Hi everyone.

Without wishing to seem like I'm just aimlessly swapping parts...

I have two carbs with my car, the one it came with seemed quite worn and noone could get it to run or idle properly, so I've swapped it over with a spare. The spare runs smoothly and idles properly, but didn't seem to have any power over 4000rpm -ish, so top speed was 65 at a push and long hills weren't great.

The original carb seemed fine up at higher revs, so I popped that apart today to have a look at the secondary jets. It had a 90 fuel jet fitted where the spare had a 87.5, so I've swapped them over. Both secondary air jets are marked 2AA, but the one in the carb with no power is much bigger than the one in the old carb, so I've swapped that over as well.

I haven't had chance to have a go and see if this has made any difference yet, but I'm hoping it'll give me the nice idle of the "new" spare carb with the higher performance of the older one. The fact the two 2AA air jets were so different seemed strange, so I was wondering if it had anything to do with the numbers stamped above the 26 and 18 on the bowls.

The carb that came with the car with the 90 fuel and smaller 2AA jets is marked 15 A5 92 04. The spare I've been using with the 87.5 and much larger 2AA is marked N2 92 03 (if I've remembered right).

Thanks.

Have you checked the primary jet as these do the bulk of the work?

Also remember the golden rule when fettling/fine tuning the carburation; change only one thing at a time.
That way, you can gauge the effect of a change that's just been made.

If it's of any help, the effect of that air corrector jet with the smaller bore will be to produce a richer mixture at higher volumes of air flow through the carburettor.

By changing to a larger fuel jet at the same time, you've enriched the mixture through the secondary barrel by two separate changes.
The larger bore of the jet will have an effect from first opening of the secondary butterfly, then the air corrector jet affects the mixture at high flow rates...

...and are both carbs the same sized chokes?

Thanks guys. Primary is a 107 and the air jets for that are both stamped 1F2 and look identical. Both carbs are 18/26. I'll try as Ken suggests and just try the fuel and air correction jets on their own tomorrow first and see how it goes. I'll update here how I get on.

Thanks Ken, tried the smaller air jet with no other changes and it seems to have worked perfectly.