red hot exhaust manifold - lt40 2.4 petrol/lpg

Your getting closer like you say but it needs to be right after all the work you have done.

I'd consider contacting HH as suggested and maybe send them the old dizzy.

They might be able to modify the dizzy to take account of the higher compression and modified pistons.

My gut feeling is that it is the mods that have increased the vacuum, so even a new dizzy is still going to be wrong.

Then we swapped the vacuum ports for the advance and the choke.....an all of a sudden its doing normal stuff again. As if it was plugged into the incorrect port, which it most definitely wasn't.

My main concern though, as I took it out at night, is that the manifold still glows cherry red when you are sustained above 3000rpm. 

This can't be retarded ignition, because i can see exactly how advanced It is. So only other things is that its running too lean at high speed or has blocked exhaust.

I'm starting to think that the modification that was made to my carburettor is the problem. This glowing manifold only tends to happen when you are driving on the top end of the engines capability with throttle fully open as if it gets leaner the faster you go. 

The mod we made to the carb was to make the second venturi valve open mechanically instead of with the 2nd stage throttle vacuum which was knackered on mine. So when you put your foot down, both butterfly valves open at the same time, instead of sequentially as it would have been with the vacuum activated throttle. As I understand it, that second butterfly valve in venturi number 2 should only ever open with its vacuum right at the top and of the throttle range. Meaning that potentially im sucking too much air in too early.

Of course the chap that helped me to modify the carb would say this isn't the problem, but I'm starting to think otherwise.

Also, if i think back far enough I think the two events coincided. The modification and soon after, my noticing the cherry red exhaust.

Disconnect the linkage on the carb and increase the gas via the adjustment valve.

See if it still runs hot. As you say no jets etc being used but you are still pulling air in via both chokes.

Results as follows:

Idling at 1150rpm

CO was high first time around at 4.53 when it should have been less than 4.50

Second test after two quarter turn adjustments of the CO screw brought it down to 2.33

HC was fine on both tests and came out at 234 out of a possible 1200

He also seemed to think that a red exhaust was not too worrying but I've bought a bunch of titanium fibre exhaust wrap and some tin shroud to protect the wooden coach-built underbelly from potential fires.