My '66 coupe will be sitting at a light, idling perfectly fine at about 900-1000 rpms
then she'll suddenly bog down and I'll have to throw her in neutral to keep her alive.

The battery is good, carbs fine, and she runs perfect 99% of the time, this only happens while sitting at a light

I have a 289 with a c4

 

Sounds like it could be alot of things. I dont know much about 289s but a 1000 RPM idle while in gear sounds a bit high to me. Your engine bogging is most likely a vacuum leak somewhere...or a foul plug. Try pulling plugs to find a culprit, or checking your vacuum pressure for a leak.

Keep us posted.

 

I replaced the plugs not too long ago, and a few of the really bad hoses, but not all of them.
If it could be a vaccum leak, then I'd guess it is. Some of the hoses were pretty bad, and some were barely doing anything at all.

 

you might have a intermittent vacuum leak, that corrects itself and brings that idle back down where it should be, about 600-700 in drive. Check for a cracked vacuum hose. Since there aint much for vacuum lines on the early 65-66, i'd look at your vacuum line to the vacuum advance, or the vacuum line from the manifold to the tranny vacauum modulator. if everything checks good I'd consider pulling the top of your carb and clean the dirt out of the fuel bowl and spray the needle/seat with a good dose of carb cleaner. you probably have rust and dirt in the float bowl. don't bend the tong on the float because that will change the float bowl setting. you should be able to lift the float and needle together, straight up, as one, then set it back in once it's all clean.

 

when you have power assisted breaks check on that vacuum hose as well.
maybe the issue has to do when you're sitting on the breakpedal (traffic light ....)

Kalli