Norton Dominator Hot Starting

[gibbons65]

I Have a 1957 Norton Dominator Model88 (500cc) It starts and runs great from cold, but once it warms up it is a mare to start. The magneto produces a big fat blue spark both when the bike is hot or cold so the problem seems to be carb related It has a Amal Monoblock fitted which I belive is the original fit.

[Justin_Faithfull]

Sounds as though you have magneto trouble. A common symptom of magneto trouble is that they start & run fine when cold, but break down when hot. Checking the spark when the plug is earthed against the head is not always a conclusive test as the plug may spark well here, but may not neccessarily spark when under compression in the cylinder.
Your bike is correct in having an Amal Monoblock carburettor fitted.

[Bruce]

Hot starting problems are usually caused by the Mags condenser failing I had this problem on mine,try getting the plugs out putting some pencil grafite on the plug contacts without bridging them this will give a bright spark when you kick the engine over.I had to do this for quite some time until I had my mag reconditioned

[Rex]

To add to the above, you can do a permanently-temporary fix by connecting a capacitor from the central LT mag connection (the connection going to the kill switch) and earth.
This will prove the internal cap is duff or not, and if it is, will allow you to keep running the bike until such times as you can get the mag rebuilt.