. It has 1.5 inch SU’s (probably a bit too big to be honest, but 1275cc race A35’s use 1.75 inch).

When stationary, there is a flutter at around 2.7k rpm, but it will rev through that after some hesitation. Under load, however, no way will it go above that, and also takes an age to get there.

Any ideas? Have tried changing needles from what we have available, but no joy.

Any tips much appreciated.

[23.7]

A couple of questions

Any recent changes to the car, Is this a recent problem or is the car new to you?
Is the HT side of things in good order?
Have you checked the fuel flow/filters/pump capacity?

[DVandrews]

Do you have fast rise dampers in the dash pots? (AUC 8824 or 8103 from memory) , it’s worth trying some heavier oil in the dash pots to damp the rise of the piston a little more as this should richen the mixture a little more across a transient throttle.

Dave

[LimSlip]

From my experiences with minis, larger SUs on a tuned engine can require significantly richer needles, and enormous lean flat spots that you can't drive through were par for the course until a suitable needle had been fitted (or an existing one modified).

Wideband oxygen sensor kits are quite reasonably priced these days, fitting one would give you a good handle on what's happening fuel-wise, I know I would have given internal organs for such a s thing when I was in my late teens.

[GreenV8S]

You don't mention EGO readings, spark strength or timing. You need to know those things to understand what's going wrong.

[ChevronB19]

GreenV8S said:

You don't mention EGO readings, spark strength or timing. You need to know those things to understand what's going wrong.

Yep, I know that, I’m asking on behalf of someone else. Current theory is valve clearance is wrong.

Oops - edit - sorry that comes across as a bit grumpy, my apologies

Edited by ChevronB19 on Tuesday 12th October 22:21