Spitting back through carbs

Hi,
Can anyone suggest the most likely cause of "spitting back" through the webbers on my two litre nord engine. I have checked for air leaks but am beginning to suspect burned/leaking valves. Grateful for any ideas.
cheers

Spitting back normally means the mixture is too weak and/or the timing is retarded so it might be worth having a play with that to start with. Bit of light reading here...
Selection and tuning of Weber DCOE Carburettors

Are you using decent octane petrol? These engines were originally setup for five star fuel. They don't need lead, but they like octane!

Many, Many thanks for that. It looks really useful. I did a compression test this afternoon and all pressures were quite good and ranged from 175 to 190 psi so I guess the valves are ok. Think you might well be right about the timing so I'll have a go at that tomorrow - but I cant see how it can have "slipped" unless the distributor clamp was lose?
cheers

The ignition timing will change as the rubbing block on the points wears. One degree of dwell change equals one degree of ignition timing change (to the retard side).
Check the dwell angle at idle as well; should be 60 degrees. Then rev the engine. If the dwell changes by more than about 3-4 degrees, the dizzy shaft bushings are worn.

Assuming you have points, that is.

Papajam,
You are a prince among men. When I removed the dizzy cap I discovered I had electronic ignition (I've only had the car a few weeks), which is good, but I could not blame the points. However I've got the car running perfectly by giving it a bit more advance -- Great tickover and no spitting back. However, when I put the strobe light on the (hardly discernible) timing marks I find I'm running a few more degrees advance than I should (at 800 rpm with the vacumm plugged). Car now idles and drives great but I'm slightly worried I might now be running too much advance at full revs (though I do run on 98 octane fuel plus Tetraboost lead additive).

If your engine is happy then there should be no problem. The lead additive will give a degree of protecttion but this is strictly not necessary as an additive as the engine will run quite happily on unleaded.

Your specific engine's compression, state of tune, camshafts etc will determine the ideal advance more correctly than the standard marks for the "average" engine would show, whatever that may be...

To add to what Ian said, running a bit more advance than 'standard' isn't generally a problem as long as you're not getting any knock (detonation.) You might find when the weather gets hotter that you have to retard the ignition slightly. Using high(er) octane petrol will reduce this risk.

w