OK!  With that cam and carb, what is the recommended minimum idle speed? Might yours be set too low to keep the engine running?

I have a 1275 with a bigger valve head with a 544 kentcam and a weber dcoe 40 last rolling road was 87bhp. I'm running standard lights. 

Tell us about your car and engine. Also what lights you are using.
What is your usual idle speed set at? If it is low for the condition and state of tune of your engine, it may be enough to keep the engine turning smoothly but not be strong enough do much more.


All electrical loads do put a load on the engine. Most are not noticeable. Heavy loads like strong lights or heater fan motors or rear window electric heater grids will cause rpm to drop. Putting a bigger alternator on wouldn't change that. So it depends on the size and condition of your car's engine. A stock 850 only puts out HP in the 30's, so those loads would affect it more. A fire-breathing 1275 with 120 hp probably wouldn't flinch.
Consider this: one HP = 746 watts. How many watts are you drawing, and is this while the alternator is trying to restore the battery charge? What amount is your car stereo and amp (if any) drawing?

hi I'm having issues with my mini every time I turn on the lights, heather or any electrics the rpm drop by around 400 unless I put the isle speed at over 1100rpm. iv have changed the alternator to a later and more powerful model and iv had someone check the wiring and the battery it all seems fine I was wondering if anyone could help.