Hi All, I started my 425 nailhead for the 1st time today since putting it into a custom build. It sounded awesome and I'm excited but I need some pointers. The idle seemed high and after driving the car in a circle for about 2 minutes the idle kept getting faster and faster to the point I had to shut it down, it was really racing. After shutting it off a cylinder or two fired again and then each side backfired once. I built the car but I'm no expert in engine tech. I'm guessing the carb needs rebuilt as it is leaking fuel which is why the RPMs kept increasing and why it backfired? Does my thought process make sense? The carb is a Carter AFB. Pics attached because...well, why not! Thanks for any help you all can give me.
Thanks, I didn't think about the timing, would that make it keep increasing RPMs? I'll re-time it and make sure the distributor is tight.
The 401/425 has an exhaust heat passage in the manifold just under the carb. You have to use a steel plate in combo with the carb gasket to block that passage off..... otherwise you will have a huge vacuum leak at the carb base. The 'U' shaped cutout in the pic is the heat channel. https://www.ebay.com/itm/3324127166...VzEwdxAxAzvJpE1vp_n1pEN6cSvJRttUaAuLvEALw_wcB
If the timing is advancing, the rpm's will increase. If you can verify extra timing, check the advance weights under the rotor to be sure they return to their rest position and aren't sticking 'advanced'. Also check the vacuum advance unit.
I found a small vacuum port that was open and my vacuum advance on the distributor was bad so we'll see if fixing those two things solves my problem. The engine got hot fast and I read the vacuum advance helps keep it running cool even at idle. I also ordered a new water pump as I'm not sure coolant was circulating well and my electric fan wasn't kicking on (I forgot to ground the inline radiator hose thermostat switch). I feel like I'll be chasing issues on this car for awhile!
