Overheating issue

[Keith in Norfolk]

Could somebody tell me if my SU carbs were slightly out of tune would this cause the engine to overheat and cause backfire ? the problem i am having is after about 15mins driving the temp gauge starts to climb and the engine overheats . i have replaced the thermostat and otter switch which for some reason did not turn on fans when it should ? for a temporary solution the twin fans are now wired to come on soon as the engine starts , however despite this the engine still overheats ,
Main symptoms are :-
1 Engine starts after many turns with pops and backfire.
2 hard acceleration also causes backfire.
3 engine overheats and fills header tank. HELP

[bitsobrits]

Sounds more like an ignition issue, but could be carbs. Carbs would have to be way out to get the symptoms you describe. Is it popping back through the carbs or through the exhaust? Did the symptoms start suddenly or grow over time?

[DWW]

I think there is a subtle difference between overheating and boiling over. Did you check the water pump/belt or the thermostat. What are the spark plugs telling you? Valid question is whether it happened gradually over time or a sudden fault, did the car ever run normally? Is the ignition system working as it should or the timing has changed? is the choke stuck on?

[cactusman]

If it behaves ok for 15 mins and then starts to climb suddenly it seems less likely to be ignition. Unless the carbs are hugely out of tune I doubt they are the issue...I wonder slightly about head gasket...might be worth doing a carbon monoxide test at the header tank...mate had a similar issue on a mini marcos...turned out to be a failed head gasket...

[Series1 Stu]

What about an overheating ignition coil? 15 minutes is about right for a failing coil to make itself known.

Regards

[cactusman]

Or a failing rotor arm....after market ones with a rivet are notorious...