305 alternator conversion

[bpmcgee]

My '61 has been converted from a generator to an alternator.

I recently got the correct Stomberg carb on it, and took the time to set the idle mixture and speed. I set it at 500 RPM, which is just slightly higher than recommended.

I notice, however, that my ammeter is in the negative when I'm idling. With no accessories running.

Do people put a smaller pulley on their alternator to improve the output at idle? What size do people generally run?

Brian

[AZKen]

Well let's not go there yet. Describe exactly where needle is on ammeter. Just barely into neg or ?

Several test first.

1. First check voltage across battery posts with a multimeter. Motor not running. Report number.
2. How high does idle need to be to get to plus on meter?
3. One wire or three wire alt?
4. What max amperage rating is alt? 63, 78, 100 amps or ?. What model of alternator. I.E. 10SI or 12SI or ?
5. What size is pulley on alt? Size of crank pulley? or water pump pulley size if that drives alt.
6. Check belt tension. Test voltage output of alternator. Motor running test at 500 RPM and at 1200 RPM. Touch multimeter red lead to red alt stud. Touch black meter lead to neg battery post (not to alt case). Report numbers. Further test may be advised after that. We will see.

It is possible, after I know what RPM it takes to get to plus side of ammeter and what is output of alt, that what you see is OK. You don't stay at idle very long to have any impact on charging battery. By my calculations, ~ 85% of rural/cruising driving is higher RPM's than idle. We will look at your pulley ratio but I don't think you have a pulley problem.